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Oral History Transcript — Dr. Keith Boyer

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Interview with Dr. Keith Boyer
By Robert W. Seidel
At University of Illinois, Chicago Circle
November 5, 1984

 
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Keith Boyer; November 5, 1984

ABSTRACT: Boyer, former head of the laser division at the Los Alamos National Laboratory, discusses the origins of the Los Alamos Laser Program, the influence of Air Force Weapons Laboratory (AFWL) High-energy Laser Program on his own program, the connection with his earlier nuclear rocket propulsion studies; Abraham Hertzberg’s proposal of the gas-dynamic laser concept and his visit to Los Alamos to discuss laser function. Los Alamos’s growing interest in laser fusion in the 1960s, their awareness of Ray Kidder’s work at Livermore, the three-pronged approach to laser fusion taken at Los Alamos, the development of interest in chemical lasers with AFWL support; in glass lasers; carbon dioxide laser fusion work; development of the electron-beam CO2 laser and patent dispute with AVCO; the Division of Military Application interest in isotope separation and weapons simulation; comparison with the Livermore program; molecular isotope separation program at Los Alamos vs. Livermore and Exxon Nuclear exploration of the atomic vapor process; influence of Basov & Aleksandr Prokhorov’s work and others on Boyer’s group; technical problems of compressing thermonuclear fuel; electron attachment instability; problem of the wavelength effect; computer codes and modeling; laser fusion target design; laser system designs; frequency conversion work for isotope separation; large CO2 lasers at Los Alamos; self-oscillation and target reflection problems in them; resonator optics of large CO2 laser; Helios Design; Antares design; Boyer’s High Energy Laser Review Group participation and the contrast between Dept. of Defense and Dept. of Energy research and development policy.

Transcript

Seidel:

We are with Dr. Keith Boyer at the University of Illinois Chicago Circle discussing his experiences in the laser research and development there. He has begun to talk about the origins of the Los Alamos Laser Program. If you would start again, I'd appreciate it.

Boyer:

In the late sixties, in 1968, as I remember, we first became interested in laser activities, after learning about some classified programs being conducted at the Air Force Weapons Laboratory at the Kirkland Air Force Base in Albuquerque. After obtaining the necessary clearance and authorizations, we obtained information on this program, and had several ideas of how we might contribute, not only to help the program of the Air Force, but also to develop new technology relevant to the work of the Atomic Energy Commission, in which we were engaged at that time. The program that I was involved in then was the nuclear rocket propulsion program, known as the Rover Program, in which I was in charge of all the field test operations for that project. We soon realized that, based on the work conducted by the Air Force, that some very high-powered gaseous media lasers were not only possible but were under active development. We saw a possible connection with our nuclear reactor work in which we might use such a reactor to power one off these early laser systems, and actually pursued at some length the possibility of generating a pump for what was called a gas-dynamic laser. It was proposed to take a mixture of CO2 and N2 heat it to a high temperature, expanding it to create a population inversion and then to extract laser energy at long wavelengths in the infra-red.

Seidel:

May I ask one question here? You say you became aware of this work through contacts I presume with Avizonis and his people down at AFWL?

Boyer:

That's correct.

Seidel:

Now, at this time had David Mann put the Eighth card restrictions on this material, do you recall?

Boyer:

There were restrictions on such material in the Eighth card program.

Seidel:

The reason I asked the question about this is, to my knowledge the first public announcement of the gas-dynamic laser, outside of AVCO-Everett research laboratories, was the 3rd DoD High Energy Conference, in 1967. Very soon after that, the 8th card restrictions were imposed, and you say you had to go through considerable problems to get into this, which I presume is partly because of the Eighth card.

Boyer:

Yes.

Seidel:

I'm also in your comment that it is the awareness of the gas-dynamic laser, the Gerry and other work which gets you going on this, the rocket propulsion idea. And I'm interested because of the level off the restrictions, how complicated this was, because one of the problems in high energy laser work has always been, particularly under Eighth card, gaining access, and the restrictions on information. Many people have suggested to me that this was a real problem in terms of doing research.

Boyer:

Oh yes. There was no real problem there.

Seidel:

OK. The other thing that strikes me in talking about Rover which, of course, I'm aware off in some other contexts, the people who are particularly receptive to the gas-dynamic laser's technology, it seems to me, were people who had been in some way or other in the rocket business, because basically what a gas-dynamic laser is, is a big rocket engine.

Boyer:

Right.

Seidel:

With rocket-like nozzles and very interesting technology which is coming, not from electro-optics or quantum optics, but out of this whole rocket technology of the fifties and sixties, and it's intriguing to me that you, coming out of the rocket business in a way, not like chemical rockets but you have to deal with similar problems, pick up on this technology as something that is promising for propulsion. What occurred to me is what this looks like when you look at the paper on propulsion that you did is taking General Atomic's Orion concept of the early sixties, which Freeman Dyson talks about in his book, and combine this with the gas-dynamic laser idea. Those seem to be the two basic concepts that are coming together, is this correct?

Boyer:

That is correct, in one sense, although it's not that simple. The gas-dynamic laser concept was really, to my knowledge, first proposed by Abraham Hertzberg who looked at the possibility of using helium and some other material, heated to a much higher temperature, and creating a population inversion, and by expansion and cooling of the stream containing helium and another gas. But that was something that Hertzberg did not pursue at that time, but it was Arthur Kantrowitz who recognized that CO2 was the obvious ideal medium to use with the gas-dynamic principal to produce a high intensity laser. I think that Kantrowitz was aware of Hertzberg's original proposal, but he saw a way of implementing it successfully which Hertzberg had not done.

Seidel:

I just wonder, from your perspective, in the late sixties, were you aware of Hertzberg's work?

Boyer:

I first became aware of Hertzberg's work when Hertzberg discussed it at a meeting of the Fluid Mechanics Panel of NASA, of which we were both members, shortly after the invention of the laser was announced, Hertzberg was very intrigued by the laser and had immediately proposed the gas-dynamic principle of combining a thermal energy source, followed by an expansion to produce a population inversion, and so, I don't know to what extent Kantrowitz may have been thinking along those same lines. I know that at least Hertzberg arrived at this independently and discussed it fairly openly with many people, and I understood him to say, including Kantrowitz, but I don't think we went into any particular discussion as to whether the basic ideas of the CO2 laser arose from those discussions or not. I'll just ask you since Hertzberg's name has come up. When I spoke to him, he talked of visits he made to Los Alamos around 1965, which is about the time he came up with this idea.

Boyer:

Yes. I was going to talk a little more about his visits, because he did spend a couple of days at Los Alamos discussing an idea he had for using laser energy to produce a fusion reaction, and I understand you talked with him about this.

Seidel:

Well, he remembers talking about that. Of course I don't know what your response was at Los Alamos?

Boyer:

At that time, we were particularly interested in pursuing that idea, primarily because we looked thoroughly in the sixties at the possibility of using laser energy to induce fusion reactions, and there were actually a few calculations — simple calculations — done which indicated that the power required was very far from what was achievable by lasers at that time, and so we didn't pursue this work, although at Lawrence Livermore Laboratory Ray Kidder did pursue this general idea, and actually spent time working on laser systems for the attempt to do some early experimental work in trying to produce fusion reactions.

Seidel:

May I say just a little bit about that? You probably know Project Seaside that was done in the early sixties. This was the ARPA-ONR project to scale up glass lasers?

Boyer:

— no, I wasn't aware of that.

Seidel:

One of the largest glass laser complexes in the world, as far as power goes, was built down at Air Force Weapons Lab, for effects tests at that time.

Boyer:

Yes, I remember, I knew that very well.

Seidel:

So I was just wondering, since you're at Los Alamos which is 100 miles some miles as you drive and 60(?) miles as the crow flies from there, did you in the early sixties know about the kinds of power levels ARPA was getting with glass lasers? Was this an element in your considerations?

Boyer:

Yes. The answer is, we did have some people that worked with or spent some time at the Weapons Lab talking with their people and actually doing some preliminary work at Los Alamos on lasers. There was a group in the weapons test division, which I was in, that was working at this. Andy Koontz and two people working for him, Phil Mace and Dennis Gill were keeping abreast of the work at the Weapons Lab, and were doing some preliminary work on glass lasers. At that time, I was very heavily engaged in the nuclear rocket propulsion work, and only took I'd say, a modest interest in what was going on there, although I did arrange for Phil Mace to do some preliminary work to see if we could produce population inversions with a theta pinch machine. Previous to my being responsible for the test activities on Rover, I had charge of a group in magnetic containment fusion, and we initiated work on theta pinchers. It was clear that one could put heavier gases in the theta pinch and get a tremendous amount of fluorescent radiation out of the discharge, and then we speculated that it might be possible to get laser action, and if we could we might indeed get to very high energy in a short enough pulse to get interesting power levels. But that work was only done on sort of a low level and for a month or so, and wasn't successful at that time. I think Phil Mace went back to school for some period, and so that work was dropped.

Seidel:

I'm interested that you bring up his name because I have read correspondence between him and Ted Saito who was one of the people working on glass lasers at the Weapons Lab, it's in the late sixties. I'm interested to find that that connection goes back I guess to the 1962, 1963 time frame more or less.

Boyer:

I'm not sure just how early. Certainly I think through the 1965, maybe earlier, I'm not sure. Looking at this problem at Los Alamos, as I said, indicated that it would require very high peak powers to do anything interesting in fusion physics, and at that time, we didn't particularly feel that military-related laser systems were in the direct line of the laboratory's responsibility at Los Alamos. And it was only when we recognized the possibility that the Rover reactor might serve as a power source for a gas-dynamic laser that we thought there was a legitimate area for us to investigate. We did discuss this with Avizonis and others at the Weapons Lab, and they were interested in the possibility, but I think it was left on the basis that if we pursued it and we found there were deeper possibilities, then they would be interested and would try and work out some kind of a joint program, but until we had done some work, why, there was not a great deal of interest in pursuing that at the Weapons Laboratory.

Seidel:

You couldn't buy in, in other words?

Boyer:

Well, we weren't that interested in really pursuing it very vigorously. The reason was the following. We actually set up, as part of our test activities in Nevada, a small project in which we investigated the ways of simulating the output of the reactor and producing a pulsed flow that would be suitable or a gas-dynamic laser, using a very fast-acting valve that we developed for the purpose, and did some experiments, where again we used some electrical heating techniques to simulate the reactor output, and set up to see whether this could produce very energetic laser pulses. This work was done actually at the Nevada test site, the Rover site. In looking at the possibilities here, since I had been working on the magnetic containment fusion for some years, I was particularly interested in the possibility of using laser energy to initiate the fusion process, an in the late 1968, early 1969 time frame, we did some back of the envelope calculations that convinced us that we needed quite high power levels, and considerable laser energy. In this work I was able to enlist the interest of Raymond Pollack, who was a weapon designer, and he came up with a number of estimates which indicated that we would not only have to get quite large energy for the experiments, and by quite large, we estimated that we were going to need energies on the order of between 100 kilojoules and a megajoule, and pulse length on the order of a nanosecond or less, and when we did that and looked at the gas-dynamic laser, while we believed we could set up a system that would give us quite high pulse energies out, they would be fairly long pulses because the gas-dynamic laser works at reasonably low pressures.

In looking at the kinetics of the CO2 laser, it was clear that one would probably have to work with a fairly high pressure medium in order to get enough bandwidth to generate the length pulses we desired, and it appeared that the gas dynamic laser was not going to lend itself well to that technique. At this same time, there was the publication by the Bell Telephone Laboratories on their measurements of quite short pulses. They were able to generate pulses in the picosecond domain and, which, they were able to show resulted from a mode locking technique in the laser, and this opened the possibility then of generating very very short pulses and getting very high peak powers. We felt this advance in the general laser technology now made it interesting to pursue the fusion work more vigorously than we had in the past. We were aware of the large glass laser work at the Weapons Lab, and also we were aware that at Livermore Ray Kidder and others were building a large glass disk laser system, and it appeared that that kind of a laser indeed could, if it worked successfully, could produce the kind of energy and powers that were of interest. So I proposed in a group leaders meeting in the test weapons division work be undertaken to try and develop some laser systems that would be of interest in this area, and I described the general ideas that would be involved, and there was considerable interest within the division, in pursuing this.

The division leader at that time, William Ogle said he would be willing to support laser activity in the division, and we agreed at that time that we would divert some of the activity that was at that time winding down in the Rover test program to work on these lasers. We set up as a consequence a three-pronged approach to the laser question. We felt that the glass laser was much closer than any other laser to producing really high peak powers. We thought that the greatest problem facing such a program was getting enough data on the physics of the interaction of the laser energy with matter, with the high temperature plasmas one would be producing, and that in order to explore this physics, we would need some high powered lasers to start with. We were aware that there was considerable interest in the Weapons Laboratory at Kirkland in chemical laser technology as well as the CO2 lasers and the glass laser that they were using for effects testing. So we set up three separate groups, three separate activities. One was to pursue the chemical lasers. The second was to pursue a glass laser system, and the third was to pursue the CO2 lasers.

Seidel:

I guess about this time Ted Jacobs at Aerospace and Cool at Cornell and Airey at AVCO had developed the successful chemical lasers?

Boyer:

Well, let's see, there had been some successful chemical lasers. We were aware of the work of Pimentel.

Seidel:

I was thinking of the HF; the HF had not yet lased successfully?

Boyer:

I think we were, if I remember rightly, we were aware that the HF laser had been made to lase, and so it was one of the ones we were looking at. We looked at a whole series of different lasers, and it was apparent that the HF laser might be the most promising one because of the very high reaction energy involved and the fact that the chemical reaction was known to lead to a population of series of the vibrational levels in H that were all potential lasing levels, although the HF lasers operated at that time operational only from a first vibrational level, and was using the excitation of the others to cascade down and populate that lower level. Well, we were able to hire a professor at Brigham Young University, Reed Jensen, who had previously worked at Los Alamos to come and join our activity and to work on the chemical lasers, and have Andy Koontz's group, primarily Dennis Gill and Phil Mace, start setting up a glass laser that would work in the picoseconds time domain, and I started looking at what one might do is to produce a useful CO2 laser as a third possibility. Now, it was my belief that ultimately a gas laser might be required in this process were to be more than a laboratory tool. If it were possible to release fusion energy in a way that could be adapted to power generation, it would probably require some type of a gas laser, just because of the heat removal problem and the very large volume that we saw that the lasing medium would have to encompass. We did some preliminary estimates, I guess in early 1969, which indicated to us that we would have to have several cubic meters of lasing volume at pressures of several atmospheres to use the CO2 laser, and at that time, except for the gas-dynamic laser, the only electrically-driven lasers that we were aware of were longitudinal discharge running at low pressure.

Seidel:

Things like the "sewer pipe" laser?

Boyer:

Yes. So our question was, could we electrically pump such a laser and use a very large volume and a high pressure and still get that kind of an electrical discharge that would give an efficient population inversion? We spent a lot of time talking to various people, including Walt Sooy — who was at Hughes at that time — we knew that Hughes was working on the gas-dynamic laser and we also talked with some people that were in the Autonetics division of North American, who were working with the longitudinal discharge lasers, and as a result of those conversations, we made some preliminary estimates of what the pressure broadening term would be. This confirmed our estimate that it would indeed take several atmospheres operating pressures. In fact, our estimate was, that we wanted to operate at about three atmospheres pressure. Higher than that, would lead to a number of problems with the medium, and lower than that, we felt we would end up with both too large a device and too narrow a band width to give us the necessary short pulse. We did anticipate that we might have to go shorter pulses than one nanosecond. In fact we had looked at possibilities of going down to 100 picoseconds or so. We set up a small activity to pursue techniques of initiating such discharges, and in June of 1969, there was a meeting which we hadn't been previously aware of that took place every two years, I think, looking at the interaction of lasers with matter, and in that meeting there were a number of discussions of a problem that we had worried about, and that was, it was clear that the wavelength question was going to be a dominant question in this activity.

It had been considered that one would not couple a long wavelength efficiently into plasma produced by a laser if that plasma approached the kinds of densities that we thought would be necessary, because you have a so-called critical density at which light below a certain wavelength will be reflected, and so it was initially thought by Kidder and others that they might have to stay with wavelengths short enough to couple efficiently and so they thought they might have to stay at wavelengths below a micron, and in order to get coupling. However, there was some work reported by Moshe Luben at the June meeting in which he was able to report on experiments which demonstrated one could get fairly efficient coupling to plasmas which were over-dense plasmas, and it was speculated at that time that this was due to various driven instabilities in the plasma. These could result in the laser energy coupling efficiently into the plasma, instead of being largely reflected, as had been originally assumed. This gave considerable impetus to our following through with the work on the CO2 laser, because we felt after that meeting and discussions with Luben and others that it was not all clear what the wavelength dependence would be, and that one would only probably determine this by experiments, since the theory was very complex.

Seidel:

Where was Luben then?

Boyer:

Luben was at the University of Rochester where these experiments were being conducted.

Seidel:

Was he working with Wolf and people like that?

Boyer:

Luben set up the operation I think initially, and his objective was to produce fusion using laser energy.

Seidel:

That's the origin of that activity there?

Boyer:

Yes. To the best of my knowledge, it was initiated by Luben and he did a lot of the early work on the interaction physics at fairly high intensities. He did have a glass laser system that was capable of generating interesting intensities.

Seidel:

But you had plasma physicists over the years at Los Alamos, did they look into this problem?

Boyer:

Well, the answer there I think is that the plasma physicists had been interested in a much lower density regime, and had not done much exploration in this area, and in fact, this was not a well explored area anywhere, when you got into really high intensity. The rules of the game changed quite a bit.

Seidel:

In this particular work, you are talking about something in between 108 and 1015 watts per centimeter squared is that what you're talking about?

Boyer:

Yes, at that time the intensities were primarily in the 109 to 1013 range, I would say.

Seidel:

Because I remember 1015 being cited as some sort of a critical value later on.

Boyer:

Yes, but this was outside the technical ability then. I mean, there were no sources, I think, at that time that could give that high an intensity. However, that followed not too many years after that. As I say, we actually started din June of that year just prior I think to this meeting, we set up a project in what was called J Division, the nuclear weapons test divisions at Los Alamos, to look seriously at the fusion project, and I was able to also get authorization to spend some funds from the Nuclear Rocket Propulsion Program on this area, because we speculated at that time that if we were successful in producing fusion, that we could use this not only for power generation, but for propulsion, and we outlined some schemes in what was called the Space Nuclear Propulsion Office, that was a joint AEC-NASA office to develop high thrust propulsion systems. Now, there were also some space power projects which were also joint projects, and I think that was run under a different office than the SNPO office. And so we felt we had some legitimate programmatic interest then in putting together a modest effort in this laser activity, related to inertial containment fusion, and we initiated a set of seminars at Los Alamos to study what was known about both the interaction physics, laser physics, and also what the other requirements for fusion would be. And while these seminars were in progress, they met weekly for a period of some months, we organized also a theoretical effort to explore both the interaction physics and the fusion physics of the process. We believed that we would need laser systems that could operate throughout what we considered the useful spectrum where one could produce lasers from 1 micron to 10 microns, and also going into the visible as far as the ultraviolet. By this time some of the nonlinear harmonic processes were fairly well known, so we anticipated converting the 1 micron energy into the green, and near ultraviolet, so that we could pursue a more or less continuous spectrum of laser frequencies, to really try to understand the interaction process. The program was 1, to try and develop appropriate laser systems, and 2, to explore the theoretical requirements and 3, to do experiments, as soon as we had the necessary laser energy, to understand the interaction physics. This program then moved ahead with a number of people, several of whom had been working in the magnetic containment fusion, who worked on the theory, and several weapons designers also. Pollack and several others, became interested in the dynamics of the fusion process in this context, which more nearly resembled nuclear weapons physics than magnetic containment physics. We also set up a small activity to pursue the chemical lasers and worked with the Air Force Weapons Laboratory, who had a very vigorous program on chemical lasers.

Seidel:

This is John Rich's program?

Boyer:

Yes, John Rich and others, Avizonis.

Seidel:

I think Rich is the one that, no, Oglukian is the one who first monitored and sponsored the laser work there and then I guess John Rich came in and really got the new laser program going.

Boyer:

There were quite a few meetings in which each group discussed what they were doing, and various contractors were involved and discussed their work, and we actually undertook to make some measurements in the chemical laser area for the Weapons Lab, small contractual activities to help support the work that we were doing in which they were particularly interested in. We had some facilities that lent themselves well to this activity, including cross-molecular beam equipment, and computer programs that could look at the reaction energy surfaces and study the kinetics of the chemical processes in some detail, I'll get back to that work again.

Seidel:

Just before we get off it and before I change the tape... One interesting thing to me about that work at the Weapons Lab that you're referring to is Ted Jacob's impression that the Air Force Weapons Lab wasn't interested enough in chemical lasers and that was probably according to impressions I've had from talking to people at the Weapons Lab, because their concentration on gas-dynamic laser technology precluded them from putting the big effort into chemical lasers that some people thought they ought to have done. Did you feel that they were turning to you in this regard?

Boyer:

Well, I think the Weapons Lab people felt they had some programmatic responsibility to produce a demonstration of the system as early as they could, it appeared that the gas-dynamic laser could do that earlier than other systems, and I think they looked upon the chemical laser as an interesting possibility for the future, and they indeed were supporting some effort in that area. Also there was work going on at Aerospace Company, where Jacobs did a lot of his work, as well as at AVCO and TRW. I felt at the time that there really was considerable interest in the chemical laser, but it was an area that required more preliminary work and understanding of what the critical parameters were. I think they, in principle, knew how to design and build a large gas-dynamic laser. One did not at that time know how to build and design a large chemical laser system, so most of the chemical laser work was directed towards getting a better understanding of the necessary conditions, relaxation rates for the various processes etc.; the HF laser, relied on mixing two reactants intimately and burning them, and this mixing process was not a well developed or understood process. The relaxation rates for many of the complex reactions going on there were not known well at that time, and so there was a great deal of fundamental work that had to be done, and we were contributing to some of that fundamental development work, as were the people at Aerospace and various contractors.

Seidel:

But your particular contribution derives from this cross molecular beam facility which you have?

Boyer:

Only, in part, that, and theoretical or computer simulations.

Seidel:

I know AVCO had large computers, but I gather that your computers in some ways had capabilities for modeling that theirs did not, is that true?

Boyer:

Well, not only that, we were quite strong at Los Alamos in theoretical chemical kinetics, and in particular in being able to set up a potential surface for the reaction in which as the molecules came together, how the energy was redistributed. Sort of an a priori analysis from first principles as opposed to interpreting experimental measurements. There was quite a strong theoretical capability.

Seidel:

Did this come out of the weapons work essentially?

Boyer:

Only very peripherally. Los Alamos Laboratory always pursued a very broad base of physics, chemistry and metallurgy, dealt in general with materials and processes that were of interest in the weapons field, but went far beyond the requirements of the weapons program, and this was justified on two bases, one, it was felt, and rightly so, I think, that one needed experts that could be called upon to address particular problems that might arise in the weapons fields, that could provide new ideas that might change even the direction of the weapons development, and that one could only maintain those kinds of interests, and to retain the necessary staff and their competence, if they were free to participate in a lot of fundamental independent research. And so there was a great deal of this activity that was not only supported but encouraged by the Atomic Energy Commission.

Seidel:

I'm curious about the computer modeling facility and what had been done here. It seems to me you can do theoretical chemistry almost anywhere, but Los Alamos had unique facilities in their computer base —

Boyer:

— in their big computers —

Seidel:

— that you can actually, with your theoretical approaches, you can model a system, about the potential surface of a molecule or chemical system, in such a way that you could do in very few other places, maybe Livermore and Princeton and some other places would have that capability.

Boyer:

Now, you must remember that, one, we felt that we were interested in pursuing chemical lasers in their own right, and operating in a much more, let's say, complex regime than the Weapons Lab was interested in, so we were pursuing both the experiments and the theory, in a way that, and with a capability I think that complemented rather than duplicated any capability that the Weapons Lab had through itself or its contractors, and so they were as a result quite interested in our work. To pursue this point a little further, we could see the possibility of, one, producing much higher energies with a given laser volume, and a given cost laser, chemically than any other way. The specific energy was very high. And then the question was, could you get that energy out in a short pulse in a usable form for fusion work, and also, a wavelength intermediate between the 10 and the 1 micron laser. It might turn out that this would have particular advantages. At that time we didn't know. And so we looked at several possibilities. One was producing an oscillator pulse generator that could extract the energy from a chemical laser fairly efficiently, and in order to do that, it's clear that one would have to combine the two reaction products and burn them very very rapidly, because there was a fairly short relaxation time, and also the medium had very high gain, so that you lost the energy from spontaneous emissions, so that when you had a very large volume in an HF laser. It radiates into 4 pi. So our idea there was to build a small system that would put out a short pulse of high enough intensity that we could sweep through the volume, and extract that energy in a tight beam as, what I guess today is looked at more as an injection lock oscillator, although we looked upon it the main chemical laser volume as being an amplifier. We recognized, if we were going to get a short pulse out, we might have to, in effect, produce a traveling wave, a chemical combustion wave, in the medium. So we really had to understand the kinetics extremely well in this process, and also how you mix and hold these materials stable until ready to trigger the reaction, and how you make that reaction propagate through the medium at the correct velocity. It was again apparent that we would have to go to moderately high pressures for the mixture which can get into a very nasty problem, in having a substantial volume of hydrogen and fluorine or some fluorine-containing compound setting there ready to detonate. It's some trick to make sure that it doesn't create pre-ignite, also to show that you can extract the energy efficiently in a short pulse.

Seidel:

Were you doing hardware studies?

Boyer:

We did hardware studies. We actually set up a small oscillator system in which we could produce a short pulse and were able to show that we could mix the material, stably. We looked at a number of reactants besides just hydrogen and fluorine, various fluorine containing compounds like Ce4 and Ce3 and other compounds, themselves a little tricky to handle, and found how we could mix these with hydrogen and have atmospheric and above pressures, without them detonating, and were able to show how one could then ignite that with an electron beam, and in effect produce a traveling wave excitation so that we were able to extract energy fairly efficiently in the very short pulse. We had schemes to carry this kind of work on, and we estimated if one wanted to get up into the megajoule regime, that this might be the easiest way to do it.

Seidel:

Now, are we talking about the actual active medium being always hydrogen fluorine, or are you talking about DF as well?

Boyer:

We would prefer hydrogen and fluorine rather than deuterium and fluorine because we wanted the shorter wavelength.

Seidel:

You weren't worried about the atmospheric propagation.

Boyer:

We weren't worried about the atmospheric propagation. As I say, we had an active program up to about the time that I left the program in 1976, on the hydrogen fluorine. Now, we always had some reservations about the chemical laser, of which the hydrogen fluorine was the best, in that you can show on fairly solid grounds that about the best you would expect to do in energy extraction is like 11 percent or so of the energy generated. You then would have to reconstitute your hydrogen and fluorine, if you had any kind of repetitive system of power, propulsion or whatever, and so we felt that it was questionable whether one could come up with a viable system just on the basis of efficiency alone for that. On the other hand, we felt it did offer considerable possibility of doing a lot of both the demonstration work, and also as a laboratory tool, and we set up a substantial facility to pursue this work, and as I say, carried it to the point where we showed you could extract energy efficiently, could generate short pulses, and so on.

Seidel:

So this work, just to put in a time-frame, began about 1969.

Boyer:

Yes, this began in late 1969 or early 1970.

Seidel:

And continues to about 1976?

Boyer:

Continued till 1976.

Seidel:

About that time it was shut down?

Boyer:

Yes, and the reason for that later. There was another possibility, in hydrogen fluorine, that one of the members of our group, Theodore Cotter, came up with, and he did some calculations which showed that one could produce a self-igniting propagating wave in a hydrogen fluorine mixture, at the right pressure, that you could get what he called a photonation a process in which, when the laser pulse, intensity got high enough, it could essentially ignite and drive the reaction itself and extract the energy as it went, so you would initiate the pulse and it would carry itself through the system and extract the energy fairly efficiently.

Seidel:

Sort of like swept-gain Dicke super radiance?

Boyer:

Well, it's not quite —

Seidel:

You have the combustion thrown in at the front end?

Boyer:

— It's rather complicated. You can show, though, that such a wave will propagate, and it's a rather interesting concept that has never really been demonstrated, but I think we all believe that in principle it could be done. Again it's just a question of the stability of the mixture, whether you can go to even higher in pressure.

Seidel:

But the radiation would come out largely by simulated emission?

Boyer:

Oh yes, it would come out in a good quality narrow pulse.

Seidel:

That's because the higher energy levels tend to cascade down and feed the stimulated emission process.

Boyer:

Yes.

Seidel:

So essentially you're turning all the energetics of the fluorine atom into lasing.

Boyer:

Well, it would be a more efficient process. But again it's one of those things, first it might not be possible to realize it because you're working in a very critical regime with regard to premature detonation of this mixture, and so one of the questions was whether you could produce and control the situation well enough to make this practical? It's an interesting concept. We never did because it took quite an effort, but we probably would have done it if the chemical laser program had continued. Well, now, to leave the chemical laser program for a bit, which was one of the areas where we continued to stay in good contact with the work of the Weapons Lab and their contractors and continued to furnish some important information. The glass laser work proceeded fairly well up to a point. Now, it became apparent to all of us working on glass lasers that the nonlinear process of self-focusing in particular was going to be a major problem, and that was not well understood in terms of exactly how you live with it and defeat it, until the work that was done at Livermore, which was an extension of the work that was originally done at NRL, where the first successful glass laser of any size was in operation, and that work was pursued rather vigorously at Livermore. They ran into self focusing in their early systems. All systems including Kidder's system, all found this too be the major problem, including the system we built at Los Alamos. But our decision was to carry the glass laser program ahead only to the point where it would be a useful tool for the interaction physics, and we originally envisioned building a 1 kilojoule system, and we later dropped that down to four of five hundred jewels as we ran into more and more self focusing problems. But we did set up a useful system and did a great of interaction physics, both with pulses in the 10 to 50 picoseconds domain, and the 1 nanosecond domain, but more in the short pulse, where we could get the higher intensities. We also had set up as part of that program to convert to both the green and the ultraviolet, and we did have the beam running for a year or so in the green, and started doing interaction experiments and had planned to carry that forward into the ultraviolet. In fact, we had a set of converting crystals made up for us, and work was done later at Livermore with those crystals.

Seidel:

Those were KDP crystals?

Boyer:

Yes, they were set up to both double and quadruple, one micron light. And so our plan was clearly to concentrate very strongly on doing interaction physics. We started doing interaction physics also at the HF wavelength, 2.7 microns and of course at the CO2 wavelengths, but it was never our intent to build a larger glass system there because of Rochester and KMS, all pursuing glass lasers. We felt that the interaction physics was still not well enough known and one needed to explore all the different avenues.

Seidel:

But you saw the program at Livermore as essentially more or less continuous.

Boyer:

Yes.

Seidel:

That is, there was not a great discontinuity when the NRL group moves over?

Boyer:

No, it was pretty much a continuation. Initially there was also some CO2 work done at Livermore, but it was on a fairly small scale compared to ours, and I think basically looking at it from the standpoint of adding to the interaction studies, as opposed to pursuing large CO2 systems.

Seidel:

Now, Brueckner's work at KMS, some people have seen this as something that the people at Los Alamos and Livermore, and other places, looked at askance. This is a private organization coming into the business, Brueckner is bringing into it all the information he's gotten from being at IDA, etc. Was there a feeling like this at Los Alamos, that this was sort of an interloper?

Boyer:

Well, I think that doesn't quite describe the situation. I think the situation was the following. Going back to some of the early history, I think it was in 1968, there was a meeting held in Washington to look at the laser fusion, and this was before I really got involved in it. At the time we were starting to think about a program but we had an active program which really started in June of 1969. We were just doing some exploring, looking, and I wasn't aware of that meeting at that time. In this meeting, the general ideas for laser fusion were discussed, and there were some people from the CTR program in Los Alamos there, and Kidder and others from Livermore. Brueckner was one of the principals in that meeting, and Brueckner had I think, partly as a result of that meeting and partly as a result of some work he was doing for DNA, Defense Nuclear Agency, on looking at basically effects, questions which involved interaction of radiation with matter, and some of the hydrodynamic effects that one might see when there was a very intense radiation field. He put the two together and decided that this business made a great deal of sense, and he was aware of the work at Livermore that Kidder was doing, and of course, had worked on weapons physics problems was well aware of all of the technology, and so he saw possibility at once that one might indeed use a laser and get interesting intensities. As a result of these calculations he was doing at DNA, he could use the laser to not only heat up the fuel but to compress it rather strongly, which would speed up the reaction rate, which would be essential if one were going to burn very small amounts of fuel. One of the criteria that one immediately establishes when you start thinking about inertial containment of fusion is that the criteria for being able to ignite and burn fuel; in a thermonuclear sense, you have a certain criterion that's really related to a criterion that's been used in magnetic containment, the Lawson criterion, that says you have to produce energy at a fast enough rate and or a long enough time so that you produce more energy than you're losing by Bremstrahlung, and other losses.

Seidel:

The so-called scientific break even.

Boyer:

Yes. Now, this criterion in magnetic containment fusion was just that the product of the time in which you hold the plasma at a temperature at which it is capable of burning, and the number density of the interacting fuel, is greater than a certain number, and in the case of inertial containment fusion, you can substitute the number for just the actual density in grams per cubic centimeter, and you get a time, which is the time that if you have a dense fuel, which you've ignited, that a rare faction wave can move in to drop that density below a critical ratio to the center of your fuel, and so that gives you what we call a "rho-R" product, the product of the density times the radius which turns out interestingly enough that you want a rho- of about 1 gram per square centimeter, as this comes out, and to get efficient burning, although you can get ignition and some propagation at around .2 or so. Well, Brueckner was able to immediately work this out, and he believed that he was aware of what had been done in lasers, and thought that it made sense to build a big glass laser, and he made some early estimates that indicated that one might be able to go to extremely high densities, and get ignition and burning with a rather modest laser. Now, this, indeed, would be possible if you could realize ideal conditions, but you, as we found out later, run into several problems. One is the symmetry and the stability by which you can compress this fuel, and you can always do this more efficiently if you start with a fuel in a thin shell, whose thickness is small compared to the radius, and can collapse it inwards storing, if you like the energy of the laser being absorbed here into kinetic energy of motion, and later when the shell collapses, to the center the kinetic energy is converted into compression and heating of the fuel. This Brueckner recognized, and he did some calculations bases on his earlier work.

It was an extension of let's say the mathematical technique and calculations that he came up with. And this was indeed attractive. One might do it with very low energy. One thing we didn't go into, he had a connection with the KMS industries and Siegel who he talked with, who immediately seized on this. Siegel was a very optimistic and let's say venturesome man who was not at all reluctant to take real gambles, if he thought there was a possibility of a large pay-off, and he was intrigued by this, and they set up indeed to try and accomplish this. They came up with the idea of how to make real targets. That's one of the things that we did in our program, we had also started earlier, and started worrying about how we'd produce suitable targets for the fusion process, as opposed to just studying the interaction physics. And I'll talk about that later, but we looked at the target problem and came up with some ideas, and these were independently thought of by Brueckner. He came up with a scheme for using little glass microballoons that you could fill with a gas by diffusion. One can always freeze the fuel gas on the inside of the sphere and get a thin shell, an use the laser to implode this shell, so in principle it's possible to build something, that might be feasible. Well, Siegel bought a glass laser from General Electric who had been working on glass disk lasers, also. And organized extremely credible work, I think, in terms of figuring out how to make short pulses. They also looked at the conversion to the green as being prepared to either run 1 micron or shorter, and set up to do experiments. But they were more optimistic, and Brueckner, who is one of the really brilliant theoretical physicists, had never, to this time, little exposure to experimental physics and all the numerous problems that you get into when you start doing experiments.

He was fairly optimistic and I think really believed that, and convinced Siegel, that this thing might really be easy to do, and one might come up with a system that would produce a useful fusion device that was small and compact, and then they got carried away, and they did several things. One, they filed for a whole series of patents. Many of the patents infringed on proven and established techniques that had been developed in weapons physics, weapons effects and so on. So a lot of these patents involved principles and ideas which were long time state of the art in the weapons business but hadn't been patented because they bore on classified programs although not necessarily classified in themselves. And this caused considerable consternation both form a standpoint that some of this work might lead to an understanding or technique which would impact on weapon development, and might release information that the AEC regarded as classified, and that it also could raise some maybe embarrassing questions for the future, if all these patents were allowed. So I think this left the AEC with a very uneasy feeling, that things were getting a bit out of hand in this area, and that actually information gained in their own classified programs might be being used in this process, and the other thing was that the promotion that Siegel indulged in, let's say, was a little strong for many of the people working in the field to accept very well. I think at one time they were actually claiming they were going to have home-sized fusion reactors by 1975 or something, small fusion reactors that would take over power production for utilities. There were some very far-fetched projections being made, and so I think, in part, there was a feeling that there had been unfair taking advantage of work that people within the field were not free to release or discuss publicity, and that secondly, they were going to give the whole field a bad name by over-selling it so outrageously that it would lose any credibility, and so I think it was this kind of a thing, rather than a feeling that it wasn't right to have competition. It was the form in which the competition was appearing.

Seidel:

Well, of course, in a way, it's the subtle nature of the DOE labs or the AEC labs, or ERDA labs, that, as I gather, there is a way of prepatenting information. That is to say, there is, the Patent Office does have a way of taking this stuff, not publishing it as a patent but holding the information.

Boyer:

Yes, they hold it, I think.

Seidel:

And that can serve as the basis for interference with another patent application. One of the interesting things that goes back to Glenn Seaborg and the invention, if you will, of plutonium is this whole problem. You know, what do you do with information generated in the private sector? I mean, Glenn Seaborg and Segre and those people sold this to the government, not for not so nominal a sum but a sum, but in general I think it's an institutional problem.

Boyer:

It is.

Seidel:

— that is expressed, and the way, where I got I suppose the way in which I phrase this is from reading Joan Bromberg's book, FUSION. She had picked this up in talking to various people, that there was an uncomfortable feeling. I'm glad you brought up the patent business, because one of the things that is crucial to understanding off modern science and technology is what patents mean.

Boyer:

Yes.

Seidel:

That's a very interesting business, to me. It's a part of this whole picture we've been talking about in terms of the three actors, one being Livermore, one being Los Alamos, and then KMS fusion coming up rather quickly.

Boyer:

And Rochester, too. Don't leave Rochester out.

Seidel:

And Rochester.

Boyer:

And of course there are many foreign activities also.

Seidel:

I guess KMS fusion tends to stand out because of their success.

Boyer:

Yes, because of their success. They actually did; I would say, very credible work. I think they were always overly optimistic and I think pushed their claims pretty hard, and — but I think one should not deny them a lot of credit for very nice work that they did. And it was an example, I think, of going about things in a way that is frequently done in industry almost by necessity, and that is, picking out a sort of limited objective and focusing all the resources and attention on pushing that.

Seidel:

Of course Los Alamos has a bit of this in its history, I mean between 1943 and 1945 they did much the same thing.

Boyer:

Yes, although even in that time there was a tremendous base being built.

Seidel:

Well, you couldn't help it with that group. You began this work in the J division, but at some point in the early seventies, there comes to be an L division, which is probably the result of some entrepreneurial activity on your own part. Could you say something about how that got started before we go further?

Boyer:

Well, let's see. I want to go back and say a little about the CO2 work. And then in the process of doing that, I'll pick up the way the program developed. The laser that, it appeared to me and several others of us, deserved a great deal of exploration, because it appeared that it might be the laser that would best meet the requirements and the practical application of inertial containment fusion, if such were achievable, would be the CO2 laser providing that the wavelength were suitable. We always had the reservation of question about what wavelength would be suitable, or optimum, but we felt that the CO2 laser would do two things. It would give us potentially a very high-powered and high-energy laser that would have other desirable properties, and it would also provide the basic technology that would have to be faced if one found that the CO2 was not the optimum laser because of the wavelength but some other laser medium would be. We felt fairly strongly that for a practical system, for power, propulsion, or whatever, we would need the gas laser system to do that, based on anything we knew at that time, and so we felt it was important to pursue the gas laser, and the best one to pursue at that time was the CO2. We thought the chemical laser could produce these very high energies, but we thought it was questionable that the system could be both efficient, economic and reliable enough to be useful for final application. Our estimates early in 1969, had concluded that we needed lasing volumes cubic meters in size, and operating pressures of three atmospheres or so, and we felt that it should be an electrically pumped laser, because of the simplicity of returning part of the generating power to pump the laser. The first requirement was to start investigating how we could generate what is called a glow discharge, in which you have a diffuse discharge with low electron energy to reduce the energy going in to thermally heating the gas. This is the optimum use of electrical energy to pump the laser and can be very efficient means of creating a population inversion.

Seidel:

Do you know where this came from, the idea of the glow discharge?

Boyer:

The glow discharge was an old phenomenon.

Seidel:

I know, goes back to Townsend and Thomson, but was there any clear technological precedent that you were looking at or was it just the idea of the glow discharge came naturally because of work in gas discharges?

Boyer:

Well, I think we immediately recognized that we would either have to use an electron beam, which is a direct pumping mechanism, or some type of a glow discharge. The required [?] to aperture of an ev or so. Those would be essentially the only two options, and the electron beam had a lot of undesirable problems, we felt, compared to electric discharge. So we set up to see whether we couldn't produce a large volume glow discharge at high pressure, and after looking at various options, we felt that there was a reasonable probability, if we could produce a uniform ionization density to start with that we might get the right kind of discharge, but if it were a self-sustaining one, that appeared to be at best marginally stable, and we felt that if we could supply a continuous source of ionization, that we might indeed be able to establish the right conditions. So we set out to do that, and one technique for doing it we felt was to use X-rays, but that looked like not a very efficient process. We also looked at ultraviolet produced ionization. Both of them appeared less attractive than an electron beam in which the idea would be that the electron beam would only act to produce the ionization, and you could then supply the main energy for the discharge, by a set of electrodes maintained by a low DC voltage.

Ultraviolet ionization appeared promising but we felt that we would have trouble getting uniformity with the ultraviolet, that if you used short enough radiation to get efficient ionization, then the absorption light tended to be restricted in range, and so, we felt that the volume discharge that we could produce would be quite limited. However it appeared an electron beam ought to be, give us satisfactory external source. One, there were some commercial generators that could produce fairly high energy electron beam currents. We felt we could use those as a start, and that we could use maybe an adaptation of the kind of an electron beam generator that's used in the Phermex facility in Los Alamos, which was an X-ray generator. This generates 10 or so MEV electrons with an RF accelerator that then produces a short burst of X-rays for diagnosing explosions. We talked to the people at Phermex and arranged to either borrow a gun from them or build up a gun using one of their cathode assemblies, and set it up to run some tests. We were in the process of getting that together in November, when there was a meeting called by DARPA located in Florida.

Seidel:

At Pratt & Whitney?

Boyer:

No, it was out in West Palm Beach on the coast there, and it was set up to review the various high energy laser and other directed energy techniques, but primarily laser techniques. All the different contractors working on high energy lasers were present and there was a talk given by AVCO at that meeting in which they said that they were generating low pressure, or let's say moderate pressure discharges, of considerable volume, but they planned to pump CO2 lasers, and the pressure I think was about 30 torr or so at that time, that they were working with. They said that one of the problems was maintaining stability, and they had found the trick was to separate, to be able to get control of the ionization process. I think what they said was to get independent control of the conductivity and the electron temperature.

Seidel:

— they weren't talking about an ionizer-sustainer at this point?

Boyer:

I think that was based on the ionizer-sustainer, which was a little different idea, but it's also true that Reilly had thought of this electron beam technique sort of independently, at a fairly similar time to the time we thought of it at Los Alamos and started pursuing it. But their interest primarily was within the lower pressure discharge; for their various applications, they did not particularly need or desire high pressure, whereas for our needs we knew we had to have a high pressure to get the bandwidth, to produce the short pulses, efficiently. So anyway, my surmise at that time, and I speculated to Kidder and others, was that they were using an electron beam to produce their ionization and using that to get independent control of their conductivity and electron temperature because by supplying the electrons from an external beam, you can drop the voltage down to — a point where the discharge is not self-sustaining and it will produce a cold electron distribution. You want cold electrons, around 1 volt electrons, to efficiently pump the CO2, so anyway, it was clear to me that they were at that time working on it, and so we pursued our electron beam. When we came back from there, our group said they thought they had the first E-beam ionized discharge.

Seidel:

This is Fenstermacher?

Boyer:

Yes, Fenstermacher and Merlin Nutter and...

Seidel:

Rink?

Boyer:

Rink, yes. Saying, it's up and running. While Charlie and I were doing the strategy for it, they were actually setting up and running the experimental part. They had what looked like a reasonable result and we set that up and got the first indication then, and then in January we were able to really get the discharge running fairly well and started setting up to probe it to measure gain through the medium, and making sure it was indeed pumping the medium the way we thought it should, and we were able to shortly thereafter generate or demonstrate that we could produce gain up in the 5% centimeter region for pressures of one atmosphere, and soon after that to demonstrate it at three atmospheres. Meanwhile they were working on this at AVCO and came up within actually days or maybe even hours of getting something running about the same time.

Seidel:

I was hoping you could tell me. Nobody else could tell me.

Boyer:

I never paid too much attention to it, except for responding when I was asking questions.

Seidel:

I suppose if these things were fought out in court directly, you would have a patent attorney saying, "You returned from this meeting in Florida with this idea in your head and immediately applied it."

Boyer:

Yes, but of course we had all of our experiments set up before the meeting.

Seidel:

Well, you have notebooks to show that, but what's interesting to me about this whole thing, although I haven't talked to Reilly or Daugherty or anybody at AVCO about it, I talked to Gerry but he was really out of the picture by that time, is that the ideas are really quite similar?

Boyer:

They're really quite similar.

Seidel:

And of course the crude way of looking at this in the history of technology is diffusion, one must influence the other. The more sophisticated way now I guess to look at it is, those elements in the state of the art and the world of ideas which are contributing to simultaneous discovery, and it seems there is in the laser business a good example of simultaneous discovery of devices, this is one, and the chemical laser you can say HF lasers are simultaneous, but the Pimentel laser is a precursor. Here you have a new device coming up in two completely different places, yet, it's sort of interesting to see what was in the air, and I gather from what you have said, that the concepts for exciting carbon dioxide vibrational levels, were fairly straightforward, and if you were going to do it electronically, then you had a choice of these three or a couple of methods that you could use. Conventional glow discharge is out because of the pressures involved, and so you then turn naturally to some kind of electron beam, and you happened to have at Los Alamos a device which could be modified to produce this electronic beam. So that really the breakthrough, if you call it a breakthrough, the invention is something which is not that much of an advance in the state of the art, as it is a combination of existing elements which could come quite naturally to two laboratories at the same approximate time. Is that a fair assessment or would you say that it was a little more than this?

Boyer:

Well, I think that this is generally the case with most inventions. I think the same thing you might say was actually true of the idea of laser fusion. Now, Brueckner thought he came up with the fundamental idea there of compressing and heating a plasma with a laser and a system for doing it. I had come up with the idea that putting a number of things together and saying, gee, this is the way to do it, and what we obviously have to do is get high density, and we have to take advantage of several different things and develop the laser but we've also got to go beyond that, if it were going to be a useful laser that will meet all these requirements. I hadn't actually seen any of Kidder's work on the fusion. I found out a lot about them after we started looking at it, but I also found that Basov and others in the Soviet Union had been working on it or quite some time and so on. I think in general what happens is that when the technology reaches a certain point in awareness, people put the ideas together. I think one of the key things that stimulated a lot of this development was the idea of mode locking a laser, being able to produce very short pulses of very high intensity. There are other techniques you can use now for accomplishing that same thing, but I think it was that sudden realization that there was this kind of energy density available, for the first time, that you could get an extremely short pulse, that made all these things attractive, and then you start looking for ways to get that high density and put other things together. So it isn't often that an invention is something that just comes all alone out of nothing. It's putting several things together and suddenly seeing that this makes a coherent picture. I think that was the case here.

Seidel:

It's interesting that our patent law assumes the opposite.

Boyer:

Yes, it assumes the opposite.

Seidel:

The other interesting feature of this particular one, and as you say, it's quite true that most ideas fall out or condense out of a pre-existing atmosphere of ideas and technologies, but the other think that strikes me is communications. Here you put in this crucial West Palm Beach meeting, a place where you could communicate about classified or work that was classified or proprietary, and so, you know, here the communication seems to have been OK, as one would expect in the scientific community in general. If there was any interference, it was simply that Reilly was not prepared to talk about the details of a process which AVCO considered proprietary. Then I can turn the question around a say, would you go to Reilly and tell him what you were doing at Los Alamos? Or was this one of those things where you didn't know the guy well enough to really talk about it?

Boyer:

Well, to a certain extent it was clear that the people at AVCO felt under some restriction, let's say corporate restriction or direction, in terms of what they would release on an idea that they were still working on and hadn't proven. I think if they had actually demonstrated it and felt confident, then, in what they had, then they might have been willing to have told what they had, but I think you will generally find, where people are in the process of exploring an idea and they're not sure whether it's going to work or not, they are much less inclined to discuss the thing openly than if it's something they have succeeded in doing and know is going to work. There was that evening, after the meeting, a dinner, and I'm trying to think who — I had a conversation with somebody from AVCO and I said to him, "Well, I think I can tell you what your technique for separating the conductivity and the electron temperature is. It's the use of an electron beam to produce an external source of ionization, because we have been looking at that ourselves." And he said, "Yes, that's right." So.

Seidel:

Do you remember who it was?

Boyer:

I'm not sure who that was. I think it was Evan Pugh but I'm not completely sure. That's my recollection now, Evan Pugh I said that to.

Seidel:

Yes, he was a member of that team.

Boyer:

But anyway, there was that much of an exchange at that time. Now, subsequent to that, why, I discussed some of our experiments with somebody at a subsequent meeting at AVCO, and I guess I discussed with Patrick and said that we had been doing experiments, and we were still trying to get the electron density as high as we wanted it, and he said, "Well, we find that we don't need very much. We only need about 1011." I said, "We're trying to get up, we want 1013 or so." He said, "Oh, you can make things work with 1011." I said, "Yes, but you're still working at low pressure, 30 torr or so, and we want to work at several atmospheres pressure." He asked why that was and I said, "Well, because we've got to generate short pulses. We want to generate pulses between 100 picoseconds and a nanosecond, and we need high pressure for that. So therefore we need the high electron density." So he agreed. That was when both of us had succeeded in making our system work.

Seidel:

They were going for somewhat longer pulses, when they got to the pulse.

Boyer:

They were looking for pulses up in the microsecond regime, whereas ours were a thousand times shorter.

Seidel:

So Humdinger and Big Bang and all those weren't really interesting to you at this point.

Boyer:

Not from that standpoint, no. They were just different problems. We would consistently pursue ours and they pursued theirs, and the two were — there was a common technique, but the parameters and the problems are quite different in the two.

Seidel:

I was interested in finding, I guess in Perkins' correspondence at Los Alamos, an account of some visit from AVCO to Los Alamos.

Boyer:

Yes, that was Patrick and Rosa.

Seidel:

In 1976, 1977?

Boyer:

No, it was a little earlier than that. It was around 1974 or earlier, and anyway, what they came for I actually invited them to come I learned in talking with Patrick that they were interested in the possibility of adapting E-beam technology to magneto hydrodynamic [MHD] generators and we said we had the capability but we didn't have any real incentive this time, although I thought of one possible application if we ever got back into the propulsion business that was of interest I said that we had a setup that I thought would be worth investigating to see if we couldn't do a joint experiment. He was saying they had looked at running a MHD system with pure helium and using the electron beam to ionize the medium. Therefore, you expand the working fluid to a very low temperature to get a much greater efficiency out of the system. We had a helium cooled reactor called Utrex which had been terminated because the head of the AEC's reactor division Shaw wanted to put all the reactor effort into the fast breeder reactor, the liquid sodium fast reactor. The Utrex reactor built with the idea of furnishing processed heat for industry to drive chemical reactions. It used a helium loop for the heat exchanger to heat other gasses by convection in order to provide very high temperature processes. Patrick said he thought we could set up jointly a system and check out a very efficient MHD loop using helium ionized with the electron beam heated by the reactor, and he was interested, so he came out and gave a talk on their MHD work and told about the reactor, but the problem was that the wheels had turned too far at that time, for getting the reactor shut down and subsequently dismantled, but I tried to get the program continued long enough to do this experiment and wasn't successful. So that was when Patrick and Rosa came to visit.

Seidel:

I don't know if it was that visit or later, because the —

Boyer:

Well, it may have been later.

Seidel:

I think this was a later visit in fact as I recall Kantrowitz came, but maybe not, anyway, there was a discussion about lasers in general, and I think it was maybe the beginning of the interest in excimer lasers or something at AVCO. My memory is very vague, I have a note which I regret isn't with me, but what struck me about that is, there's a lot of information about, this is what AVCO is like and this is what's going on, as if we didn't know anything about AVCO before, now we have learned these basic things about AVCO, which made me think this was really indirect evidence that whatever was going on at AVCO was not very familiar to the people who wrote this memo in the laser division, which I think was a little after you left the laser division.

Boyer:

Yes.

Seidel:

Which in a way confirms the separation we've been talking about between the development of the two similar lasers at the two different places. The interchange was not rich.

Boyer:

No, and in part I think the objectives were quite different in the two places, and so actually later on, after we had one of our machines going, we visited AVCO and talked with Jack Daugherty and looked at his plans. He had one machine running and was planning larger machines.

Seidel:

Big Bang?

Boyer:

I think it was Thumper he was planning.

Seidel:

I guess there's Big Bang, Big Big Bang, Thumper?

Boyer:

I guess maybe it was Big Bang. Anyway, it was clear we were going along fairly different paths, and actually, we tried to see if we couldn't set up some sort of cooperative venture with AVCO, but it was hard to do at that time. The laboratory's policy at that particular time, tended to be one in which they didn't fund any research outside the laboratory. Now, there were cooperative programs like the Rover program with, a cooperative program with industry, exchange of ideas, but that was different, when both were funded independently out of Washington. It was at a stage when the laboratory had not shifted over to a mode where they were willing to fund another outfit doing research or development for one of their projects.

Seidel:

As I recall, the early seventies was a time when lab size was sort of going down. People were really worried about whether the lab was going to hold together for a while there.

Boyer:

Well, it was, I think, not so much at that time. It contracted a bit subsequently, but at this time it wasn't really contracting, but it wasn't easy to fund new projects without Washington support. Well, I promised to talk about how the laser program, the division was formed and so on. We, as I said earlier, started to work within the J division in the early summer of 1969, where we had a recognized program with a number of people assigned to it, and some number of budget dollars as I remember that first year was probably $150,000 or something. It was not much that year, but it was accepted as a program. In 1970, between the Rover program and the weapons program, I was able to get committed funds for about half a million dollars, I guess, and we started to really lay out a fairly ambitious program with envisioned a lot of different activities, but we didn't really have those well under way until the summer of 1970, I would say, or maybe early fall of 1970, when we got separate efforts going on the CO2 laser, the electron-beam controlled discharge technology, the glass laser and the chemical laser work, and got relations set up with the Weapons Lab, particularly on the chemical laser, to work with us. We were in the beginning of a theoretical effort. It was in the fall of 1970 I think when Bradbury retired, and Agnew stepped in as the director, and shortly after that, Agnew said that he thought that the laser program was an appropriate program for the laboratory to invest some more effort into and he thought it should be organized on a little more formal basis. So he said he would set up a sort of a program office under the director's office, and I outlined what the program might be and the different areas we wanted to pursue.

He made that decision and he appointed me as assistant director for laser activities, I think it was called, or something like that, with a charter to get these programs set up on a formal basis, with people actually assigned to them, and I did that by just asking the different divisions to help out, assign certain people who were already working on it, and make it clear to them that they could really spend their full time on it. So we organized and actually set up the glass laser program, the CO2, the chemical, some work on target development, and the theory, so in each case we picked somebody nominally in charge of each of those efforts. Bob Bossard joined me to help me get a program set up and organized, and it was, done, on a somewhat formal basis. Then I started talking with the Washington office, of the Division of Military Applications about getting formal support, and we got, I think, in the rest of 1970, an authorization for another half million or so, boosting our program up to close to a million dollars for that fiscal year.

Seidel:

Obviously the support for lasers would logically have come from CTR office, and yet here you are getting money from DMA, which suggests that, one or two things, DMA is raiding somebody else's preserve, or that what we're talking about here is a strong interest on the part of DMA in weapons simulation, using laser fusion?

Boyer:

Well, there were two reasons, I would say, that it was pursued here. First, we saw this as a project going beyond laser fusion, and I was going to get into that shortly. In fact, at the time I talked with Agnew I had proposed that we would not only work on laser fusion but we would like to broaden it to really look across the board at the kind of activity that would be appropriate for Los Alamos in laser development, including looking at laser photochemistry and this could get extended into areas like isotope separation and others; though we didn't at that time have a program yet going into that area, we were definitely thinking of the laser photochemistry, and how we might set up to do something there, sort of a complement to the chemical laser work, turn the process around to use lasers to drive chemistry. But there was another reason, that is, the laboratory had under the Division of Military Applications, where it got the major part of its budget, a charter to spend some substantial amount of budget, by substantial I'm not sure how to put that in terms of percentage now, but some in just pure research, to maintain the kind of personnel capability needed, some to look at forward-looking weapon developments, and there was a question of whether, this technology was going to have to lean very heavily on the weapons technology, in terms of a lot of the physics we were going to investigate which was more closely related to the weapons technology than it was to magnetic containment fusion. There was therefore a substantial amount of money in what was called advanced development that could be used for this [other] kind of activity and there was a great reluctance on the part of the fusion community to have anything to do with any program that might have any classified aspects to it. It was very clear, this might have a strong classified aspect to it. So it appeared that it really would not be appropriate to put it over in the fusion area.

Seidel:

Let me suggest another element which comes to me by looking at the labs and a lot of the correspondence of the labs with AEC and that is, one of the things the Weapons Lab always liked was that they were more unified than places like Oak Ridge and Argonne which tended as time went on to be more and more run from Washington, according to whatever division in Washington was sponsored the program. Pretty soon the director was not in the loop any more. The CTR people were running the fusion programs, and the reactor division people were running the reactor programs, and the weapons lab could always say in the director's meeting, "Aren't we fortunate, most of our money comes from DMA and therefore we have a good grip on what's going on in our lab." I would think one of the reasons that a man like Agnew, if he were wise to this problem, would think about this is that it's much better than to stick CTR's hand over here on this stuff, to keep in DMA since we always work well with DMA. One of the things about DMA is that they never had a huge Washington establishment, as far as I can make out, people who are saying, "All right, you in Lab X, you do this, you in Lab Y, you can complement them by doing this." They always say "You guys set up your own programs and we'll support you, if they are relevant." So there [is] an institutional advantage, I would think, would be operating there, by staying with DMA rather than going to CTR. The other thing you suggest about the secrecy business would explain why Friar Tuck and Sherwood Forest would not object too strongly to a fusion effort. Of course, he was no longer head of the magnetic fusion effort but had a strong hand still I presume at this point. So I can think of that additional reason, why you might have—is here anything to that, do you think?

Boyer:

Well, I suppose there might, although I think it would have been very difficult to set this kind of a program up out of the fusion office. If we did it with them, clearly it would have to be done with the concurrence and budgeted out of the fusion office. And this way, it was a matter of just initially redirecting internal funds. These people we had working on it were already getting paid out of the weapons development pot, and so, it didn't mean any immediate change from the Washington viewpoint. Well, then, we set up anyway what we called a project office, and Bossard joined me as my assistant, and we started laying out the complete program. There was another feature I didn't mention and that was looking at applications, and I did set up a group to really start worrying about what the requirements were, what you'd have to do if any of these developments were feasible. For the second year, 1971, we got pretty well organized, and I think at this time we started interacting fairly strongly with the DMA office, and I think it was in, I'm not sure whether it was 1971 or 1972, I think, when the DMA formed what they called the Laser Fusion Coordinating Committee. Did you run into this?

Seidel:

No. I presume it's the predecessor of what became the Laser Fusion Division in Washington.

Boyer:

Well, yes, it's the precursor of what basically, right. I think that was in 1971, maybe, when they started getting that organized. Then we had regular interchanges with Livermore and Sandia also has a small effort going, and largely again for effects. What they initially set their system up to do was to study the effects of high pressures, produce high pressure impulses and shock waves both for calibrating devices and for studying materials. It was a laser program, a glass laser set up under Garth Gobele and Eric Jones, and they had a small program, and the KMS effort, I've forgotten when that first appeared, I think it was about that time I guess. But none were partners in all this. Anyway there was formal recognition on DMA's part that yes, there was a program, and they were allotting a budget to it.

Seidel:

Can you recall who was then head of this coordinating group?

Boyer:

Well, let's see, I think the chairman was Larry Killian. He and Don Gail were the two members from DMA, and I was a member of it. There was considerable debate whether we could bring in Luben from Rochester, but DMA didn't want to because of the classification, and in fact we had to start the program really as a classified program, and so, this committee met every three months, and by 1971, we got at LASL close to a couple of million dollars, for the year. I think it was something on that order. Then, in early 1972, we proposed to Agnew that the program was getting sufficiently large, and difficult to operate with activities in many different areas, under people working for other divisions who weren't particularly interested in this project, that it would make sense to make it a division, and Agnew agreed, and so in March of 1972, we set it up as a formal division and transferred all the people that were then working on it and interested in transferring over.

Seidel:

How hard was this to do?

Boyer:

All we did was, we transferred them by making sort of a roster list...

Seidel:

— The other division leaders didn't come and say, "You're taking my best man such and such, you ought to be ashamed of yourself?"

Boyer:

No, there was no problem. But we first consulted the individual to make sure that they were interested in transferring. At that time, they were also beginning to phase out the Rover program pretty heavily, and in fact, this was one of the incentives I had for organizing a large effort for the program, was that I could see very clearly that the Rover program was headed towards extinction, and there were quite a few people that could have problems in relocating some of whom were the kind of people who would be very useful in this kind of a program.

Seidel:

I'd like to get a jump on that now — you say "some of them." Let us say that someone at Livermore once said to me that Los Alamos would have been better off if they had, instead of taking all these people out of Rover and making them laser scientists, if they'd done what Livermore did, which was to go out and recruit "the best people in the world" to do their laser work. So, because that has been said, I have to say — now it seems to me, when you say some of these people are — then one of your motivations is to rescue their careers. While one might applaud that from the human point of view, I think it's a good thing to do, and I think from the laboratory survival point of view, what you have to do in a place like Los Alamos — because people don't just move across the Bay to Silicon Valley — that in fact, you might, on reflection, think that maybe there is something to the point that had you been in a position to freely recruit people for the organization from wherever you might have cared to do so, that you might have had a stronger effort.

Boyer:

Well, I think there is some truth in that, but I think it's less strong than you might feel.

Seidel:

Well, I say it from Livermore's point of view. We both know that two labs always cooperate, never compete!

Boyer:

I think we did end up with some people who were less well suited than we might have been able to recruit on the outside. I think we, on the other hand, I think we ended up with some extremely good people that we would have had trouble getting any better on the outside. And I guess, in part, as was true at Livermore to a considerable extent, the program grew internally, but their laser program had an advantage at Livermore in that it was started in the early sixties and grew slowly, with recruiting people actually for that program directly and hiring them as you went along, and Livermore was expanding anyway, and so there was, I think, not that same problem. So I think there is, on the one hand, some justice to that. On the other hand we were in this period actively recruiting people, and it wasn't that easy to get that many good laser people on the outside either, that we found. And for some of the things we wanted, we needed to get some people that were not laser experts but were good mechanical engineers or good chemists or good at various other activities, and not just laser per se. Now, what Livermore did later, after Emmett came there, was to go through and drop a lot of people that they had acquired and they did recruit and hire new people to replace a lot, so they actually went through a winnowing and replacing process at one time, and I think that did strengthen their program. It also caused many problems and didn't always help their program.

Seidel:

And that's what was being spoken of, by my source.

Boyer:

So I think that that is true. Now, the other aspect of that, however, was that Livermore, I think, in all honesty, had had a stronger engineering support and has made engineering a part of their laboratory development to a much greater degree than Los Alamos, and they have been able to take advantage of a strong existing engineering organization within the laboratory that I think has provided better support than we had at Los Alamos. Los Alamos in general as a laboratory has leaned much more to physics and chemistry with more basic research, than Livermore has.

Seidel:

I'm glad to have you make that point because it's interesting to me, the first time this was noticed, the engineering capability, was with the parent company at Berkeley by people moving from Brookhaven after World War II. Those were the two competing labs then. "The one thing these guys (Livermore) have over us is that they're engineers. They have a strong independent engineering capability," — led then by Brobeck of course, who was a great accelerator engineer, and it's interesting that even in the seventies with the Livermore branch —

Boyer:

— that's true today.

Seidel:

And I think that's one of the things — of course Los Alamos was started by the man at Berkeley who was not the — did not hire engineers — Robert Oppenheimer. We are back in the office of Dr. Keith Boyer at the University of Illinois Chicago Circle to resume our interview on November 5, 1984, about laser research and development at Los Alamos.

Boyer:

An area that we haven't discussed so far is the laser isotope separation. I mentioned earlier, I think, that we looked upon the laser program as being a very generally based discipline that would address all problems that might be of direct interest to what was then the Atomic Energy Commission and principally through our work on chemical lasers, we early became convinced that laser could also be used effectively to do both diagnostic and process initiation work, in other words, laser photo-chemistry, and in the process of looking at the different areas, to which lasers could apply, we recognized that one of interest to the atomic energy field was that of isotope separation. We did some thinking about that which was brought to a head I think when I was on one of my frequent visits back to talk with the staff of the Joint Committee on Atomic Energy. Captain Ed Bowser who was on the staff asked me if I had read an article that he and Sy Schwiller were looking at on isotope separation, which was embodied in a French patent, and it was indeed one that we had looked at and thought about, and I informed him that was a field we were interested in and thought was important to pursue. He urged us to come up with a proposal, first, to evaluate this French patent, and secondly to review the technology and he thought it would be appropriate if we proposed a program on it. I talked with several of the AEC Commissioners about this and found a fair amount of enthusiasm to investigate laser isotope separation.

So we had a number of sessions in the laser project at Los Alamos. This was just prior to its being made a division. It was apparent that there were two general approaches that we thought would be useful in the case of something like uranium where one was faced with a very large through-puts, as opposed to more general problems where there are many different physical processes that are applicable, and one would be a molecular process where one excites vibrational modes which can be addressed in the infra-red, and uses that excitation to affect the cross-section for absorption of shorter wave photons which can lead to further dissociation. The other process is the atomic one in which one produces an atomic vapor and uses one or a number of photons to ionize the atomic species of interest, and separate that out then by electrostatic or magnetic means. We did rather little on that process until late in 1972, when we formed the division and had received some encouragement from several AEC commissioners, and in discussing techniques which we might use, one individual in particular in our group Paul Robinson who had originally worked with me on the Rover project, took a great interest in this idea, and we discussed a number of possibilities, decided that the molecular process had a great deal to recommend it, and had a series of discussion sessions in which I think it was Ted Cotter came up with one of the key ideas, that we pursued subsequently.

In looking at molecular processes, one is immediately impressed by the wealth of spectroscopic structures that one encounters, and one of our initial concerns was, whether it would be possible to find a place in the infra-red spectrum where we could get clear-cut distinction between two isotopes which would have a very small frequency difference, because it would only be due to the difference in the mass of the two atoms, and while this is substantial in the lighter elements, in the case of uranium, it's very small amount. Actually according to published data at that time it was on the order of or less than a wave number. We had occasion to discuss this with a member of the Oak Ridge National Laboratory staff, D. F. Smith, and he had done a number of calculations on what kind of vibrational and rotational structure one would expect in uranium, and one finds there is very rich rotational structure superimposed on the vibrational structure. He had calculations that indicated that indeed there was an adequate separation between uranium 238 and 235, if one could remove the bulk of the rotational structure. And Ted Cotter made the observation that one should be able to solve that problem by a gas dynamic expansion much as one uses in the CO2 gas dynamic lasers, to freeze out most of the competing vibrational levels, except the ground state so that their rotational structure did not overlap. And indeed D. F. Smith's analysis indicated that if one were looking at the ground state alone, then one could get a clear-cut separation of the two (in spite of the rotational structure). Based on this, we decided to pursue the molecular structure at greater detail, ended up doing spectroscopy on uranium hexafluoride, and did this in a flowing system where the gas was cooled down sufficiently by the expansion process, to provide a resolution of the spectroscopic details, and based on this, we were convinced that we could indeed excite vibrationally one isotope in preference to the other. Then the question was, can one use that vibrational excitation to select a second photon absorbed probably in the ultraviolet which would permit dissociation of the selected molecule preferentially over the unselected one.

And one idea that I had based on the work we had done previously on gas-dynamic lasers was to set up a flow system in which we used a pulse valve to permit us to explore this regime without flowing an unreasonable amount of material. We were indeed able to identify a set of photons of infrared plus ultraviolet which did give separation factors that we thought could be adequate for a process, and this activity was pursued and directed to a large extent after these initial ideas by Paul Robinson within the laser division, and led subsequently to a major project which we received independent funding for. Livermore at this time was looking at the atomic vapor process, as was AVCO-Everett, and later AVCO in connection with Exxon, the New Jersey Nuclear Company, to explore this atomic vapor process, and ended up with what they felt was a viable commercial process. Livermore continued work on the atomic system and while — we continued on the molecular system—and eventually arrived at a point where we felt that a system could indeed be developed for the molecular process, while Livermore believed the atomic process could also be developed, a study was made of these by the DOE. The biggest single problem in the Los Alamos effort was the fact that the infra-red band required for the first step of excitation a region where there were no adequate lasers, and a great deal of effort went into developing a satisfactory laser for this.

Seidel:

The 16 micron band?

Boyer:

This is the 16 micron band, where the preferred excitation lay. Eventually laser systems, laser schemes were worked out for this, but they proved to be much more difficult to develop than the ones for the atomic vapor system, which were primarily in the visible spectrum, where the lasers are much more plentiful. The other problem that of course caused difficulties in the molecular vapor process is that one can run into competition between cooling far enough to get as high a separation factor as is desired, and still retaining an adequate operational density with the high flow-through that's required, and there were budgetary pressures to select one process rather than continue on both in parallel, and it was, I think, clear that the atomic vapor process, was further developed than the molecular vapor, (primarily because of the easier lasers) but in my opinion, the process selection was probably earlier than was optimum in seeing in the long run which process would be the superior one. But having to make a decision at that particular point, I think it was also fairly clear that the atomic vapor process was ahead.

On the other hand, there have been a number of subsequent developments, both in the isotope field and in other aspects of the laser photochemistry, and we examined, for instance, the purification of silane for semiconductor work and concluded that this could indeed be done by laser photochemistry, and we were investigating a series of diagnostic techniques in which a laser is used to examine a chemical process stream in real time and give information on the composition, temperatures, pressures and other parameters that one needs in order to control and optimize the process, and one of these processes that is still proceeding and appears to have a practical application is in looking at coal gasification processes, where studies are being made on real systems by the Los Alamos group, and with considerable success. And I think this again is one of the early areas of laser applications in the photochemistry area, as a diagnosis rather than process control, because of the relatively high cost of laser photons and the requirement generally for these processes to compete successfully against other chemical techniques. But more efficient lasers can change this in the future, and greatly broaden the range of application in real control of laser chemical processes. We're continuing at the lab a process that I got started some years ago, in which I first supported an effort going on at Stanford along with many others, worked with John Madey on the free electron laser, and it's this laser I think that in the long run offers the greatest promise, in large scale chemical processing, which still will have to be done only on selected compounds—but it appears to offer the possibility of lower capital costs and higher efficiencies than other laser systems. And consequently a much lower photon cost, which is essential in any of these applications. There's one thing you didn't discuss, and that was, what the impact might have been of the work that was being done in 1969 by Basov which produced or claimed to produce neutron emissions from lithium deuteride at the Lebedev Institute, and also the work of I guess Gobeli you mentioned was working on the same sort of thing with deuterium, deuteride neutron emission. Did that have any impact on the laser fusion business?

Boyer:

We were of course aware of the foreign activities, and I would say we were somewhat influenced in both laser development and our fusion work by discussions with both Basov and Prokhorov's groups at Lebedev, and Yamanaka's work in Japan and also the work in France.

Seidel:

We were talking about some of the foreign work and you mentioned I guess the work by Floux at the Atomic Energy Commission in France? (List of names) D. Cognard, L. G. Denoeud, G. Piar, D. Parisot, J. L. Bobin, F. Deobeau, and C. Gauquignon.

Boyer:

Yes. And I would say that, in specific answer to your question, we found a lot of the discussions on the laser technology very interesting. We felt that the particular work you referred to by Basov and others about that time, trying to produce fusion, that at least as far as their published experiments and their discussions, they all seemed to have missed the necessity of compressing the material, using the laser energy to compress the material as well as to heat it. They were nearly all based on heating, and so we didn't feel they were particularly interesting, from that standpoint. Now, to what extent it was really true that they had missed the compression or felt restrained in talking about it, as we did at that time, I think is a matter of speculation, and so, I think the fact that they looked upon laser fusion as useful problem to work on, and were getting considerable support, was both interesting to the extent they shed light on the interaction physics as opposed to doing experiments in fusion.

Seidel:

I ran across a talk by James Tuck[1] who spoke in 1969 I think, February 25 is the date either of the publication or the speech, which was about this time, "An Elementary Discussion of the Problem of Producing a Positive Energy Balance from an Inertially Confined DT" in which he explores and reopens the question which you said earlier had been discussed for a long time at Los Alamos, that is a laser as an interesting device to be used, and in this talk, he suggests that now we have reached laser energies at which it becomes an interesting problem once again. Do you remember this talk, anything about it?

Boyer:

Do you remember where this was given?

Seidel:

No. I saw the publication of it in a Los Alamos report which was given as a declassified talk, and subsequently classified because of a "policy change which persists," according to the inside cover. I didn't take extensive notes.

Boyer:

I remember that Tuck did not give a talk at this conference in June, which was actually a Gordon Conference on Laser-Matter Interactions.

Seidel:

This must have been earlier than that.

Boyer:

This was in 1969.

Seidel:

February, 1969.

Boyer:

Oh, then this is earlier. I don't remember that, reading that or hearing that particular talk.

Seidel:

I just, the reason I picked up on it, is Tuck had been leading in magnetic fusion, here he comes out with something about laser fusion, which is one of the earlier.

Boyer:

I think I did talk with Jim on this field and about lasers which might prove useful. (off tape) I know that he felt this inertial containment area was a useful one to explore.

Seidel:

I was curious about it, because obviously it was a talk given at some point as an unclassified talk, and then after a year or so reviewers at Los Alamos got hold of it, they apparently decided that it was hot enough to be classified (not ready to be declassified) and from what you say it may have been the idea of compression which is in there.

Boyer:

If the idea of compression is in there, that's why they — for a while, for reasons that aren't quite clear, the idea of compression was something that couldn't be discussed publicly, and —

Seidel:

And this was basically Brueckner's idea?

Boyer:

No, it wasn't basically Brueckner's idea. This was an idea that Brueckner applied to the problem, but we were all looking at that. At least at Los Alamos and Livermore. That was the essential piece. There was nothing new in that. I'm just saying that when Brueckner thought about it, he came to the conclusion that one could get extremely high compression. Now, the problem of how high a compression you and get is tied in to three different problem areas. One is, whether you can keep from heating the material, the fuel you're compressing, by anything except the adiabatic compression, and this problem is greatly affected by such things as production of hot electrons, or producing of early shocks that can pre-heat the material, and thereby greatly increase the amount of energy required to compress it to a given density. The other problem that has to be considered there is, what is called a Rayleigh-Taylor instability, the fact that you're accelerating an interface and you have both light and heavy material involved, that acceleration can be unstable for a light into a heavy and stable for the other, and you find you always run into an unstable regime in principle when you're trying to compress something like a pellet. The question then is, to what extent you can mitigate this or reduce it by having a very high degree of symmetry to start with, and that implies a very uniform illumination, so there is a requirement of first, not pre-heating the plasma, or the fuel, let's say, secondly illuminating it completely uniformly, and thirdly, structuring the system so that you're working the critical part of the system, the internal part of the system at least, is in a stable configuration. It's the heavy material accelerating the heavy material is unstable, and this is the instability when you turn a glass of water upside down, it goes unstable, and it's really the fact that the light material air producing an acceleration on the heavy material that drives that surface unstable. There's a question then of how stable one can make these systems.

Seidel:

Now, these questions didn't arise immediately?

Boyer:

Well, these were well known questions. Well known. All of them. The only thing is that, the amount of pre-heating, by the hot electrons, was not a known problem. One believed they could probably get very good symmetry, and that by structuring things just right, you might get a stable system. The thinner shell you can make and the larger distance you and accelerate it, the more efficient that is, the higher compression you can achieve, and very optimistic guesses were made by Brueckner and also by John Nuckolls at Livermore. Finally it reached the point where they were estimating that one might get ignition started by as little as 100 joules of laser energy, instead of one have to one megajoule and now the figures have gone even higher, so it was at this low point that some people became very optimistic.

Seidel:

I take it to some extent this includes you, because this is when the program —

Boyer:

I think we always felt that it was going to take, to do anything useful, over 100 kilojoules and all our lasers, I mean our laser development was aimed at that.

Seidel:

The other stream that we talked about that's coming into this is the propulsion studies you were doing. This is of course the paper with Balcomb on fusion powered pulse propulsion systems, one published expression of this is in the 7th Joint Propulsion Specialist Conference.[2] In reading that paper you talk about Orion which we mentioned and also about a project called Beto or Helios. Orion of course is familiar since Dyson published his autobiography DISTURBING THE UNIVERSE. What was Betos?

Boyer:

What was that?

Seidel:

Could you say something about Helios?

Boyer:

Helios, oh, Helios is just the name of a CO2 laser system here at Los Alamos for a long time. And it was original[ly] designed as a 10 kilojoule system, and I guess it finally ran at something around 7 or 8 kilojoules. It got close to the design point. But that was a laser system that at one point we thought might, at 10 kilojoules, approach break even, but the difference between break even and ignition and then a useful system are considerable, each one goes up quite substantially, you see, along with the Helios, we had another system planned that later became Antares. In fact, the current Antares is a smaller version of the original Antares which was supposed to be 100 kilojoules, and that was, let's say, the original planning for that was done back in 1972 or 1973.

Seidel:

OK, now, to get back into this problem of the laser and the interaction, in a presentation you gave in September of 1972 at the Japan-US seminar in Kyoto?[3] I guess you gave it or you sent it there, you mention the need for a shaped pulse in which half the energy is delivered in the last 100 picoseconds, which exceeded the laser technology at that time. I wonder, Nuckolls and Wood I guess had suggested this earlier.

Boyer:

We had all looked at shaped pulses, and Nuckolls and Wood came out with the first publication on this, that was basically because they were able to get a paper through classification that really surprised us. We wouldn't have thought that it would have cleared classification. So they clearly scooped us by a lot. Nuckolls had done more than anyone else on calculating these systems in considerable detail, and developing codes appropriate for calculating them.

Seidel:

So what you're saying is that basically you'd both been working on this problem about the same amount of time. We talked earlier about the need for a more intense pulse, and that the Nuckolls and Wood suggestion was more a matter of publishing priority, than in any meaningful way deriving the concept — the need was pretty straightforward.

Boyer:

Yes. I suspect that if you went back to detailed history, you'd probably find Nuckolls first looked at and may have first proposed some of these ideas, because he started working on these problems in the early sixties, and a lot of this was done prior to the paper, but the point I'm making is that the techniques and so on and the ideas come out clearly naturally out of other developments and out of calculations that you can do. I don't look upon it as a unique invention. See, Brueckner had also come up with the shaped pulse, and they actually worked out a scheme for producing the shaped pulse, and this was certainly done completely independently of Nuckolls, and we were also looking at it earlier. Pollack and others had looked at this. But if you ask, who was the first one probably to look at this and recognize it, I suspect that maybe Nuckolls was the first because he was doing detailed calculations on these systems, with the appropriate codes and techniques, earlier than anyone else.

Seidel:

At Los Alamos you pursued this in a variety of ways, one of which, I guess the most, the one you did the most was saturable absorbers, to help shape pulses, and you worked also with I guess some geometrical means of doing it were considered, and use of other kinds of nonlinear materials. Is there any comment on that? I was basing this on a paper written by James Thorne and Thomas Oree, "Laser Pulse Shaping with Nonlinear Materials."[4]

Boyer:

Well, we did look at quite a number of techniques, and I guess the very first thing we looked at was the technique that either Brueckner or somebody at KMS turned up with, that may not have been Brueckner, I don't know, and that's called pulse stacking. You split your original pulse into a number of pulses and then superimpose them in some scheme that gives you a shaped [?] by delaying and [?], you can build sort of a pulse stacker that will give you any shaped pulse desired. It was clear that one needed something like that. Now, one of those working at Livermore initially in this early period, and later, by several years at Los Alamos was Bob Carman. Now, Carman came up with sort of the ultimate fusion laser scheme, which he never actually tried out. He worked on it for several years and had it a long ways down the road, but never actually demonstrated the final system. The idea was that you start with a CO2 laser, and the iodine laser, and the ruby laser, and you use the ruby laser to pump essentially I guess a parametric oscillator, using lithium Niobate system that starts with a wavelength a couple of microns or so, and you pulse shape it in a very peculiar way, and you use that to drive the iodine system, and the iodine system you drive with the CO2 laser.

He called this a two-photon amplifier, and the final output of this system would use the bulk of the energy from the CO2 laser, but what you finally end up with is the 11th harmonic of the iodine laser. So it starts at long wavelength in microns, and as the intensity builds up, shifts in wavelength continually till at the very peak, (it's a very strongly shaped pulse) it's in the ultraviolet. The theory here is that, first, one of the reasons for thinking that a CO2 laser might have some actual advantages as well as the practical ones of efficiency and scale on which you can build it, is the fact that at the long wavelengths, you find it much easier to get symmetry, and it's clear that in the early stage of driving a pellet the symmetry is the most important at the beginning, so you start with a long wavelength and get the implosion going with a very symmetrical illumination that you can get with the longer wavelengths — but then as the density goes up, the plasma becomes more dense, you need a shorter wavelength to couple in and prevent hot electrons, as you go to the higher intensities, due to the shift to shorter wavelengths you would get a very symmetrical implosion and where the, you needed the short wavelengths the most, you'd have them. He never got a chance really to finish that. He worked on it for several years.

Seidel:

I suppose the real problem would be getting the kind of the efficient frequency shift?

Boyer:

Well, what he would do is essentially drive this iodine system to harmonics and they would act as sort of a harmonic converter.

Seidel:

What was the efficiency?

Boyer:

Well, according to Bob's calculations, experiments he did in iodine and the two photon process, would be efficient. Very efficient. I think if the system worked it might have been a truly efficient stem. It wasn't clear that it would work as designed, but it was an ambitious thing to attempt.

Seidel:

Maybe the most complicated I've ever heard of either. About the E-beam laser, you say that the work that influenced you, in the first note on it which was in 1971 BULLETIN OF THE AMERICAN PHYSICAL SOCIETY.[5]

Boyer:

— Yes actually, I was going to talk almost a year earlier, and I guess in deference to McMahon we delayed the publication. AVCO was giving him a hard time because he wouldn't let AVCO publish, and so we had a paper withdrawn, I mean it was a post-deadline paper, I guess, and this was done to prevent setting up a lot of hard feelings.

Seidel:

This was when McMahon was at ARPA?

Boyer:

Yes, a lot of bickering.

Seidel:

Well, I was going to ask, not so much about that, but just a little citation analysis, that people you do cite are: Beaulieu, LeFlamme and DuMachin's earlier work, not on E-beam lasers, but on TEA type lasers.

Boyer:

Yes.

Seidel:

Is this citation a meaningful one, or just a citation because everybody knows this work and — did this work really influence your thinking in any way?

Boyer:

No, when we were working in E-beam controlled discharge system, we also talked about the possibility of establishing glow discharges by several different ways, and one was the way that, oh, who is it that was, developed, the Canadian who developed that one?

Seidel:

Was that Beaulieu?

Boyer:

Yes. He developed, apparently, he had that fairly well along although we didn't hear about it, and we were trying, we did a lot of point discharge work and that kind of thing, and then we tried to make sort of an asymmetrical conductor based on the way lightning arresters work. Some of the lightning arresters essentially produce a glow discharge, by having two things, first, they use the thyrite material or similar material which has small passages that act as current limiting devices, and when you get a discharge established through them, why, I think the pressure builds up and the resistance goes up so it conducts uniformly over a volume and gives you a glow, and doesn't go over into an arc, so you actually find some of these lightning arresters really are capable of producing a sort of a glow discharge, and we worked on a number of schemes by which we might be able to make electrodes that had the same property but still low loss, and then, both Beaulieu in Canada and Floux in France and others had come up with various ionization schemes in which they do some pre-ionization, but then the discharge has a high enough voltage, to sustain the ionization, and that is a much simpler laser to build. We had reservations from two standpoints. First, it's not nearly as efficient a laser because you end up with a much higher electron temperature in order to keep the ionization going, and also, you dump more energy into the gas in the form of heating and it tends to go unstable after a shorter period of time, and we had reservations about whether one could really do these large volumes we wanted to do, at several atmospheres pressure, with that technique, but I just thought it was important to mention that there were these other types, and maybe somebody would be able to do more with them than we thought they could.

Seidel:

Did you also look into the famous electro-aerodynamic laser? Hill's invention? He was out there at the Air Force Weapons Lab.

Boyer:

Let's see, this is Alan Hill. We talked with Alan Hill a lot, yes. Those looked like very nice things, for one or two things. Either a laser that is running essentially CW or an extremely high pulse rate. Basically it runs more to a CW type laser than a pulse laser.

Seidel:

I just wondered if you talked with him, he's a character down there.

Boyer:

Oh sure. We talked with him a great deal all along, yes.

Seidel:

He has a great fund of ideas, I gather.

Boyer:

Oh yes. Alan's a very interesting person, has lots of ideas.

Seidel:

The other thing that was cited here that intrigued me that I hadn't heard about was, this is actually in a 1972 paper in APPLIED PHYSICS LETTERS,[6] you talk about work by Karl Berger Pearson at National Bureau of Standards which was done way back in the late sixties which suggested "that plasmas could be stabilized if the electron ion production mechanism in the plasma was rendered independent of the applied electric fields through the use of an external ionization source."

Boyer:

Yes. Now, that was after we had actually made the stable discharges, we found that article, and realized that that article did two things. First, it pointed to the fact that this technique would be successful, and secondly, it pointed out an interesting technique for generating electron beams, other than the way we were doing it. On the other hand, if I remember, his discharges were done at quite a bit lower pressure, but we did find that article later on, and we felt it was only appropriate to mention that he had really stumbled on this good idea and demonstrated it before we did.

Seidel:

Well, I was struck by it, because I went and looked at the article, of course, and I said, I haven't heard of this in the AVCO work, I've never seen this cited before, is this really the original idea? You know, I must say, if I read it with the idea that this is the original idea, then I can see it there, but if you just read that article cold, you know, you wouldn't see a very strong connection, I don't think.

Boyer:

Well, I think that may be in part true, because it was after we had succeeded that we found the article and recognized what it was.

Seidel:

The reason why I put the question down though was because I said, gee, here's a new thing, government laboratories working together!

Boyer:

You know, one thing that we argued with AVCO about in this interference, is rather with the lawyers, not directly with AVCO, is that demonstrating that you have a stable system at 30 torr or even 100 torr or so is not demonstrating that it's going to work at one or two or three atmospheres, because there are other problems that can come in, and what one actually finds is that, in these big lasers, if we typically are, pumping time for the CO2 laser was in the range of 1 to 3 microseconds, and if you try and extend that out to 5 or 10 microseconds, somewhere in that region, it often goes unstable and it arcs, even though in principle you don't have a large enough E over P, high enough voltage gradient, for the pressure we're using to sustain, either initiate or sustain the discharge, and the reason that that occurs is something that we didn't recognize for some time. It's called the attachment instability. As you increase the voltage, the attachment rate goes up. It's proportional to E over P. And as the attachment rate goes up, then the number of electrons you have available goes down the current decreases and the voltage goes up, and so, if you have a situation where you have a substantial amount of attachment in the discharge, the current decreases causing further voltage increase until you can get eventually into a regime where you get high enough voltage to actually start producing catastrophic ionization followed by breakdown. And so if you get over into a region that's becoming attachment-dominated it will go unstable on you and break down.

Seidel:

Hadn't Loeb found this out before?

Boyer:

I am not sure. I have looked for it in there, and I haven't found it specifically but I'll bet it's there.

Seidel:

Almost everything is.

Boyer:

Almost everything is. It's easy to get into the attachment-dominated regime, and once you get there, then you're essentially in an unstable regime.

Seidel:

I know that electron distribution is always a real problem.

Boyer:

Yes. I have to go back and refresh my memory — I haven't thought about this for years, but, I remember this. I remember it biting us, figuring out what it was, but it's not always true that you can extrapolate from one regime into another with impunity. You can get into unexpected difficulties, and we often did.

Seidel:

Well, we talked a little earlier about the organization of the division. Now I want to talk a little bit about the micro-organization. And one interesting thing I turned up at Los Alamos, actually, are Phil Mace's old notebooks containing Xeroxes of all the articles he was reading at the time, articles on mode locking and various other things, flash lamps—I just looked through it to see what sorts of things, I don't know where he got the stuff, but in there was a note called "Experiments to be done," from April 15, 1970. This was a meeting of your group. So I thought I'd ask you if you could remember any of this stuff that you were talking about. On April 15, 1970, Phil Mace took a few notes. Just to see if any of it rings a bell. First thing it says was that an announcement was made that as of 4/14, engineering expects to have the building ready for moving the glass systems in five or six weeks. Presumably this is the small glass system, before the 1400 joule ones that you —

Boyer:

— well, it was to go in that building, I think. I'm not —

Seidel:

OK, but you may remember about that time frame when the first glass system was going in, early 1970.

Boyer:

The first glass system was put up in a couple of labs up on the third floor in J division there, on the third floor, and Phil Mace and Dennis Gill put it together.

Seidel:

And now it was to be moved to some other place?

Boyer:

This was an expanded system, a lot of it, and it included a disk system. The original was a pure rod system.

Seidel:

OK, so about that time, now, at this meeting, Charlie, presumably Fenstermacher, announces the development of his detector with a rise time of less than 2 nanoseconds, the installation of a gallium arsenide modulator in the cavity of the low pressure carbon dioxide system to investigate active mode locking, and his optimism that an atmospheric amplifier could be built to produce 10 to 50 J.

Boyer:

That's what?

Seidel:

10 to 50 joules.

Boyer:

Yes, well, our first amplifier, you see, our original CO2 laser was actually a laser chain. It had an oscillator and one, two, three amplifiers.

Seidel:

This was the so-called single-beam system?

Boyer:

Single beam system. And I think, I think what Charlie was talking about this time was the design for the first one of those three amplifiers, and the lower pressure mode locked oscillator system, was one of the ways we originally tried to produce the short pulses. We started out with active mode locking using a gallium arsenide modulator, but we switched over to essentially a Pockel cell kind of switch-out. You generate an acoustic wave that deflects the beam. Well, let's see. I guess we did mode-lock the early ones. Then we also had a pulse switch out.

Seidel:

Yes, you also talk at the same time about some electron beam injection experiments, with the goal of setting 1000 joules output in one nanosecond.

Boyer:

Yes, that would be our first chain.

Seidel:

Which would give a high pumping density and an improvement of 2 to 10 in efficiency over the Canadians. I presume by the Canadians you mean Beaulieu and those people.

Boyer:

Yes.

Seidel:

At this point, this is April 15, 1970, you're still thinking more in terms of the Canadian earlier work.

Boyer:

Yes.

Seidel:

See, it can be done, it can be done. OK, now what goes on is, the next day, then you discuss your experimental program: "What has to be done according to Keith" which I presume is you [missing text?] "is neutron measurements including their velocity. Dick Morse comments on what needs to be measured. 1, liquid light absorption, 2, Bremstrahlung in soft X-ray for electron temperature measurements, 3, neutron measurements. Ray Mjolsness" how do you pronounce it?

Boyer:

Mjolsness.

Seidel:

— "makes plea for focusing efforts on learning about low Z absorption processes, if we are aiming toward getting burn, rather than hitting higher Z targets. Looking at energy transfer from electrons to ions in the burn process is quite different from looking at electron heating for X-ray production." Morse comments "the collective effects are influenced by mass ratio but not 'sensitive' to this. He reports experiments in Germany where hydrogen films are produced by dipping a loop in liquid hydrogen-2 pulling it out, freezing it, then hitting it with the laser." Does that ring any bells? This must be at the time you were assembling this special project office.

Boyer:

Yes.

Seidel:

Morse was the head of your theoretical group.

Boyer:

Yes, Dick Morse was the — well, originally it was shared between Morse and Mjolsness but they didn't get along together.

Seidel:

Obviously, from this document we've looked at.

Boyer:

Yes.

Seidel:

Of course, the one thing that struck me about this is, here is a remarkably free give and take on what we ought to be looking at.

Boyer:

Oh, sure.

Seidel:

An example of team physics sort of being planned out.

Boyer:

I think all of these things are a matter of give and take.

Seidel:

Then it goes on to talk about looking for plasma instabilities, density irregularities, looking at electron excursions by measuring modulations of reflecting light, you may be able to say something about the density of the interactions, etc. which are all again looking at this interaction physics. I guess that what this reflects is the group leaders get together and discuss what ought to be done, and then go out and do it, or was this the entire group at this time? I don't know how many people were there. Somewhere I have I think the record, but there seems to have been about 15 people maybe total, in this meeting.

Boyer:

Yes. These were the principal actors, although I don't know at that time, I'm trying to remember, how many we actually had.

Seidel:

This is very early 1970, spring 1970.

Boyer:

Yes. I suspect we didn't have more than about 30 people working at that time.

Seidel:

But this kind of planning process was continuous?

Boyer:

Oh yes.

Seidel:

You needed to do it this way, have meetings, about that many people, to discuss all the problems.

Boyer:

Yes, what the problems were and all that.

Seidel:

By October 1972 which is two years later, Morse had calculated that the absorption of laser energy by plasma at high power densities, and intensities I suppose, would be very strong, and he accounted for this abnormal anomalous absorption, not to be expected because the wavelength effect, as a result of parametric instabilities, resonance absorption, stimulated Brillouin scattering, and relativistic instabilities.

Boyer:

Who was this?

Seidel:

This was Morse, reported in "Laser Fusion Program."[7]

Boyer:

I think Morse was the first one to propose that the resonance absorption would be one of the dominant processes. Morse was an extremely good plasma physicist, a theoretical plasma physicist.

Seidel:

Had he come out of the weapons program into this?

Boyer:

He was in the Sherwood program.

Seidel:

So these sorts of effects give you hope that you're going to get around wavelength effect fairly early on.

Boyer:

Yes. You see, it's an enormously complicated; the kind of thing you should get into, the different instabilities and processes that you can develop at these high intensities, and so at that time at least, the best the theorist could do was to outline what the different ones were, and give some estimate of which ones they thought would be dominant in that, and then we had to set up and do experiments, and the one whose name I haven't mentioned there who was really the outstanding experimentalist was Gene McCall. He also put together his own glass laser system with a short pulse a 20 or 30 picoseconds system, that allowed us the original first interaction studies, and then later extended them to the CO2 laser as soon as he got that running.

Seidel:

Can you tell me how this influenced your program and whether these interpretations were overly optimistic?

Boyer:

Oh, I think we were always too optimistic. In fact, I think in some of these areas, if you weren't optimistic, you'd never get them started in the first place. I think if you saw all the difficulties and problems that you'd later run into, why, facing them at the beginning would be too discouraging.

Seidel:

Well, I'll give you an even better one, that you can comment on or disregard. In your 1973 article in January, in ASTRONOMICS AND AERONAUTICS,[8] this is the first article which is more technical — you discussed the wavelength effect, and you don't refer to these things as you had earlier, at least in prior publication, you say that the hydrodynamic expansion of the plasma might allow collisional absorption in under-dense regions, and that this and other mechanisms might give rise to an anomalous absorption activity near the critical density. Now, I presume other mechanisms are the ones referred to by Morris?

Boyer:

Yes, particularly the resonant absorption.

Seidel:

Now, the resonant absorption, of course, in reading that article — weren't you to some extent whistling in the dark? You know, it seems to me with resonant absorption, you have this theory of yours, the radiation coming in and hitting the sphere obliquely, and that causing some sort of strange mechanisms to go on, to get around these problems. And in reading through, I don't remember the exact wording now, but it seems to me, of the mechanisms proposed, that was the one that sounded least convincing to me.

Boyer:

Resonant absorption, I used to be able to give a really clear picture of exactly why you'd expect it to happen. It has to do with the change in the impedances as you go from an under- to an over-dense plasma, and the fact that the electrons are driven between the over and under dense, and the fact that they're oscillating through this region, is the thing that gives rise to the strong absorption.

Seidel:

Let me ask a few other questions, and see if some of this brings it back. Among other things, you argued in this article that "in the hydrodynamics and compression and heating of fuel by the laser, the region behind the strong compression shock, would find the internal energy equal to the kinetic energy, and imply a term of 8 percent efficiency at 1 micron and much less at the CO2 wavelength of 10 microns, again favoring short wavelengths as in collisional absorption. However, the electron conduction wave can carry energy into the material beyond the critical density and reduce the effect of wavelength. Most off the absorbed energy remains in the expanding plasma."

Boyer:

And actually it turns out that indeed you do get the energy absorbed. The only trouble is that the electrons get to very high energies, which is not so obvious, why they ever get as high as they do. I think they now have some explanation, but they're more complex than I would care to try and explain.

Seidel:

I was wondering if this, there was a man named Kaw, at the Princeton Plasma Physics Laboratory, who was looking into the nonlinear effects of laser propagation in dense plasmas about this time, and I wondered if that was one of the people you were relying on?

Boyer:

What was his name?

Seidel:

Kaw.

Boyer:

Kaw worked with John Dawson, and he did a lot of studies, particularly on the parametric instabilities. He did his thesis under John, I think. John is one of the outstanding plasma theorists.

Seidel:

So you were relying on things like this, or at least Morse was, in trying to think of ways to get around the problem of interaction problems at long wavelengths.

Boyer:

Yes.

Seidel:

Now, I have another reference here to a paper by a Friedberg and Morder.[9] Friedberg is another who was with your group.

Boyer:

Yes, right.

Seidel:

Who wrote a 1971 report called "Laser Induced Plasma Instability,"[10] and that was one of the mechanisms that was involved here. Another was the business of driven collisional heating, which Mjolsness and Ruppel came up with, and the postulated that the driven collision heating would dominate electron ion heat transfer processes, and contribute substantially to bringing DT pellets to collisional temperatures. And they again interpreted this as being something that makes CO2 laser absorb much more energy and use that energy than one might suspect.

Boyer:

Actually, you know, even the experiments that McCall and others did, all gave indications that the electron spectrum was much colder than it turned out to be, and that — and I think one of the problems in that was in, well, one I think was in knowing what the intensity dependence is, it's sharply dependent it turns out on the intensity, and the other part of that problem was knowing what, precisely what the intensity was. But anyway, the measurements were indicating that the effective temperature, at the intensities we thought we were going to operate with, was only in the 30 to 50 kilovolt range, and that we could live with at 10 microns and we would be all right. It turned out that the electron energies were considerably higher than that, and I think that was partly an intensity problem, but that was really put to rest finally no more than four years ago or so, I'd say.

Seidel:

Well, let's not put it to rest as historians —

Boyer:

No, but I just thought it was interesting, you know, that we were doing experiments and there was a great deal of very good experimental work done, but the point I'm trying to make is that the experiments were hard to do, and the techniques hard to develop, and so event the experiment measurements early on, gave misleading answers to what we eventually determined to be the case. And so it was, while there were always questions about the long wavelengths, it was not at all clear until fairly recently. In fact there are still experiments doing on that might permit one to get around some of these problems — I don't know the last one turned out, but there was a fairly recent one aimed at this same problem, using high magnetic fields.

Seidel:

It's interesting to me, I guess because you are basically an experimentalist, that when you talk about theory and you go to the experimental things, indicating you might put a little more weight on the experimental, and there's a third element here that I would also like you to evaluate, as to how much weight you would give these factors, and those were the studies with computer simulation programs. Now, one of the things about the kind of science that was being done here, done at Los Alamos, done at the Weapons Lab, I think not done at that point in time at most universities, was that three things go on. You have theory, which can be anything from back of the envelope calculations to something quite sophisticated. You have experiments, with hardware in the lab. And then you have a third element which I used to think was some kind of theory, and that is working with computers, but now I've been convinced by everybody telling me this for a long time that actually it's another kind of experiment. That is, you set up a simulation. In this case we have the wave, 2-D, two dimensional electromagnetic plasma simulation code, and this was indicating that when the ion motion was factored into the calculations of absorption, this driven heating collisional process, you were going to get an absorption increasing from 20 percent to 50 to 80 percent. I was wondering, at the time, you're sitting there, you're the group leader, and you have these three streams of evidence coming in to you, and you sort of indicated the experimental evidence was one thing that helped you buy the theoretical arguments. What about the simulation codes? What role did they play? Did you put a lot of confidence in them, very little, none at all?

Boyer:

Well, I think we felt the simulation codes, I felt the simulation codes were rather essential, but one had to benchmark them or calibrate them by experiment. I felt that they were indicative of the way to go, tell you the direction to go, what kind of experiments to do, and to give you some feeling for what the consequences might be, but until you did the experiments, you shouldn't place absolute reliance on those. Now, for instance, these early predictions on the energy, the ones that for instance Nuckolls did, which were very elaborate computer simulations, that's what they were... (off tape) ...the conclusions kept changing, and sometimes by many orders of magnitude. And I think what one is dealing with here is an extremely complex set of interlocking phenomena, and the theory or the simulations, either one, are no better than the assumptions you put into it, and you generally have to make some assumptions or neglect certain things or make approximations, and you may have left out something that is vital, and so, I've always felt that one had to rely more on experiments, to use the theory and simulations to guide you, but you didn't place any complete reliance on them Now, I think it's an area that I have disagreed with the approach at Livermore, in that they place much more reliance on their simulations and calculations than anything else, and there is a tendency to develop a very comprehensive set of interlocking simulations and theoretical calculations, and draw conclusions from that, where the experiments are only done to check maybe a single point or something, the validity of the various pieces that have gone into this structure, and often they elect to believe the predictions before they've gone through a test of the combined system — and I feel that's quite a dangerous situation, that often leads one into mistakes, and you find out well down the road that this is too complicated a system to be able to rely that heavily on the simulation. On the other hand, without them you're lost. You don't have a sense of direction, unless you have some pure intuition to go on.

Seidel:

What this reminds me of is the LASNEX code which you got from Livermore and you put on your machine —

Boyer:

— yes —

Seidel:

— at Los Alamos, but you modified it by adding in one of the factors that you were using to explain why the wavelength problem wouldn't be so serious. I forget right now what particular phenomenon that was, that was added to the LASNEX code, which is their code and also describes what they're doing, and plug in one's own assumptions to it, and the danger would be, as you say, forgetting what your assumptions were and taking them as valid once this machine had gone through them and produced this marvelous result.

Boyer:

That code initially was full of problems, and it was, I think, a very good code, but it had a lot of problems. That code itself was developed from a Weapons code called NIXON, and that code was full of things that nobody could remember why they were in there or how they got there in the first place. And some of them didn't belong there, they were solving the wrong problems.

Seidel:

You always have that with computer codes. When you program a computer, you forget what you put in!

Boyer:

But on the whole, that has been a very good code, and it's undergone extensive development both at Los Alamos and at Livermore, and with a lot of exchange of discussions on a lot of occasions.

Seidel:

At AVCO in the late sixties, Wood and Gerry and Camac came up with a lot of computer studies, kinetics of carbon dioxide energy transfer and other things they did for AFWL. Did you use that stuff at all? Was that incorporated in this?

Boyer:

Quite a bit was. I know we used some things from there, and we also had our own group working in making measurements, and as I say, what we generally found was that you always have to make sure that, if you're working a different regime, that you properly modified things, because often you found that things had changed when you did that. But we had a number of very good laser theorists working on the thing, kineticists and —

Seidel:

— were these people drawn from the chemistry, physical chemistry?

Boyer:

Some of them from the physical chemistry, not all of them. There were a couple who worked on it who would have been Javan's students, who joined the project, who were extremely good. In general, I think there has been probably far more work at Los Alamos on the CO2 laser than anywhere else, looking at all the basic parameters, both experimental and theoretical.

Seidel:

Yes, both the kinetic stuff and — has the kinetic stuff been published?

Boyer:

Some of it got published. One was, there was a lot of work on the kinetics done by Bud Lockett and I sort of remember that he had published quite a bit, and I think Wally Leland published also, but there's probably quite a little bit that didn't get published. I don't know. The guy you could ask about that is Wally Leland at Los Alamos. He's done an awful lot.

Seidel:

Because it seems to me one of the most significant things that comes out of this is a tremendously enriched understanding of molecular spectra in this system, and physical chemists like to see that. In the next article which was the August 1973 article,[11] you get quoted all the time, you argue what I guess is the Los Alamos conviction by this time, which is that only electrically pumped gas lasers appear to be capable of meeting any of the requirements of the power reactor, and of those operating today only the CO2 laser might meet the requirements.

Boyer:

Yes, I carefully said "operating today."

Seidel:

The chemical laser was one that you had in the back of your mind?

Boyer:

The chemical laser I thought couldn't just because of the overall efficiency and economy of its operation, and at that time the, I think excimer laser wasn't invented or hadn't been found.

Seidel:

Well, it hadn't been invented, was it by Basov, announced the excimer laser in 1971 and retracted in 1972? There was a premature announcement of the excimer.

Boyer:

He announced something on xenon.

Seidel:

That was like an excimer system.

Boyer:

Yes, it was an excimer system. Now, actually we worked with Maxwell, on some experiments with xenon in which we obtained five joules or so, 5 or 10 joules out of one, electron beam pumped laser.

Seidel:

When was this?

Boyer:

That must have been about 1973, 1974.

Seidel:

So after this article or about the time this article came out.

Boyer:

Yes, no, after that. I set up in, just about 1973 or 1974, I don't know, a group to look at other laser systems, gas laser systems, under Dean Judd, Dean Judd headed that up, and we were looking primarily at excimer lasers, at the time including mercury halides and noble gas halides.

Seidel:

There's one more thing in this article that I want. Again it's this problem of reflection, and here you refer to these experiments with single beam lasers showing the reflection of between 20 and 30 percent of the incident light at 10 watts per centimeter squared, and measurements indicated reflection —

Boyer:

How many watts?

Seidel:

10 watts.

Boyer:

That must be a misprint.

Seidel:

That's a misprint because it must be 1010 watts or something.

Boyer:

Yes, it must be even higher than that, 1014 probably, I don't know.

Seidel:

The next thing you say is "The measurements indicate that reflected energy reached a peak at 1015 watts per centimeter squared and increased thereafter." You also say the preliminary estimate of the electron energy spectrum indicated that less than 1 percent of it consisted of hot electrons outside the tail of the Maxwell energy distribution which might pre-heat the core and prevent compression. I guess this is what we've been talking about. These are the physical measurements we've been talking about.

Boyer:

Yes. The first measurements indicated that there was a hot component, but that it was a rather small component. Later measurements indicated that the most accurate estimate of the temperature might be 130 kilovolts, I guess. And later one found out that that was really not right.

Seidel:

Well, here's another. You'd stated earlier at some point, I guess this was in October, USAEC Lasers Fusion Program, Status of Laser Fusion Research for February 1975,[12] somewhere in the mid-seventies, "While long wavelengths such as 10.65 produce more hot electrons," you now realized this, "due to the longer periods during which the electric field acts on them, the larger ratio between the size of the blowout cloud compared to the core makes the system more tolerant of hot electrons. The effect is limited with wavelength." So now you're saying the hot electrons won't make very much difference.

Boyer:

No, I said, it's more tolerant, I didn't say ignore them.

Seidel:

But you maybe can compare this, Morse at this same time was studying what he called "heat flow driven instabilities," and concluded in the study he made with Mason of "Hydrodynamics and Burn of Optimally Imploded DT Spheres," that the "degraded performance that had been anticipated from the presence of hyperthermal electrons generated at the high peak laser power levels required for optimized sphere implosions. Both the hyperthermal production and precision needs can be reduced by going to larger pellets and correspondingly higher input energies."

Boyer:

That's correct.

Seidel:

And that's the way you were thinking of going at this point?

Boyer:

You gain by the fact that there's just that much more material that the electrons have to penetrate, and so you get built in shielding. And in fact, that is still true. If you go to much higher energies, why, I mean, if you go up into now — I've forgotten where but it would be in excess of 10 megajoules — why, you again find that eventually you would reach a region where the hot electrons are probably no longer important, because of the self shielding. We did a lot of things, took, including looking at systems where one used what we called vacuum insulation, that would essentially stop the hot electrons by electrostatic fields, that you can support over a very large field gradients, over small distances, with a good vacuum for very short periods of time. But one of the things that makes this statement less true is the finding that as the intensity goes up, the temperature of the electrons continues to go up rather rapidly, and that makes it much more difficult. I would say, as late as 1978 or so—we thought that the hot electron problem was something that one could live with.

Seidel:

You could solve it in some way?

Boyer:

Well, no, I mean, that it wasn't that hot compared to what one could stand, because of the size of the pellets that would be implied.

Seidel:

— the evolution sort of goes, first you're worrying about absorbing the energy,

Boyer:

— yes —

Seidel:

— then you find you can absorb the energy, then you find a lot off the energy is going to making hot electrons.

Boyer:

Yes.

Seidel:

So this makes it look bad again. But in the meantime you're developing the systems and you're well under way. OK, we talked about the pellets, making them bigger. According to Fries and Franum,[13] you devised the basic laser fusion target design, which is a spherical pellet of high pressure DT gas at 50 to 1000 atmospheres surrounded by three layers, glass or nickel mandrel 1 to 2 microns thick, an absorber-ablator layer 2 to 10 microns thick, and between them a pusher layer 5/10 to 5 microns thick. You want to comment on the design and the reason for it or have we said enough about that already?

Boyer:

Well, actually, in these designs, one got to fairly complex structures, and I think, if one had a cold enough electron spectrum, which means, based on our understanding today, that you'd probably have to go shorter wavelengths, but one of the designs might work with energies in the few megajoule range. One might still get a surprise, but I think it's more unlikely now that one would. There are many different types of pellet design, including some that are in the classified domain.

Seidel:

Well, yes. My next question is, what were the principal improvements in target design that followed? That might take us a little too much into that area. But maybe there are a few you could pick out that are specifically important.

Boyer:

I don't know. I think it's a matter of trying to tailor things, so, 1, you get good absorption, 2, you optimize the kinetic energy, you put the ablation pressure into the heavy layer that stores up the energy as kinetic energy, and then later delivers it to the fuel while shielding the fuel as well as you can. Now, we looked at systems and developed them as a practical thing to do where you fill these little balloons with a high pressure gas and then freeze it on the outside. What you do is, fill them, freeze it, and you don't seal them, you diffuse the gas in. You heat them up a bit with a laser and they refreeze symmetrically. One of the tricks we learned was first you freeze it and it forms a puddle in the bottom, and sort of a frozen layer there. Then you hit it with a low energy laser pulse, and it melts. The surface tension makes a uniform layer inside. And then you hit it with a very brief pulse so now all the material heats up in the pellet, so it cools back down and freezes again, and now you have conduction cooling, so it freezes in a perfectly uniform layer inside with nothing in the center, or very little in the center, and I think that's what was intended in these particular pellets, probably.

Seidel:

Well, it's interesting, in this publication which is "Laser Fusion Target Fabrication," status report for 1974, there's a whole number of pellet designs, starting with disks that you were using early on.

Boyer:

The disks, they're always just to study the interactions.

Seidel:

But going on to the microballoons and what not. I guess that would be a whole story in itself, target design.

Boyer:

Oh yes.

Seidel:

The laser systems were designed around about 1973, and the four reaction chamber designs that you considered at this time were the wetted wall with the liquid lithium, the rotating lithium cavity or Basov concept with came from Oak Ridge, the ablative or dry wall concept and the magnetically shielded chamber wall. Now, I gather from reading Williams and Williams and Booth,[14] Los Alamos reports on these systems, that the wetted wall was always more or less the favorite design at Los Alamos.

Boyer:

Yes, I think that's probably true. These studies were done for two reasons, first, to understand what the requirements were going to be, if one were to realize the basic energy release, what kind of energy release could you tolerate, what problems, what variables would be important in optimizing the process, and what would be their values, what parameter could one work in, and what are the limitations that might affect the basic process or design of the lasers or the targets and so on.

Seidel:

Now, one particular thing that occurred to me in that regard was the Henderson study[15] where he studied what happens to a laser beam propagating through the lithium vapor.

Boyer:

Yes, that's an example of the kind of thing, because that is something that one obviously had to worry about. So, in fact, some physical process like that might throw out a given concept, or it might say, we have to work with a different wavelength laser, or something, if we are ever going to make this thing work. So that's why one looked at different reactor concepts it's important to know what the parameter space is.

Seidel:

— well, I gather that the wetted wall concept has the advantage, unlike the ablating wall concept, that you don't get as much lithium vapor out of it, is that correct?

Boyer:

That's right, and it can quite effectively protect the wall against the debris and soft radiation.

Seidel:

Where the lithium vortex and the lithium vapor would give you a lot more lithium to work with.

Boyer:

— that could be more of a problem. And of course, it's, the mechanics, the amount of tritium, a lot of other things can be quite different in the two cases, because there's just a lot of things one has to look at. Maybe the magnetic fusion program should have started earlier to look at these system problems. I think for instance, the Tokomak system has not been looked at particularly kindly by the utility companies in the form that's been proposed because of the difficulty in maintaining and servicing the device, as well as problems in building it and getting it into operation. It might be a lot harder than some other concepts. And so I think you want to be aware of those, what your options and your problems are, so I think this kind of study is a reasonable thing to do.

Seidel:

Would you say that Livermore, you were talking about Livermore's engineering capabilities, were they doing these studies?

Boyer:

They didn't put as much effort into this early on, but later they put a great deal of effort into the study off different concepts and they're still doing it.

Seidel:

I wanted to mention this because I don't think you've talked very much about the system design.

Boyer:

Yes, that was part of our so-called applications group. We had tried to lay out a rather broadly based program.

Seidel:

You were still working with glass lasers throughout most of this period, with what was designed originally to be a 1400 joule laser. By 1975, you have a very sophisticated data acquisition system attached to this. With 32 channel calorimetry input, 40 channel integrated photodiode input, into a Nova 840 computer. And I was wondering if you wanted to comment on this, compared to the one that Livermore uses. We did touch on that earlier a bit. And also, could you comment on the computer code that was used in that to model self-focusing in glass laser systems.

Boyer:

Well, I think that I said earlier that Livermore did a more complete study by far on glass laser systems than we did, and the problems and how to avoid them or live with them and to a considerable extent, we leaned heavily on, first, NRL work and then the Livermore work, on that, and we did not see the glass laser system as a mainline effort, but primarily as a tool to study the interaction physics, particularly the wavelength question, and in fact at the time I left the program in 1976, there were other things, I had in place a capability that would permit us to make comparisons of the interaction physics at wavelengths of both the 2.7 microns from H, and the .53 and .25 microns from the double and quadrupled glass laser system, and my intent had been to really pursue those measurements, and try and get a better resolution of this wavelength scaling. And after I let, I think that work was really not carried through, and I think they got rather heavily involved in the CO2 laser experiments, the Helios machine was coming on line and very close to being an operating system, and they were working with the Gemini CO2 laser, so that wasn't pursued. I thought it was a very important area to pursue, and I felt that Livermore was not pursuing it to the extent that they could or should be doing. Actually most of the shorter wavelength work was going on at Rochester, or was in the planning and beginning stages in Rochester, and I thought it was particularly important to run comparative tests in the same laboratory, with the same group of experimenters, because you can often find that when you compare measurements between two groups of experimenters, that conclusions may in part be dependent on their techniques and biases, as well as on the physical phenomena involved.

Seidel:

Is this connected then to the work you were doing with frequency conversion? I noticed that in the early seventies, 1973 particularly, you were looking at several different ways of doing frequency conversion.

Boyer:

Yes.

Seidel:

Pumping secondary laser media, stimulated Raman scattering, and third, harmonic generation in gasses, and by 1975, which is toward the time when you left, this seems to be —

Boyer:

1976.

Seidel:

By 1975, I'm reading now from Skoberne's report,[16] the project was reduced to one, which was secondary harmonic generation studies using KDP, and I just wondered why the other approaches had been dropped.

Boyer:

Because that was the one technique that, if you like, we had in hand, we knew we could get the intensities that were important, and we had the crystals at hand. We actually had a green beam running and we had checked out the ultraviolet beam and knew that we could do the experiments with that, so the others were dropped because they were in part looking at techniques that might be useful in a broader sense, and I was concentrating that work in looking for a new laser medium as opposed to frequency conversion, because frequency conversion in general, except for the doubling and tripling of the glass laser, is not a very efficient process, for the most part.

Seidel:

OK. The next two questions have to do with something we talked about before, the generation of knowledge about energy transfer in carbon dioxide media, and referring here to C. B. Mills' studies,[17] to [ ] studies, and also Dale B. Henderson's studies of electron transfer in gas discharge lasers, which was a computer simulation. I don't know if you want to say anything more about that or —

Boyer:

That was just in preparation for the larger laser. Just some commentaries on what became the Antares laser system, also to help us making sure that the Helios, although Helios was pretty well scoped out by the Gemini, which had a very similar volume, since Helios was just a multiple laser of the Gemini type, but the Antares, it was clear could have a lot off new problems.

Seidel:

Just to make clear to me and to people who may read this historic material, Gemini originally is called the two-beam system.

Boyer:

Gemini was the first two-beam system.

Seidel:

And Antares is what was called the 8-beam system at first.

Boyer:

No, Helios was the 8-beam system. Antares was to have six modules and each module had twelve beams.

Seidel:

Twelve beams, OK. Let's just talk about some earlier systems. The first is the first one kilojoule CO2 EBL—

Boyer:

Yes.

Seidel:

I guess that, is that the two-beam system or [ ] beam system?

Boyer:

Well, the one we actually got up into the kilojoule range was a two-beam system.

Seidel:

OK, now, this particular system was used for interaction studies.

Boyer:

Yes. That was the one beam system.

Seidel:

OK, and this was referred to at some points [as] a joule system but it didn't produce quite that much.

Boyer:

No, it didn't produce quite that much.

Seidel:

OK, now this one gave some new problems, one was self-oscillation and another is target reflection, if you wanted to talk about those. I know that this is going to get into the problem of building isolators to fight parasitic oscillation and target reflection problems. SF6 gas cells, changing aperture sizes.

Boyer:

Where we really got heavily into that was in the Gemini system, that was the two-beam system, where we found that some targets, particularly some of the spherical targets, the gold microballoon, the gold-coated ones and so on, gave enough reflection off the target to make the laser develop parasitic oscillations before it was triggered, and there were also a lot of problems in that. That was the first really large volume system that had both high enough gain and large enough areas to run into a lot of internal reflections. We had to find techniques for making the inside of the laser largely non-reflecting, and we found for instance we could put a fiberglass cloth layer over the anode and break up the reflections due to it effectively, and we found that putting a coating of lithium fluoride sort of fabricated a plasma generated vapor deposit on the inside, gave a sufficiently black surface at 10 microns so that we could stop most of the oscillation, but then we found that we also ran into trouble built into the Helio system. I think we actually put one in the Gemini laser, a separate window and cell in front of the big reflecting mirror, and we did a lot off work on absorber gasses to find an absorption mixture that would absorb on all the lines in both the R and P and Q branches, that it would absorb everywhere, and yet saturate on the lines we wanted to run on.

Seidel:

And this is what the SF6 work was about?

Boyer:

Yes, it was a combination of SF6 and a number of freons and so on. So we were able to solve that problem, and we ran into enough trouble on Gemini, I remember, so that sort of an extra leg was built onto the Helios laser to further reduce that problem, and it was largely successful, but we learned enough so by the time we got to Antares, those problems were pretty well licked. The other thing we [ran] into in the target problem, and this was the thing that limited us in energy in both the one beam and the two-beams and to some extent the Helios, was target reflection, and in Antares we built with a long enough path length so that there wasn't time for target feedback after the gain was established, so that didn't turn out to be a problem in Antares. It was solved. But these problems were fairly severe, because there's a lot of pretty high gain in a large volume system.

Seidel:

Another problem that you ran into was the asymmetry of the implosion, when you were hitting it with one beam, you out that you're not going to get a good implosion. Henderson and McCrory worked on a perturbation analysis of this. In 1974 they claimed, at a conference in Germany, that you could still get ablation stability for non-uniform laser radiation.

Boyer:

Well, originally, one hypothesized that the electron temperature you produced in the ablation layer and outside the ablation layer was sufficiently large compared to the radial transport of energy inward that the electrons would do most of the symmetrizing that was needed of the energy deposition, and as a consequence you would get quite a uniform ablation. It turned out that that transport was not as effective as one suspected, the azimuthal transport was impeded, and this whole business of electron transport was another of the fundamental problems. There were various ideas of what was causing the problem, and there were so-called flux limiting procedures that were put into the calculations, to try and adjust, sort, of almost an empirical adjustment of the calculation to match what was measured. And I think that in part, these effects were later traced to self-generated magnetic fields, which produced non-uniform heat transport as a consequence, because the fields were modifying the electron trajectories, and the combination of the two left if you like, local magnetic gradients that were pretty strong.

Seidel:

Sun spots.

Boyer:

So this was one of the problems, besides the hot electrons and the potential hydrodynamic instabilities, was the lack of adequate thermal transport, all of which had been assumed in the early calculations.

Seidel:

OK. Now, one more thing on the two-beam system. One of the interesting black arts in laser design is the oscillator design, and you went through some iterations of this and finally settled on the three pass off-axis Cassegrainian telescope design, which avoided excessive feedback from diffraction, but had another drawback in that some areas it would support four passes rather than merely three, and you had to mask off part of the mirror to prevent this, and this then restricted the output of energy you could get, to about 400 joules, and in reading this I was wondering why this particular system was selected, firstly, and secondly why you rejected the confocal telescope which had been developed by people like [ ] and Sooy for high energy lasers elsewhere?

Boyer:

You mean the confocal Cassegrain on-axis?

Seidel:

Yes.

Boyer:

I think again it was, I'm trying to remember, but I think it had to do with this parasitic problem, and how one avoided that, remembering that we were working with very very high gains. What we did in the Helios was to have the extra leg so that one could avoid that problem. But I think there was a problem or concern that if you went to a centered confocal system, the Cassegrain system, that you would need another absorber in front of the small mirror, and the only way you could do that is put another full diameter window and gas cell, as I remember, something like that. I remember that we considered that and there was some objection to it in terms of what one could actually get in the system.

Seidel:

Were you using things like Krupke and Sooy's oscillator studies I guess you were just drawing on the general literature in oscillator design as far as this is concerned.

Boyer:

You are confusing oscillators and amplifiers. This is a high gain amplifier you are talking about on Gemini and Helios.

Seidel:

There was one system you came up with, I don't know if you ever used it but you talked about going to it, Gregorian configuration using a broad band solid state saturable absorber. This was to prevent retropulse. Did you actually use?

Boyer:

I remember one problem was that retropulse problem. Now, in a retropulse, what you had to do was to do things so that the main beam going through let an ionized path in front of the one returning to the oscillator, so that it was sort of self-terminating. What I think we had to do was to focus through essentially a spacial filter kind of arrangement, and you created a plasma in there that the beam went through, and then the retropulse coming back saw that plasma still sitting there, and didn't go through, and there was a critical amount of energy that you could feed through, and above that it just cut off sharply. So that whole business and the optics of that system was tied into not only the parasitics but the retropulse protection, and I'd have to go back and refresh my memory on some of that.

Seidel:

Well, I'm sure there's a lot of it in Los Alamos reports that I haven't seen. The next phase was the 10 kilojoule or 8-beam system, which I gather is essentially the same as the two-beam system, the two-beam system is a model of that, but it incorporates some new pulse forming networks, to make them all work together I suppose accurately, computerized switching and data for the same purpose, and a picosecond oscillator. Apparently Javan at this point gets into the picture and designed that for you, is that?

Boyer:

Yes, Javan worked on one, but it wasn't the one I think we put on Helios. I think it was the one develop[ed] for Antares, because I think that's right because what we wanted Antares to do was to run on three different lines, and the original plan was to make it run on three separate lines in each band.

Seidel:

This is from your paper to the U.S.-Japan Seminar, on laser interaction with matter in 1976 where you refer to this and you say that it will give any desired 9 or 10 micron line, so maybe it was designed originally for the EBS?

Boyer:

Well, he designed one and then I think some other people redesigned or used the basis of his design, and made a modified one, and then they modified it still more for the Antares. But as I say, the basic idea that he came up with is, I think, a sound one, but it required some more engineering and also there was more work on the isolation, the pulse switch-out, and the pre-amplifier stages, since we had to split the beam eight ways —

Seidel:

— I gather this is the computerized switching.

Boyer:

Yes, it had wider limits and there was quite a lot of work that went into that front end system. It's a pretty complicated system.

Seidel:

Now, what was the purpose of this? It was just the next step up in scaling?

Boyer:

It was the next step in scaling, and in fact most of the real CO2 information, the really good information, has been taken on Helios. It was a very nice operating laser system. I think it want up to at least 8 kilojoules, and it was one experimenters could run and did run ten shots a day or so and often five days a week, so it was by far the best running large laser system anyone had, I think, anywhere. Sid Singer deserves a great deal of credit for that.

Seidel:

But the original plan was, it's a scaling step and you'll do further target interaction experiments.

Boyer:

Yes, it was the next stage up, and the idea that then one would go on.

Seidel:

The thing that's confusing about the Antares is because the Antares is already, by the time you're beginning to build the 8-beam system, what was then called the high energy laser gas facility, had as you say six lasers, 12 beams per module, 100 kilojoule design, 1 nanosecond pulse. I asked here, were there problems you encountered in scaling the technology to this level?

Boyer:

There were many problems, first in learning how to design and do the diagnostics, how to interpret them, how to build targets. There were initially lots of parasitic and machine problems, and high voltage problems, and alignment problems.

Seidel:

I get the impression I guess that these are mostly now engineering problems.

Boyer:

They were mostly engineering problems, except here were many basic problems in the target, and the very understanding of what was going on.

Seidel:

OK, but specifically in building the machine itself —

Boyer:

Building the machine was more just engineering problems, I would say.

Seidel:

OK, and at this point you're getting a lot of support on mirrors from Y-12 with their diamond-turning and Itek is helping you with the optics. It's a big multi-faceted project by this point, I gather. I don't know if you'd want to pick out anybody who made specific important contributions at that level.

Boyer:

I see. Well, I think there were a lot of developments, like Harschaw, we worked with them to develop the soft windows, and we certainly worked with Y-12 to get this big mirror technology, the diamond turning worked out, and Maxwell Labs, in getting the supplies engineered and built. On the Helios we got a bunch of trailer supplies from EMP and [a] generator the Weapons Lab had, and had Maxwell rebuild them to our configurations.

Seidel:

Was this for the big trestle thing?

Boyer:

For Helios.

Seidel:

Was, the supplies came from the big trestle that they had at AFWL?

Boyer:

I think so. I think that's where they came from. At least we got them through the Weapons Lab, or some facility they were surplusing.

Seidel:

At this time I suppose you were also getting a lot of information out of things like the Laser Window Conferences, the ARPA Program in Laser Materials for High Energy Windows and High Energy Mirrors, making some contributions?

Boyer:

I think we got less help there than you would think. We did get some —

Seidel:

I noticed the Los Alamos were often at the Laser Window Conferences. Laser Damage Conferences.

Boyer:

Oh yes.

Seidel:

Now, in the laser isotope separation program, you were working with two kinds of lasers, one, the infra-red lasers to energize after vibrational freezing these things —

Boyer:

Yes.

Seidel:

The second is the ultraviolet lasers, the short wavelength lasers to dissociate UF6 into UF5 and fluorine. Now, early on, you were looking at some suitable candidates for the infra-red side of things. They included such things as a cadmium selenide optical parametric oscillator, pumped —

Boyer:

Yes.

Seidel:

— by hydrogen fluoride —

Boyer:

Yes, that gave one a beam that one could do the early experiments. It provided sort of a seed beam or later experiments. But the cadmium selanide parametric oscillator was able to generate 16 microns, enough intensity to do some early experiments.

Seidel:

But that was it, they weren't going to be scalable?

Boyer:

No. No, it was the only laser that we could produce right off to actually do experiments with.

Seidel:

OK, there were several others. There was an optically pumped NH3, ammonium ion, an optically pumped CO2.

Boyer:

Yes, that was the bending mode laser —

Seidel:

E-beam pumped CS2 and carbon-14 TEA.

Boyer:

Yes, these are all attempts to produce 16 micron lasers.

Seidel:

But these were not just to do experiments, these were?

Boyer:

No, these were to see if one could come up with a prototype that you could develop into a useful laser system.

Seidel:

At the same time you're putting out a lot of contracts for lasers, new laser systems.

Boyer:

Yes.

Seidel:

You have Lincoln Lab working on the 16 micron CO2 laser pumped by hydrogen bromide. You have Gundersen, whom I happen to know at Texas Tech., working on ammonium ion.

Boyer:

Oh yes.

Seidel:

Wittig working on infra-red laser, molecular laser pumped by electron vibrational level energy transfer from bromine. I gather this was sort of like the ARPA new laser program in the mid-seventies. You just put out a fair amount of money to see if anybody could come up with something?

Boyer:

That's right. We looked at all the possibilities and asked for others to make suggestions and if it looked as if they had a reasonable suggestion, why, we gave them a small contract.

Seidel:

These are all fairly small efforts.

Boyer:

Yes, most of them would range from 50 to 150 thousand dollars, but there were several million dollars worth of contracts, probably.

Seidel:

Yes. I have a list in one of these documents. Now the other candidates are UV photodissociation lasers.

Boyer:

Yes.

Seidel:

Now, the ones I've found mentioned are argon fluoride, krypton chloride, xenon bromide, xenon chloride and xenon fluoride, all ranging between 193 and about 354 nanometers.

Boyer:

Right.

Seidel:

Rare gas halide lasers. Now, as I understand it, you try to develop these lasers, you try to frequency shift them, with stimulated Raman scattering sometimes, and Raman gas cells, to get them to lower wavelengths — you also developed something called a cable-fed rare gas halide laser at Los Alamos, so a lot of candidates also at this end of the business. Anything come out of this of particular importance?

Boyer:

The biggest single one, we gave Rocketdyne a contract to build a big kilohertz xenon chloride laser.

Seidel:

Did it work?

Boyer:

Not very well. That was a, I think that probably ended up in the four to five million dollar contract. Yet, it had a lot of problems, and I think that in all fairness, Rocketdyne was not given an opportunity to really try and get all the bugs out of it. Los Alamos felt that they had to get it to Los Alamos and try and get the thing running, that they'd lose more time trying to get Rocketdyne to get the thing properly than to bring it back and work on it themselves. Whether that was a mistake, I don't know, it may have been, but it had a lot of, shall we say, engineering development problems that needed to be worked out, and it was, I think, maybe not as well developed in the concept and early design stage as it should have been. Again, by trying to push the development a little too fast, because there were these time scales imposed by Washington, that ultimately were controlling, in fact that was one of the big problems. There was still development work to be done on the principal laser systems, the molecular process, that prevented a large scale demonstration. I think in another year, a lot of those problems could have been solved.

Seidel:

The first real evidence I find off a changing view in Washington was in 1977, when DOE says, "We don't want a demonstration program any more. What we want is something that can serve as a tail stripping process for the gaseous diffusion and gaseous centrifuge separation," in other words, take what's depleted and get what's remaining. And I saw the note about that. Somebody at Los Alamos had written across the front of it, "Party line." It's a document by a man named Steven Suchard, called "Advances in Laser Isotope Separation." I gather that this is a kind of a de-emphasis of the laser isotope separation program, saying, "Well, we no longer think it's going to be a competitor to the established systems, we're going to tack it on the end and see what we get out of it." And I just wonder what impact that may have had on what you were doing at Los Alamos?

Boyer:

Well, I think two things happened. First, I think for what one was trying to accomplish, the scale of the program, the budgets were not really not adequate, and the time scales I think were not adequate, and I think at the time there was first a decision made on the uranium program, I think that was a year early, and I think some of the official reviews they had concurred in that and said neither process was ready at that time.

Seidel:

Is this the 1978 review that was done?

Boyer:

I'm not sure when that decision was made.

Seidel:

I know there was a 1978 review.

Boyer:

All of these activities, remember, [have] taken place after I left. I was at that time getting a free electron laser program and others going.

Seidel:

Yes, this is one point to break, is when you leave Los Alamos actively, but I do have a few questions on the work you've been doing since then. One was, you went to MIT, you worked with Javan on a frequency tunable multi-atmosphere gain switch CO2 laser.

Boyer:

No, I went there — to work with Javan on all sorts of different things that he was doing, and to give a few lectures. I went there as a visiting professor, and had a pretty broad assignment.

Seidel:

After you left the laser division, you wanted to refresh, retread, your interests?

Boyer:

Actually, I had talked with Agnew over a period of about two or three years saying that I would like to do something else, that the program was then getting into much more off a large scale engineering effort, and that I had felt that the thing I could contribute most to the laboratory was in looking at new programs the laboratory might undertake and to come up with ideas and suggestions and if some of them looked attractive, then to look for support and get them on their feet and going. In a sense, that's what I had been doing, to a great extent almost since I'd been at the laboratory. I think I started about five major programs. I felt this program was getting to the point where I had less to contribute than I had had previously, and that I might really start looking around at what other things we ought to be looking at down the road. So we had talked about this for several years, and I had proposed to him that as a first step that we transfer the laser isotope program over to Robinson and Jensen, who were by that time doing a major part of its direction, and that we start looking around for somebody to take over the fusion side. And in fact, we looked at quite a few different people, and I thought for a while I had one, that would be a good candidate from the outside. Also it was apparent that the amount of time that one would have to spend with the Washington office would be a major part of one's time and activity, and so we talked about that. I looked forward to the program for about a year before that. My candidate decided against the move and Agnew proposed two people within the laboratory. While I had reservations about his choice off the division leader, I was anxious to start looking at possible new projects as the Assistant Director for Advanced Technologies. I was very happy to switch jobs when I did anyway.

Seidel:

One thing I did want to talk about, while you were at the lab and while you were in the program, you got involved with the high energy laser review group which Cooper set up to sort of integrate the DoD high energy laser effort.

Boyer:

You mean, what was called HELRG. Yes, I was involved in that.

Seidel:

— as a DoD observer, and it occurred to me that you might want to comment on a couple of things, in the three years you were there. One is the kind of exchange of ideas which this group facilitated, and I'm interested particularly in DoD-DOE exchanges; whether you have any observations to make about, based on this and your experience with HELRG on the contrast between the Department of Defense and the Department of Energy laser R&D, in three areas, the first being the heavier reliance on so-called in-house laboratory efforts by DOE, at least up until about 1976. Second, the difference in similar R&D efforts because off the different missions, which we talked a little bit about, and third, the relationship between DOE labs and their contractors and DoD in-house labs and their contractors.

Boyer:

Yes. Well, DOE and DoD had very different philosophies in their operations. The DoD fundamental philosophy is to direct and manage a number of contractors who will actually do the work, and in many cases, the contractors were the ones who end up spelling out many of the program details and even program ideas, in some of the cases whereas the DOE labs had their own responsibilities and do their own development work. I think that for the most part, the DOE laboratories both have been better supported, freer to pursue their objectives without as much direction from the outside or as heavy a program commitment as the DoD laboratories, and this has resulted, I think, in their being able to attract a somewhat higher level of personnel than DoD. Now, there are some exceptions. I think the DoD laboratories at Lincoln and at NRL are both quite respectable laboratories, have a lot of competence, but they do have restrictions placed on them. So the DOE and DoD have not had many programs that really overlapped in the past. The one major overlap that they were born with, if you like, was the atomic energy project and the nuclear weapons production and that was run by an office in Washington that was staffed by military people but acted more as a coordinating group than an actual directing and controlling group. And I found that, in the DoD activity, that there were two things. First, in this committee, it was clear that the three services each had their own axe to grind and their own programs, and I think the amount exchange and cooperation was somewhat less than you might imagine it would be, certainly less than I think you find in the DOE laboratories.

Seidel:

Even between Livermore and Los Alamos?

Boyer:

Including Livermore and Los Alamos, that's right. You'd be surprised to find that there's really a great deal of cooperation between Livermore and Los Alamos in the weapons program in particular now. They have a quite different way of working, and we found out that the contractors, the DoD contractors in general resented the DOE laboratories and looked upon them as competitors, and the DoD looked upon the DOE laboratories as another contractor. And so that was an indication that there wasn't going to be a great deal of overlap. Now, when I took over the job in the director's office, one of the areas that I felt was important to push was a directed energy area, and it was clear to me that in that area, that the DOE laboratories had a lot better capability than the DoD did with their contractors, in certain areas, and that it would be important to try and get some kind of a real cooperation between the two. I had a number of get-togethers with people both in DARPA and DDR&E offices, and also with the DOE division of military applications where I was trying to get the assistant director for what's called national security programs, which includes all the weapons activities, to see if we couldn't get some sort of an agreement established where the DOE laboratories could be more effective in really working on some of these directed energy projects. I tried to get both sides, to prepare a memo or letter of understanding between the two agencies that would recognize the DOE activity and solicit their participation and sort of agree on some ground rules that they'd work on. Unfortunately I was not successful in that attempt.

[1] “An Elementary Discussion of the Problem of Producing a Positive Energy Balance from Inertially Confined DT(U),” February 25, 1969.

[2] “System Studies of Fusion Powered Pulsed Propulsion Systems,” AIAA/SAE.

[3] “High Energy Gas Lasers for Possible Fusion Applications,” presentation at Japan-U.S. Seminar on Laser Interaction with Matter in Kyoto, Japan, September 24-29, 1972, LA-DC-72-1090.

[4] “Laser Pulse Shaping with Nonlinear Materials,” LA-5323-MS (Informal Report UC-34), July 1973.

[5]Charles A. Fenstermacher, Merlin J. Nutter, John [?], and Keith Boyer, “Electron Beam Initiation of Large Electrical Discharges in CO2 Laser Media,” BULLETIN OF THE AMERICAN SOCIETY 16:1 (January, 1971), 41-43.

[6]Fenstermacher, Nutter, Leland and Boyer, “Electron-Beam-Controlled Electrical Discharges as a Method of Pumping Large Volumes of CO2 Laser Media at High Pressure,” APPLIED PHYSICS LETTERS 20:2 (15 January 1972), 57.

[7]Boyer, “U.S.A.E.C. Laser-Fusion Program,” Presentation at European Laser-Fusion Conference in Marly-Le-Roi, France, October 9-13, 1972.

[8] “Laser-Initiated Fusion -– Key Experiments Looming,” ASTRONAUTICS AND AERONAUTICS 11:1 (January, 1973) 28-38.

[9]J. P. Friedberg and B. M. Morder, “Laser-Induced Plasma Instability,” LA-4604-MS, March 1971.

[10]R. C. Mjolsness and H. M. Ruppel, “D-T Heating to Thermonuclear Temperatures by Means of Ion-Ion Collisions in the Presence of Intense [missing rest of citation?]

[11]“Power from Laser-Initiated Nuclear Fusion,” ASTRONAUTICS AND AERONAUTICS 11 (1973), 48.

[12] “Status of Laser-Fusion Research,” IEEE TRANSACTIONS: NUCLEAR SCIENCES (February 1975), 40.

[13]R. Jay Fries and Eugene H. Franum, “Laser Fusion Target Fabrication; A Status Report, 30 April 1974,” LA 5703-SR Rev., February 1975.

[14]James M. Williams, “Laser CTR Studies,” LA 5145-MS, March 1973; Williams and Thurman G. Frank, “Laser Controlled Thermonuclear Reactor System Studies,” LA-5718-MS, UC-20, September 1974; L. A. Booth, comp., “Central Station Power Generation by Laser Drive Fusion,” LA-4858-MS, vol. I, February 1972.

[15] “Laser Pulse Propagation Through Ionizable Media,” LA-5086-MS December 1972, p. 13.

[16]F. Skoberne, comp., “Laser Program at LASL, January 1 – January 30, 1975,” LA-6050-PR, 13-15.

[17]C. B. Mills, “CO2 Gas Laser Studies,” LA-5151-MS, January 1973, supplement, June 1973, and supplement II, September 1973. Dale B. Henderson, “Electron Transport in Gas Discharge Lasers,” LA-5154-MS 1973.4