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Laboratory photoionized plasmas driven by a long-duration x-ray flux

Presentation #126.03 in the session “Laboratory Astrophysics Division (LAD): High-energy Astrophysics”.

Published onJun 18, 2021
Laboratory photoionized plasmas driven by a long-duration x-ray flux

Achieving photoionization equilibrium (PIE) in the laboratory is a standing challenge of laboratory astrophysics. This is mainly because performing photoionized plasma experiments driven by a broad band x-ray flux where the atomic physics is in steady state requires a bright and relatively long-duration x-ray source. In turn, laboratory PIE is critical for benchmarking astrophysical modeling codes. We discuss an experiment at the OMEGA EP laser facility where a long-duration, 90eV radiation temperature source is employed to produce and sustain a silicon photoionized plasma for up to 30ns. The x-ray source comprises an arrangement of three copper hohlraums that are driven sequentially in time by three separate 10ns, 4kJ laser beams that produce abroad band x-ray flux for 30ns. The x-ray flux drives a tamped silicon sample that heats and ionizes while undergoing a controlled expansion. Several diagnostics monitor both the performance of the x-ray source, as well as the formation and evolution of the silicon plasma. A fourth laser beam is used to generate an x-ray backlighter to measure the charge state distribution (CSD) of the silicon plasma through transmission spectroscopy. The electron temperature is extracted from the K-shell line absorption spectrum using a novel method developed for laboratory photoionized plasmas that is independent of atomic kinetics modeling1. Observations recorded by firing the backlighter at different times in a sequence of nominally identical experiments show a silicon photoionized plasma in steady state whose CSD is dominated by F-, O-, N-, and C-like silicon ions. Comparison with modeling calculations is also presented. This work was sponsored in part by DOE NNSA NLUF Grant DE-NA0003936. *Present address: Astronomy Department, University of Texas, Austin 1R. C. Mancini et al, Physical Review E 101, 051201(R) (2020)

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