First Fusion at the Z Machine

First Fusion at the Z machine was announced this week at the April meeting of the American Physical Society in Philadelphia. For the first time, Sandia National Laboratories' Z facility in New Mexico has created a hot dense plasma that produces neutrons associated with nuclear fusion. According to Sandia's Ray Leeper, the neutrons emanate from fusion reactions within a BB-sized deuterium capsule placed within the central target in the Z facility, itself about a third of a football field in diameter. While tokamaks cause fusion reactions to occur by confining plasmas in large magnetic fields, and laser facilities focus intense beams on or around a target, Z applies a huge pulse of electricity (about 12 million joules) with very sophisticated timing. The pulse creates an intense magnetic field which crushes an array of 360 tungsten wires into an ultra-light foam cylinder to produce x rays. Striking the surface of the fuel capsule embedded in the cylinder, the x-ray energy produces a shock wave that compresses deuterium gas within the capsule, fusing enough deuterium to produce neutrons. Sandia researchers measured a yield of approximately 10 billion neutrons, around the expected energy of 2.45 MeV, corresponding to a very modest level of nuclear fusion (about 4 millijoules of energy). The deuterium capsule reached a temperature of about 11.6 million Kelvin and was compressed from a diameter of 2 mm to 160 microns. The whole compression took about 7 nanoseconds. Providing outside commentary, Cornell University's David Hammer said the Sandia group performed pretty much a full set of tests to verify that they had achieved nuclear fusion. The ZR (Z-Refurbished) facility, an upgrade scheduled to go online in 2006, is slated to attempt scaled-up fusion experiments. While the Z approach to fusion is a promising, straightforward, and potentially robust method, researchers caution that they are at the start of a very long road in investigating its feasibility as a fusion power source.