EXPERIMENTAL INVESTIGATIONS OF HOTSPOTS IN A LOW-ENERGY PLASMA-FOCUS OPERATING IN HYDROGEN-ARGON MIXTURES

We present experimental results on the investigation of hotspot format ion in PFP-I, a small 3.8 kJ plasma focus device operating in hydrogen -argon mixtures, at pressures from below 0.2 torr upward. A combinatio n of multipinhole and slit-wire Xray photography is used to measure th e characteristic size and temperature of the hotspots, over a range of pressure and gas mixing ratios. Filtered p-i-n diodes and a beam-targ et detector are used to investigate the time evolution of the hotspots , Typical size for the hottest emitting region, at temperatures betwee n 200 and 400 eV, is found to be around 150 mu m, with a typical durat ion of the high temperature phase of the order of 10 ns, In general, t he temperature in the final phase of the time evolution of the hotspot s reaches values which are nearly twice those of the plasma column whe re they are formed. Characteristic size of the hotspots is about half of that of the initial plasma column.