Multiband time-resolved spectra of metal surface plasmas: Comparison of experiment with plasma spectroscopic modeling

Abstract

Summary form only given. In MTF liner compression experiments, MG magnetic fields heat up the inner liner surface during compression, possibly leading to gas or plasma formation and mixing of wall material with the fuel. To investigate the conditions leading to plasma formation from an inner metal liner surface, experiments have been performed on the 1-MA Zebra generator, by passing a fast-rising (1.1×1013 A/s rise rate) current through `barbell'-shaped aluminum (Al 6061) and copper (Cu 101) rods with diameters between 0.5 mm and 2 mm. The barbell shape avoids direct line-of-sight between arcs at contacts and the heated surface under investigation. Plasma formation is observed when the surface magnetic field approaches 2.2 MG for Al.1, 2, 3 The experiment also fulfills a need for detailed experimental data to benchmark radiation-MHD and plasma spectroscopy modeling. The metal plasma is well characterized by UV (266 nm) and visible (532 nm) 2-frame laser shadowgraphy, multi-frame optical imaging, filtered visible4 and EUV photometric measurements, and timeresolved visible and EUV spectroscopy. The magnetic field threshold for plasma formation, the expansion speed, the plasma temperature, and the emissions in visible and EUV bands have been compared with the results of a variety of numerical simulations, both Lagrangian and Eulerian, using several different sets of EOS, resistivity, and opacity tables.5,6 For the first time, a spectroscopic quality radiation transport line-of-sight integration for this Al plasma has been performed. Radiation-MHD modeling results from the MHRDR5 simulation is used as input for PrismSPECT spectral modeling. The line-of-sight integration takes into account the emission, absorption, and transmission of each plasma layer and finally is convoluted with the resolution of the EUV spectrometer. The resultant simulated spectrum compares well with the experimental EUV spectra.