Time Dependent Axial Z-pinch Characterization of Argon PRS Shots

Abstract

Summary form only given. Characterization of implosion kinematics is of interest in understanding and optimizing plasma radiation source (PRS) K-shell yield. It also serves to provide input parameters to the modeling of PRS pinch conditions. A measure of the sensitivity of the PRS implosion kinematics to changes in initial conditions is the time and axial dependence of the Z-pinch assembly on-axis and its associated K-shell yield. A relatively simple and routine PRS diagnostic is the so-called zipper array, which can characterize both the time and axial dependence of the pinch assembly (zippering) and the pinch x-ray yield. The zipper array is essentially a one-dimensional (1D), time-resolved imager, typically consisting of a linear array of X-ray power sensors (photo-conductive detectors: silicon diodes or diamonds), viewing the pinch through a transverse slit, with appropriate pre-detector filtering selecting the X-ray detection range of interest. We report here a study on the time dependent axial characterization of the pinch assembly and the K-shell yield for argon PRS shots taken with two different current drives, differing both in magnitude and waveform shape, and with implosion times in excess of 200 ns. The first current driver reached a peak current plateau of about 3.5 MA in 100 ns, which persisted at nearly constant current for an additional ~100 ns. The second driver delivered a nominally linear current ramp exceeding 6 MA in 300 ns. The study characterizes the final pinch assembly under both fixed and varied initial conditions. For nearly identical initial conditions, the data generally show a significant degree of reproducibility in the relative zipper timing, but with some variation in the K-shell yield at a given axial position. Changes in initial conditions can have a significant effect. For example, shots without pre-ionization changed the axial time dependence of final pinch assembly and axial distribution of K-shell yield.