Influence of gas conditions on electron temperature inside a pinch column of plasma-focus discharge

The paper reports on soft x-ray emission from high-current discharges in PF-1000U facility operated at 170 kJ. The discharges at static conditions were performed with pure deuterium (D-2) and a mixture of D-2 and neon (Ne). In shots with the gas-puffing 1 cm(3) of D-2 or a (D-2+Ne) mixture was injected 2 ms before the discharge initiation. Time-integrated x-ray images from a Be-filtered pinhole camera showed that the pinch microstructure depends strongly on gas conditions. In shots with the D-2-, (D-2+Ne)- or He-puffing distinct filaments and hot-spots were observed. Time-resolved x-ray pulses were recorded with 4 filtered PIN-diodes which recorded signals from 2 regions of 3 cm in diameter (at z = 3 cm and 6 cm from the anode). From a ratio of x-ray pulses, measured behind different filters, it was estimated that at the static D-2-filling electron temperatures (T-e) were from 90 eV to 200 eV. At the D-2-filling and-puffing additional x-ray spikes were emitted from hot-spots with T-e twice higher. In shots at the (D-2+10%Ne)-filling T-e was 4 keV. In shots with the (D-2+Ne)-mixture puffing intense hot-spots were formed, and T-e reached 2.2-7.5 keV. At the same conditions filaments were reproducible macroscopically, but hot-spots were irreproducible.