Analysis of new multiple material wire-array experiments on 1-MA generators including the study of hot spots

Abstract

Two different sets of new experiments with wire arrays made from Mo or W (primary material) wires together with a few Al wires (tracer material) are analyzed. The first set of experiments involved nested wire arrays and was performed on the 1 MA COBRA generator at Cornell University. These nested wire arrays consisted of 16 Mo or W wires with equal number of wires in outer and inner arrays and with two wires of the main material replaced by Al wires either in the outer or in the inner array. The second set of experiments was performed on 1 MA Zebra generator at University of Nevada, Reno, with planar wire arrays that consisted of 10-16 W wires with two periphery wires replaced by Al wires. Diagnostics included fast X-ray and EUV detectors, time-integrated X-ray and time-gated EUV/x-ray imaging pinhole cameras, time-gated and time-integrated X-ray/EUV spectrometers, an optical streak camera and laser imaging. The analysis of spatially resolved X-ray spectra shows that L-shell radiation (Mo wire arrays) and M-shell radiation (W wire arrays) originate from hot spots in the imploded plasma, whereas K-shell Al radiation comes from a plasma column that extended between the cathode and the anode. Using non-LTE kinetic modeling, location, sizes, and plasma parameters of various L-shell Mo and M-shell W hot spots are estimated and discussed. It is shown that the electron temperature of hot spots can be 1 keV or more, but it is much less (200-300 eV) in the Al plasma columns.