Optical observation of the instability in microsecond gas-puff z-pinch plasmas

Summary form only given. The occurrence and growth of fluid instabilities in gas-puff z-pinch plasmas have been investigated by using laser diagnostic systems. A schlieren system was employed to investigate the temporal evolution of the structure in the plasma during the pinch. The z-pinch plasma was driven by a fast bank, which provided a current of 150 kA at 1.55s (T/4). Initially the plasma was formed in a cone shape because of the initial gas distribution. After that, the plasma layer moved toward the z-axis and its shape gradually changed into a column. The thickness of the column remained constant at less than 1 mm during the pinch implosion. Another layer, which was indicated to be a shock front, formed inside the current layer, and propagated toward the z-axis faster than the outer one. After stagnating, this faster inner layer expanded and interacted with the incoming current layer and a disturbance was observed to occur at the current layer. This observation leads one to conclude that in the case of a plasma driven by a microsecond rise time current, the plasma instability is caused by a shock wave which initially formed during the implosion process.