Also called the dense plasma focus (DPF), this is one of the oldest devices invented to create fusion. Because of its simplicity, it is used in small laboratories over the world for instructional research. A diagram is shown in Fig. 10.38. A plasma is formed by discharging a large capacitor between the center electrode and the outer cylinder. An ionization front, shown by the white curve, travels rapidly to the end

at the right. There, the current flows between the electrodes in the crown-shaped plasma consisting of streamers. In the center of the crown is a dense Z-pinch which can reach fusion conditions for a brief instant.

Intense X-rays are generated, and with deuterium for DT, neutrons are produced for 10-20 ns [39]. Both diagnostics and theory are difficult for the DPF, and it is not well understood. Nonetheless, some groups are proposing the DPF for p-B11 fusion. There is interesting physics to be studied in the DPF; but, as with all single­pulse machines, it is not suitable as an energy source.