Twenty Million Amps of Current

Twenty million amps of current, released from a bank of capacitors over 100 nsec and sent into a cage of wires, is converted at Sandia’s Z facility into 1.8 mega-joules of soft-x-ray energy, with a peak power of 200 tera-watts. Thus the Z machine is the highest peak-current pulsed-power device in the world (over nanosecond timescales), and the most potent source of soft x rays (radiation in the 100-10,000 eV range). The total x-ray energy conversion fraction---utility power turned into x rays---is 10-15%, much higher than for any other x-ray source.

This makes the Z machine potentially useful for studying two important transactions: nuclear fusion reactions, maybe for producing commercial power; and the radiation spewing out of nuclear bombs. Owing to treaties, the physics of nuclear weapons cannot be studied directly by explosions but only indirectly by tests such as those at Sandia National Lab with its Z machine.

The newest development in this subject is Sandia’s ability to photograph the sequence in which the tiny array of wires carrying the stupendous mega-amp current implodes (the vaporizing wires are pinched inwards by a huge magnetic field) and forms an x-ray-emitting plasma.

The first surprise, once the dynamics of the event could be unfolded from data recorded with special crystals, was how long the pinched wires survived the ordeal. The series of photos, taken using a separate (weaker) x-ray source to backlight the interaction zone, should allow the Sandia researchers to optimize their wire-array design in order to produce even greater x-ray yields. (Sinars et al., Physical Review Letters, 1 October 2004; contact Daniel Sinars, dbsinar@sandia.gov, 505-284-4809; lab website at www.opp.sandia.gov/pbfaz.html)