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 plasma ions of lower internal energy relative to the incident particle distribution. The effects of these kinetic interactions manifest in radiative signatures that are used to probe cooler exteriors of ICF plasmas and bright spot x-ray sources in X-pinches. In this talk, recent work will be presented that focuses on identifying and characterizing nonthermal effects in HED Z-pinches using either wire X-pinch or magnetized liner inertial fusion (MagLIF) implosions. Work was previously presented on noninvasive x-ray line polarization measurements of molybdenum (Mo) X-pinches performed on the UNR Zebra generator, representing the first polarization measurements performed on L-shell Mo X-pinch HED plasmas. We expand on this with new analysis of the relative influence of Maxwellian and non-Maxwellian contributions to the measured line polarization, which enables characterization of the energies of nonthermal electron beams (~4 – 30 keV) driving the polarization. As a continuation of this X-pinch work, a comprehensive study of stainless steel X-pinches was completed to examine the role of the experimental load configuration on nonthermal effects in the plasma source. In this investigation, analysis of x-ray diode signals (> 3 keV) and source size evolution is performed concurrently to showcase the influence of load geometry on the x-ray radiative properties of stainless steel X-pinches, with an emphasis on nonthermal electron beam generation. Non-LTE spectroscopic modeling is applied to K-shell iron (Fe), chromium (Cr), and nickel spectra to infer plasma parameters, while analysis of intensity ratios of analogous hot and cold Fe and Cr line emission provides insight into the plasma opacity. Notable results include production of hotter, thermal K-shell plasmas and intense cold K-shell line emission, with enhanced satellite line emission and nonthermal electron abundance for small-angle X-pinches. Lastly, we examine the role of non-Maxwellian photons on the production of nonthermal K-shell Fe fluorescence in a MagLIF plasma produced on the Sandia National Laboratories’ 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 shell. Summarizing results and application to future work will be discussed.

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*We thank Drs. David Ampleford and Stephanie Hansen of Sandia National Laboratories for their many fruitful discussions and valuable contribution to this work. This research was supported by the NNSA through the Krell Institute Laboratory Residency Graduate Fellowship under DE-NA0003960 and by the NNSA under DE-NA0003877, DE-NA0004133, DE-NA0002954 and DE-NA0003047.

The Talbot Numerical Tool (TNT) code was originally designed to postprocess and analyze Talbot x-ray interferometry images. TNT can separate periodic and non-periodic features in the Fourier space by detecting the main peaks of the interferogram spectra. Simultaneous and independent density information can be generated from the phase-shift, corresponding to the second term in the Fourier series expansion, and attenuation, corresponding to the first term in the Fourier series expansion. Additionally, 2D maps of dark-field can be obtained from the third term in the Fourier series expansion and 2D maps of atomic composition (Z-effective) can be derived in post-processing from attenuation and phase-shift contributions. TNT data analysis can be tailored by the user to fit specific experimental configurations. Alternatively, image processing can be automated for fast and efficient real-time analysis. X-ray Moire images of plasma ablation fronts from laser-irradiated plastic and metallic foils have been obtained with TNT using laser-produced x-ray backlighters and coherent x-ray sources. TNT data analysis has demonstrated versatility and robustness at different levels of noise. To further explore its capabilities, the TNT code has been used with visible and IR interferometry probing pulsed-power driven plasmas. We present TNT as an efficient user-friendly fringe analysis tool for the plasma community. The code has been tested against other freely distributed software and high-accuracy was obtained when probing the evolution of laser-produced plasmas, dense plasma focus, magnetically-driven plasma flows and shocks, and single-wire core expansion.

Data-driven model identification methods, like Weak Sparse Identification of Nonlinear Dynamics (WSINDy), can learn the expected governing dynamics from data under the right conditions. This is potentially a powerful tool when exploring plasma systems, where such methods could be used to bridge physical scales or modeling regimes in a physically-consistent way. Successful PDE identification (i.e., correctly determining equation terms and their numerical coefficients) depends on the types of interactions that occur for a given set of initial conditions as well as the level of noise relative to the problem dynamics. For some initial conditions, the governing dynamics can be recovered at a much higher noise level than others. For ideal magnetohydrodynamics (MHD) test problems there are regions of problem parameter space where WSINDy consistently recovers the expected governing equations, while in other regions unexpected PDEs are recovered. Tools from information theory – in particular, the Shannon information entropy – can capture the changes in data properties that separate these regions. By analyzing how and when WSINDy fails for different regions of parameter space, meaningful and theoretically-backed patterns can be identified. In addition, looking at ensembles of identified PDEs provides insight into alternative equation forms where a single data instance may not. For example, with the Brio-Wu Shock Tube (a low-information test problem) different groupings of terms are identified in a way that clearly corresponds to the plasma properties of the system. Some of these correlations suggest in certain regions of problem space the ideal MHD equations cannot be recovered in their standard form, but can in linearized-like forms.

Understanding the dynamics of magnetized turbulence is crucial to interpreting measurements of, and making theoretical predictions for a variety of terrestrial and extraterrestrial plasma systems. This understanding is challenged by the complex nature of the plasma dynamics, which often feature extremely high dynamic ranges and the need to model plasmas using different approximations across those physical scales. In addition, the interactions between magnetic fields, turbulence, and compressibility allow for complex and non-local exchanges of energy that can only be elucidated through careful modeling and analysis.

In this talk we present recent results from our collaboration's efforts to understand magnetized plasma turbulence using large-scale finite volume simulations, with a particular emphasis on our attempts to understand the transfer of energy across physical scales and between energy reservoirs (e.g., from magnetic to kinetic energy and vice versa). We also describe our development of an open source, community exascale plasma simulation tool, Athena-PK, and our near-future plans to use it to perform 3D calculations of terrestrial plasma devices such as the dense plasma focus and Hall-effect thrusters.