A simple criterion for the snowplowing efficiency of the working gas in a kJ plasma focus

Correlation between the appearance of the second peculiarity in the current-derivative signal and the drop in the neutron yield is observed experimentally in a plasma focus discharge. The time-resolved photographs of the current sheath lead to the conclusion that, at the instant of maximum compression, the main current is shunted by the second current sheath, which is formed from the rest of the gas after the passage of the first one. It is also suggested that the generation of the second current sheath is a consequence of two competing processes: filamentation of the first sheath, which thus becomes transparent to the working gas, and magnetization of the residual plasma by the field of the main discharge current.