Phys. Plasmas 18, 092707 (2011)

Credit: SANDIA NATIONAL LABORATORIES

Among the earliest devices developed to try to harness thermonuclear fusion is the Z-pinch (such as the Z machine, pictured, at Sandia National Laboratories). These devices operate by feeding an electrical current of up to several tens of millions of amperes into a space of just a centimetre or less. They get their name from the fact that the Lorentz force on such extreme currents pinches them inwards to produce plasmas of extreme energy density.

One of the practical problems faced by these devices is that the array of thin tungsten wires needed to seed the plasma at the heart of a Z-pinch must be replaced every time it is fired. This severely limits the repetition rate at which they can be operated. A. G. Rousskikh and colleagues instead use vacuum arc plasma guns to produce an annular cylindrical plasma. Although they operated their device at a relatively modest current of 450 kA through the plasma, the resulting pinch reached a temperature of around four million kelvin — a promising start but still short of the hundreds of million kelvin required to initiate fusion.