Spectroscopy is a formative utility for noninvasive investigation of high-energy-density (HED) plasma. X-ray spectroscopy is notably valuable for diagnosing HED plasma regimes, where thermal and nonthermal emission features describe "hot" and "cold" plasmas, respectively. Nonthermal effects, in general, describe the interactions of non-Maxwellian electrons or photons with near-neutral ions to generate nonthermal radiative signatures. These X-ray features can characterize low-internal-energy ("cold") plasmas in the exterior of ICF environments and in accretion zones around astrophysical compact objects, revealing conditions such as electron temperature, density, opacity, and elemental composition. In this talk, two projects will be presented on the influence of nonthermal effects on X-ray line emission in two types of pulsed power Z-pinch plasmas. The first project investigates non-Maxwellian electrons in stainless steel X-pinches of different load geometries produced on the Zebra generator at the University of Nevada, Reno. Experimental analysis is performed on X-ray diode signals and X-ray source sizes to showcase the time-dependent properties of the X-ray plasmas. Theoretical analysis includes spectroscopic modeling of K-shell Fe, Cr, and Ni plasmas to infer plasma parameters and comparative analysis of intensity ratios of like Fe and Cr line emission to explore plasma opacity. Notable results include production of hotter, thermal plasmas with enhanced satellite line emission and ~0.5% fraction of nonthermal electrons for small-angle X-pinches. The next project explores non-Maxwellian photons driving production of nonthermal K-shell Fe fluorescence in a Magnetized Liner Inertial Fusion (MagLIF) plasma (beryllium with native Fe impurities) produced on the Sandia Z machine. This is performed with a novel Monte Carlo Radiation Transport code, which employs a screened-hydrogenic atomic data package to self-consistently calculate radiative transfer processes. Numerical radiation transport modeling is performed to investigate the spatial origins of Fe fluorescence, revealing nonthermal line production over a broad region from the pinch axis in the MagLIF liner plasma.
We thank Drs. David Ampleford and Stephanie Hansen for their many fruitful discussions and valuable contribution
to this work. This research was supported by the NNSA through DOE NNSA Laboratory Residency Graduate
Fellowship under DE-NA0003960 and also under DE-NA0003877, DE-NA0004133, DE-NA0002954 and DE-
NA0003047. Sandia National Labs is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
