Understanding High Inductance Power Flow for Pulse Shaped Targets on the Z Machine

Abstract

Dynamic materials characterization experiments utilizing pulsed power drivers are key to our understanding of astrophysical phenomenon, high pressure materials science, and high energy density physics. Many of the experimental platforms utilized possess higher dynamic inductances than most present and future pulsed power generators are likely to be designed to accommodate. Developing a quantitative understanding of loss mechanisms for these high dynamic inductance targets is key to high pressure materials characterization experiments on present and future pulsed power drivers. Here we will discuss geometries on the Z Machine with dynamic inductances that start at 3+ nH and grow to 9+ nH over 500-1200 ns, mated to a double post-hole convolute via a single transmission line possessing static inductances between 4 and 9 nH. Experimental data will be presented from streaked visible spectroscopy, x-ray diodes, photon Doppler velocimetry, and Faraday cups placed at various locations inside the anode-cathode gap prior to the target for the purpose of characterizing the vacuum transmission line plasma conditions. Experimental data has informed computational methods including analytical loss models and first principles particle-in-cell simulations, which have proven capable of accurately predicting current loss for a variety of target inductance histories and driving current pulse shapes. This work has significantly improved our understanding of the robustness of pulsed power to high inductance geometries and has advanced our understanding of plasma physics in vacuum power flow.