Investigation of gas-puffed discharges of the plasma-focus type

Since the final plasma-focus (PF) characteristics depend on the primary breakdown process, influence of the initial gas distribution on the PF formation has been investigated by several authors. To study this question, use has been made of the modified MAJA-PF facility equipped with a tubular 72-mm-diam inner electrode and a 124-mm-diam squirrel-cage-type outer electrode. The two electrodes were 298-mm long, and the pyrex insulator was 72 mm in length. To make possible the gas injection, the inner electrode was equipped with special nozzles and a fast-acting valve powered by an auxiliary condenser. Contrary to the conventional gas-injected coaxial guns, in the present experiment the working gas was directed by the nozzles toward the insulator surface. The main discharge, as fired with an appropriate delay, was supplied by a 48-μF bank charged up to 40 kV. The facility has been operated under different static and dynamic initial gas conditions. For the static pressure mode all the characteristics of the PF discharges have been very similar to those observed for the standard PF facilities. For the gas-puffed operation the discharge current has converted an annular cloud of deuterium into a plasma sheath similar to that observed for PF discharges. The current and voltage waveforms have not discerned from those registered for the conventional PF shots. Time-integrated x-ray observations have proved that during the compression phase there is formed a typical pinch column