Z Machine - Physics of The Z Machine

Physics of The Z Machine

The Z machine uses the well know principle of Z-pinch where the fast discharge of capacitors in a tube causes its collapse towards its centerline, under the influence of Lorentz forces (current, magnetic field, force). Bennet researched successfully the application of Z-pinches to plasma compression. The Z machine layout is cylindrical. On the outside it houses huge capacitors discharging in Marx generators which discharge in about one microsecond. Yonas then uses a system to divide this time by a factor 10, using the dielectric power of water, to enable the creation of 100ns discharges.

But this effort was not successful for Heavy Ion Fusion, by lack of sufficient focalization of the beams, despite the high power used. It was known since a long time that the Lorentz forces were radial but the current flow was highly instable and rotated along the cylinder which causes twisting of the imploding tube therefore decreasing the quality of the compression.

A Russian, Valentin Smirnov, then had the idea of replacing the tube (called “Liner”) by a wire array, to fight the azimuthal flow of the current, and therefore fight the MHD instability. The Angara V facility of the Kurchatov Institute had been built for the same reason: to help simulate and design the second stage of hydrogen bombs and test the effect of high power x-rays on nuclear missiles warheads. The space inside the wire array was filled by polystyrene, which helps homogenise the X-ray flux. Any country developing thermonuclear weapons has its own Z machine, but those not using water lines had long rising pulses (for example 800ns in the Sphinx, the French machine at Gramat). In the UK, the Magpie machine was situated at the Imperial College under Malcolm Haines.

By removing the polystyrene core Sandia was able to obtain a thin one and a half millimetre plasma cord in which 10 million amperes flowed with 90 megabars of pression.