Holographic interferometry measurements on a 12-CM diameter double-shell argon gas-puff Z-pinch

Summary form only given. A double exposure, three-reference-beam, holographic interferometer using a pulsed Nd:YAG laser has been developed by HYTech Research for NRL. This interferometer was used previously in plasma-filled-rod-pinch diode experiments. In this work, we report on the implementation of, and initial results from, this interferometer to study the effects on the implosion dynamics and pinch stagnation phenomena associated with varying the initial gas density profile of an 8-cm, shell-on-shell ("1234"), long-implosion-time (200 to 3 ns), neon gas-puff Z-pinch. The pinch is driven by the Hawk generator with a plasma opening switch that provides an ~0.6-MA pinch current in ~75 ns that remains fairly constant for several hundred ns. Additional diagnostics include K-shell XRDs, current monitors, a vacuum voltmeter, and a 4-channel, XRD zipper array. The initial profile is controlled by varying the ratio of plenum pressures in the two shells. We describe the interferometer as fielded on Hawk, and discuss issues with, and solutions for, obtaining high-quality holographic interferograms. We also compare fast-Fourier-transform and phase-stepping methods for analyzing the fringe patterns. It had been shown that the K-shell yield depends on the initial gas profile. In this work, interferograms of the electron-density distribution in the imploding and stagnating pinch are compared for a range of gas profiles keeping the total mass fixed. The interferograms are correlated with radiation traces and implosion radius calculated from both load inductance and snow-plow modeling