OBSERVATIONS OF PLASMA DYNAMICS IN A GAS-EMBEDDED COMPRESSIONAL Z-PINCH

A series of experiments carried out in a gas embedded compressional Z- pinch are presented. A de micro discharge of 150 mu A between two coni cal sharp edged electrodes is established to produce a hollow cylindri cal discharge, A few nanoseconds before the application of the main vo ltage, a pulsed laser is focused through the anode onto the cathode. W ith this preionization scheme an initial coaxial current structure is established. H-2 and D-2 at a pressure of 1/3 atm were used as a worki ng gas, The experiments have been carried out using a pulse power gene rator capable of delivering current of up to I similar to 200 kA with a dI/dt > 10(12) AVs. The use of H-2 and D-2 allows the study of disch arges with the same electrical properties, but with different dynamics . At early times this preionization scheme produces a coaxial double c olumn pinch, which as current rises, coalesces into a single column be coming a gas embedded compressional Z-pinch, Diagnostics used are curr ent and voltage monitors, single frame holographic interferometry and shadowgraphy, visible streak camera, and single frame image converter camera. Electron density, line density, pinch radius, and plasma motio n are obtained from the optical diagnostics. It was found that the max imum electron density achieved on axis is greater than twice the expec ted value according with the filling pressure used in the discharges, which contrasts with a traditional gas embedded pinch in which the den sity is lower than the expected value from filling pressure. The expan sion rate of the plasma column is reduced to a third of the observed v alue for the single channel laser initiated gas embedded pinch. These measurements agree with the existence of a central current channel in this new configuration of gas embedded pinch. The experimental results clearly show that compression is achieved with the composite preioniz ation scheme.