Current sheath studies in a co-axial plasma focus gun

Abstract

A co-axial plasma focus device is operated in deuterium gas at ambient pressures from 0·2 to 0·7 mm Hg and condenser bank voltages from 10 to 22 kV. Magnetic probing reveals an axisymmetric parabolic current sheath which propagates down the co-axial tube (steady propagation region) and collapses off the end of the co-axial gun forming a dense plasma focus. The state of the plasma just before the focusing action is very much dependent on the velocity in the steady propagation region. This velocity is experimentally studied and compared with a snow- plough theory. The collapsing phase of the current sheath is studied using high speed framing photography and current and voltage measurements. The results indicate a focus of length 1·5 cm and radius less than 1·7 mm.