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

摘要

Summary form only given. Since the final plasma-focus (PF) characteristics depend on the primary breakdown process, the influence of the initial gas distribution on the PF formation has been investigated. Use has been made of the modified MAJA-PF facility equipped with a tubular 72-mm-diameter inner electrode and a 124-mm-diameter squirrel-cage-type outer electrode. 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 differed from those registered for the conventional PF shots. Time-integrated X-ray observations have shown that a typical pinch column is formed during the compression phase. Optical observations show that during the rundown phase the plasma sheath velocity amounts to 0.8-2.5*10/sup 7/ cm/s. Simultaneous neutron measurements demonstrated that the neutron yield (Y/sub n/) is proportional to the velocity, just as for the static pressure mode. The highest neutron yield has been obtained with a high pressure, up to 40 atm, inside the valve plenum. The correlation function I/sub x//Y/sub n/ maximum can be shifted by changing the gas-puffing conditions.