The need to accurately predict radiation transport in stellar interiors and inertial confinement fusion targets provides a clear motivation for spectral opacity measurements of hot dense plasmas. In principle, laser-driven implosions provide a platform to access extreme plasma conditions (densities ρ>ρ0, electron temperatures Te> 400 eV), hard to reach by other methods. In this scheme, an element embedded in the shell is compressed by capsule convergence and heated by conduction from the central hot spot, which also provides a bright broadband x-ray source for absorption spectroscopy. We present an experimental study of absorption spectroscopy with capsules combining two distinct tracer element layers, respectively, titanium and vanadium, embedded in the plastic shell of direct-drive laser implosions at the OMEGA laser facility. The presented work is one of the scarce studies on absorption spectroscopy in an implosion configuration so far, and the use of two elements simultaneously has the advantage of bringing more stringent constraints on the atomic-physics models underlying our radiation-hydrodynamics simulations. Using two layers at different depths also enables us to characterize and benchmark the simulated density and temperature gradients inside the shell. Comparisons between simulated and measured time-integrated and time-resolved spectra are presented, and a good agreement is found, which validates our radiation-hydrodynamics and atomic physics models. The measurements presented here pave the way toward future opacity studies of elements increasingly relevant for astrophysical applications.

The Z-pinch Network US (ZNetUS) is a consortium of researchers from academia, national laboratories, and private industry, dedicated to advancing pulsed magnetic science, technology, and high energy density physics for energy and national security applications with a special focus on creating the pipeline of next-generation scientific leaders. The National Nuclear Security Administration (NNSA) has recently established a pilot User Facilities program through ZNetUS. This initiative represents a significant stride in fostering academic-led collaborations aimed at enhancing the field of pulsed magnetic science and technology (PMS&T). ZNetUS successfully launched its User Facilities program in 2024 awarding time on the User Facilities. Below is a research summary for the first full year of campaigns, and some guidelines on how to start collaborations and apply for time at the ZNetUS.

We discuss the krypton Heβ line spectrum including Li-like satellites with a spectator electron in n = 2 and n = 3 and detailed line shapes computed using standard Stark broadening theory for hot dense plasma conditions relevant to X-ray tracer spectroscopy of inertial confinement fusion implosion cores. The results show that the interference term in the electron broadening does not produce a significant effect for these satellite transitions. However, the effect of the electric field mixing of the energy levels driven by the ion’s microfield distribution does produce a significant change in the line shape. Level populations calculated with a collisional radiative atomic kinetics model were employed to obtain the photon energy resolved emissivity and opacity using the Stark line shapes, and the emergent intensity distribution was calculated by integrating the radiation transport equation along chords assuming a uniform spherical plasma source. The line spectrum has electron temperature (Te) and density (ne) sensitivity due to the temperature and density dependence of level populations and the density dependence of the Stark line shapes. Hence, this spectrum is suitable for a simultaneous temperature and density plasma diagnostic of implosion cores.

We present first results from a novel experimental platform that is able to access physics relevant to topics including indirect-drive magnetized inertial confinement fusion, laser energy deposition, various topics in atomic physics, and laboratory astrophysics (for example, the penetration of B-fields into high energy density plasmas). This platform uses the x rays from a wire array Z-pinch to irradiate a silicon target, producing an outflow of ablated plasma. The ablated plasma expands into ambient, dynamically significant B-fields (∼5 T), which are supported by the current flowing through the Z-pinch. The outflows have a well-defined (quasi-1D) morphology, enabling the study of fundamental processes typically only available in more complex, integrated schemes. Experiments were fielded on the MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time). On this machine, a wire array Z-pinch produces an x-ray pulse carrying a total energy of ∼15 kJ over ∼30 ns. This equates to an average brightness temperature of around 10 eV on-target.

X-ray spectroscopy is a powerful diagnostic of electron temperature (T e ) and density (n e ) of Inertial Confinement Fusion (ICF) experiments. Mostly, previous applications have been based on K-shell line emission and an argon tracer. However, argon becomes too ionized at electron temperatures higher than 2keV and its line emission weakens. Our research shows that Kr L-shell emission from n=4 to n=2 (from 2700eV to 3200eV photon energy range) is an attractive alternative as a diagnostic of implosion core plasmas with T e in the range of 1 to 3.5keV and n e in the range of 5x10 23 to 2x10 24 /cc. Specifically, Kr atomic number concentrations of order 0.02% produce intense 4-2 lines characteristic of moderate optical depth. We have used the atomic kinetics code ABAKO 1 and PrismSpect 2 to solve the collisional- radiative rate equations self consistently with the radiation transport effect and study the basic properties of the spectrum. In addition, we have employed detailed Stark broadening calculations performed by MERL 3 to obtain the Kr L-shell line profiles. Combining the atomic rates and the electronic level populations obtained with ABAKO and the spectral line shapes from MERL we have created an extensive emissivity and opacity database for the ranges of T e , n e and photon energy of interest. The implosions have been simulated with the 1D Lagrangian hydrodynamics code HYADES 4 for conditions characteristic of a series of direct-drive shots performed at the OMEGA laser facility. Post-processing the HYADES output with the emissivity and opacity database permits to model synthetic data that approximates the expected observations and shows the sensitivity of the spectrum with respect to T e and n e . Also, analysis of the synthetic data demonstrates the usefulness as a temperature and density diagnostic.

Analysis of Stark-broadened spectral line profiles is a powerful, non-intrusive diagnostic technique to extract the electron density of high-energy-density plasmas. The increasing number of applications and availability of spectroscopic measurements have stimulated new research on line broadening theory calculations and computer simulations, and their comparison. Here, we discuss a comparative study of Stark-broadened line shapes calculated with computer simulations using non-interacting and interacting particles, and with the multi-electron radiator line shape MERL code. In particular, we focus on Ar K-shell X-ray line transitions in He- and H-like ions, i.e., Heα, Heβ and Heγ in He-like Ar and Lyα, Lyβ and Lyγ in H-like Ar. These lines have been extensively used for X-ray spectroscopy of Ar-doped implosion cores in indirect- and direct-drive inertial confinement fusion (ICF) experiments. The calculations were done for electron densities ranging from 1023 to 3×1024 cm−3 and a representative electron temperature of 1 keV. Comparisons of electron broadening only and complete line profiles including electron and ion broadening effects, as well as Doppler, are presented. Overall, MERL line shapes are narrower than those from independent and interacting particles computer simulations performed at the same conditions. Differences come from the distinctive treatments of electron broadening and are more pronounced in α line transitions. We also discuss the recombination broadening mechanism that naturally emerges from molecular dynamics simulations and its influence on the line shapes. Furthermore, we assess the impact of employing either molecular dynamics or MERL line profiles on the diagnosis of core conditions in implosion experiments performed on the OMEGA laser facility.

The major goal of this project was to study the atomic and radiation physics of photoionized plasmas driven by a broadband x-ray flux and its impact on plasma x-ray heating and ionization, emissivity and opacity, and radiation-hydrodynamics. This problem is relevant to the physics of accretion disks surrounding black holes, x-ray binaries, and active galactic nuclei in astrophysics. In addition, it is also important for understanding non-equilibrium laboratory plasmas driven by a distribution of photons. To this end, and motivated by previous and ongoing gas-cell experiments performed by the PI at the Z facility of Sandia National Laboratories, we developed a new experimental platform at the 1MA Zebra pulsed power accelerator of the University of Nevada, Reno based on using a gas jet produced by a supersonic nozzle. The gas jet is turned into a photoionized plasma driven by the x- ray flux from a wire-array z-pinch. Establishing this new experimental platform at Zebra was a major goal of this project. In addition, we have also dedicated effort to continue complementary experiments at the Z facility using the gas-cell photoionized plasma set up with support from the Fundamental Science Program at Z as well as to perform data processing and analysis, and theory and modeling simulations, including electron kinetics and radiation-hydrodynamics. Since we seek to test and establish what physics models are needed to describe photoionized plasma guided by experimental observation, these complementary experimental efforts were central to achieving the goals of this project.