The Mooncat experiment on the National Ignition Facility uses a laser-driven hohlraum to create a thermal radiation wave in a titanium-doped silica plasma. The titanium dopant enables absorption spectroscopy measurements to infer the temperature of the wave as it propagates. This measurement can be used to constrain multi-physics simulation codes to better understand when simulations do not match an experiment. In this paper, we present radiation-hydrodynamics simulations of the thermal radiation wave in the first full-platform shots of the Mooncat experiment. We examine the important parameters of the simulation, focusing on the radiation temperature source, the material model of the silica plasma as it pertains to radiation transport, and lateral leakage through a beryllium tube enclosing the silica. We compare different simulation modeling strategies to an analytic model of diffusive radiation transport and find that the simulation agrees with the analytic model when it is sufficiently simplified. These simulations show how radiation energy couples to matter to develop a shock wave in a radiative heat wave, an important topic in astrophysics and nuclear fusion plasmas.

Radiation flow through an inhomogeneous medium is critical in a wide range of physics and astronomy applications, from transport across cloud layers on the Earth to the propagation of supernova blast waves producing ultraviolet and X-ray emission. Radiation interacts with matter, driving hydrodynamic feedback that further alters the radiation characteristics (energy and angular distribution). This paper reviews the current state of the art in the modeling of inhomogeneous radiation transport, subgrid models developed to capture this often-unresolved physics, and the experiments designed to improve our understanding of these models. This paper focuses on simulations based on upcoming experiments designed to test this physics. We present a series of detailed simulations (both single-clump and multi-clump conditions) probing the dependence on the physical properties of the radiation front (e.g., radiation energy) and material characteristics (specific heat, opacity, clump densities). We find that, unless the radiation pressure is high, the clumps will heat and then expand, effectively cutting off the radiation flow. The expanding winds can also produce shocks that generates high-energy emission. We compare our detailed simulations with some of the current subgrid prescriptions, identifying some of the limitations of these current models.

Precise characterization of experimental radiation flow is required to validate the high energy density physics models, numerical methods, and codes that are used to simulate radiation-hydrodynamics phenomena such as thermal radiation transport in stochastic media. The Cassio code is used to simulate thermal radiation flow through inhomogeneous, stochastic-media-foam configurations containing optically thick clumps dispersed within an optically thin background aerogel. Cassio can model small inhomogeneous problems directly, but most problems require approximations to meet computer limitations on run-times and memory usage. Various examples of these approximations are methods that produce, in one calculation, an ensemble-averaged solution and associated standard deviation; reduced spatial dimensionality with approximate geometries; and full material homogenization with no geometric detail. Cassio simulations are used to design experiments at the OMEGA-60 Laser Facility that can measure the radiation flow using the spatially resolved COAX absorption spectroscopy diagnostic. The experimental platforms flow radiation through foam targets ranging from a background-only aerogel, to a single configuration of a specified stochastic medium, to a fully homogenized foam of the background and clump materials. Under constant total clump mass, larger clumps (here, larger than 10 μm diameter) will mix more slowly with the background such that the bulk radiation flow is faster than it would be in a fully homogenized material. The COAX platform can be used to infer temperature and density profiles in both the background material and clumps, simultaneously, and therefore to differentiate radiation flow in a range of stochastic and homogeneous media.

Sophisticated tools such as computer vision techniques in combination with 1D lineout type analyses have been used in automating the analysis of spectral data for high energy density (HED) plasmas. Standardized automation can solve the problems posed by the complexity of HED spectra and the quantity of data. We present a spectroscopic code written for automated and streamlined analysis of spatially resolved x-ray absorption data from the COAX platform on Omega-60. COAX uses radiographs and spectroscopic diagnostics to provide shock position and density information. We also obtain the more novel spectral-derived spatial profile of the supersonic radiation flow into a low-density foam. Considerable effort has been spent modernizing our previous spectroscopic analysis method, including the development of new tools characterized by a faster runtime and minimal user input to reduce bias and a testing suite for verifying the accuracy of the various functions within the code. The new code analyzes our spectroscopic images in 1-2 min, with added uncertainty and confidence.

Motivation: Recent theoretical modeling at LANL has demonstrated that the ignition criteria is a strong function of the temperature of the DT ice that surrounds the hot spot [Daughton et al. PoP 2023]. Alpha heating of the DT shell can raise the ignition threshold. Critical to modeling the alpha-particle deposition in the shell is understanding charged particle stopping in warm dense matter.

The XFOL campaign is continuing to study radiation flow in stochastic media. Purpose: Simultaneously measure the ionization state of the background and inclusions of a binary stochastic media using the COAX/OUTI diagnostic. Motivation: Radflow is stochastic media is of wide, growing interest and COAX is a new powerful diagnostic that can characterize the radflow physics and validate codes, models, and their underlying assumptions.

Both radiation flows and shocks have been extensively studied in the laboratory in the past few decades due to their critical roles in many astrophysical and high-energy density physics processes. In the Radishock experiment, a halfraum-powered radiation wave is driven into a low-density foam and interacts with an ablatively driven, counter-propagating shock. The interacting waves produce a spike in energy density with a temperature greater than the local temperature of the individual waves. As in the successful predecessor experiment, COAX, the primary diagnostic uses absorption spectroscopy at many locations down the cylindrical target, enabling a spatial temperature inference of the radiation wave and its interactions with the shock. Combined with a radiography diagnostic that is capable of imaging the shock and interaction features, we are able to study and inform model predictions of the interaction spike phenomenon. We describe the underlying physics behind the shock interactions with the radiation front and the implications of this experimental study for a broad range of astrophysical phenomena.

Spectral diagnostics provide a powerful probe of high energy-density physics experiments. By shining an x-ray source on a target, absorption features can be used to determine accurate temperature profiles of that target material. Many studies produce a single temperature/density measurement by fitting these observed spectra. This paper demonstrates how, by leveraging detailed simulations, we can not only measure the average temperature and density, but the full density and temperature profiles. To do so, we must conduct a careful analysis of the uncertainties in the diagnostic measurement. We discuss the characteristics and associated uncertainties of the spectral diagnostic used in the COAX, Radishock and OuTi experiments, ultimately demonstrating how these detailed studies increase the potential of this powerful probe.

The Radishock platform studies the interaction between a radiation wave and a counter-propagating shockwave within a Ti-laden silica aerogel foam using x-ray absorption spectroscopy and point-projection backlighter radiography from the COAX platform [1]. The radiation wave is produced by a laser-driven halfraum, and the shock wave via a directly-driven ablator. These experiments can provide insight into supernova shock breakout emission where the radiation flow breaking out of the star interacts with the circumstellar medium and the relative velocity between this breakout and the medium dictates the degree of heating in the shock. In our Radishock experiments, the radiation flow is not apparent in the radiographic diagnostic and can be directly observed only via the absorption spectroscopy diagnostic, which provides a measure of temperature and position. On the other hand, the shockwave launched from the ablator side of the target is observed in the radiographs, and we extract the full 2D shock front contour using computer vision techniques [2]. In the course of this analysis, we found features present in the late time interaction shots which were not present in the radiation wave only, shockwave only, and early time interaction shots. These features appear to be ablation driven off of the shock front by the interaction with the radiation wave, and it provides an indirect means of probing the radiation wave radiographically, and a direct means of probing the interaction itself.

The goal of the Xflows experimental campaign is to study the radiation flow on the National Ignition Facility (NIF) reproducing the sensitivity of the temperature (±8 eV, ±23 μm) and density (±11 mg/cc) measurements of the COAX platform [Johns et al., High Energy Density Phys. 39, 100939 (2021); Fryer et al., High Energy Density Phys. 35, 100738 (2020); and Coffing et al., Phys. Plasmas 29, 083302 (2022)]. This new platform will enable future astrophysical experiments involving supernova shock breakout, such as Radishock (Johns et al., Laboratory for Laser Energetics Annual Report 338, 2020) on OMEGA-60 [Boehly et al., Rev. Sci. Instrum. 66, 508 (1995)], and stochastic media (such as XFOL on OMEGA). Greater energy and larger physical scale on NIF [Moses et al., Eur. Phys. J. D 44, 215 (2007)] will enable a greater travel distance of radiation flow, higher density, and more manufacturable foams and enable exploration of a greater range of radiation behavior than achievable in the prior OMEGA experiments. This publication will describe the baseline configuration for the Xflows experimental campaign and the roadmap to achieve its primary objectives.

Magnetosonic waves are low-frequency, linearly polarized magnetohydrodynamic (MHD) waves commonly found in space, responsible for many well-known features, such as heating of the solar corona. In this work, we report observations of interesting wave signatures driven by injecting compact toroid (CT) plasmas into a static Helmholtz magnetic field at the Big Red Ball Facility at Wisconsin Plasma Physics Laboratory. By comparing the experimental results with the MHD theory, we identify that these waves are the fast magnetosonic modes propagating perpendicular to the background magnetic field. Additionally, we further investigate how the background field, preapplied poloidal magnetic flux in the CT injector, and the coarse grid placed in the chamber affect the characteristics of the waves. Since this experiment is part of an ongoing effort of creating a target plasma with tangled magnetic fields as a novel fusion fuel for magneto-inertial fusion (MIF), our current results could shed light on future possible paths of forming such a target for MIF.

Alfven waves are low-frequency, transverse magnetic tension waves that travel along magnetic field lines and can be excited in any electrically conducting fluid permeated by a magnetic field. They are commonly found in space, responsible for many well-known features, such as heating of the Sun's outer atmosphere, acceleration of solar wind, and aurora formed in high-latitude regions of the Earth. In this work, we present observations of standing Alfven waves excited by injecting compact toroid (CT) plasmas into a static Helmholtz magnetic field at the Big Red Ball (BRB) Facility at Wisconsin Plasma Physics Laboratory (WIPPL). The CT plasmas are injected in parallel with the magnetic field. The topology of the magnetic field in the standing Alfven waves is characterized using a 3-axis Bdot probe array.

The COAX platform has been used in numerous experiments to study radiation flow from a laser-driven halfraum down a low-density SiO2 foam laden with Ti, Sc, or V as spectroscopic dopants. These experiments, conducted first at OMEGA-60 and transitioning to NIF, utilize 1-D space-resolving absorption spectroscopy to characterize the radiation flow temperature to within +8eV and density within +11mg/cc. Parallel point-projection radiography measurements capture the development of the transonic and subsonic shock, and the combination strongly constrains radiation hydrodynamics simulations. This presentation will overview our body of work in this area and advertise applications to laboratory astrophysics, materials studies, and ICF.

Predicting and modeling the behavior of experiments with radiation waves propagating through low-density foams require a detailed quantification of the numerous uncertainties present. In regimes where a prominent radiative shock is produced, key dynamical features include the shock position, temperature, and curvature and the spatial distribution and temperature of the corresponding supersonic radiation wave. The COAX experimental platform is designed to constrain numerical models of such a radiative shock propagating through a low-density foam by employing radiography for spatial and shock information, Dante for characterizing the x-ray flux from the indirectly driven target, and a novel spectral diagnostic designed to probe the temperature profile of the wave. In this work, we model COAX with parameterized 2D simulations and a Hohlraum-laser modeling package to study uncertainties in diagnosing the experiment. The inferred temperature profile of the COAX radiation transport experiments has been shown to differ from simulations more than expected from drive uncertainties that have been constrained by simultaneous soft x-ray flux and radiography measurements.

radiation-hydrodynamics simulations, considering the axial uniformity of the implosion and feasibility of measuring the instability growth of pre-seeded single mode sinusoidal perturbations. We discuss in depth the design for a target to be directly driven at the OMEGA laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)]. We evaluate the design for axial implosion symmetry and visibility of instability growth using synthetic radiographs constructed from the simulations, as the instability growth on the inner cylinder is experimentally measured using x-ray radiography of the implosion. We find that the seeded perturbation growth on the inner cylinder should be visible in an experiment, even with axial implosion asymmetry and preheat. We compare our 2D simulations with linear theory predictions for perturbation growth and show that a cylinder with lower azimuthal mode number (mode-20) perturbations compares more favorably with linear theory, while a cylinder with higher azimuthal mode number (mode-40) perturbations at the same starting amplitude saturates and is over-predicted by linear theory.

In the Double Shell Inertial Confinement Fusion concept, characterizing the shape asymmetry of imploding metal shells is vital for understanding energy-efficient compression and radiative losses of the thermonuclear fuel. The Monte Carlo N-Particle MCNP® code forward models radiography of Double Shell capsule implosions using the Advanced Radiographic Capability at the National Ignition Facility. A procedure is developed for using MCNP to reconstruct density profiles from the radiograph image intensity. For a given Double Shell imploding target geometry, MCNP radiographs predict image contrast, which can help guide experimental design. In future work, the calculated MCNP synthetic radiographs will be compared with experimental radiographs to determine the radial and azimuthal density profiles of the Double Shell capsules.

In this paper, we report on a crystal based x-ray imaging system fielded at the OMEGA EP laser facility. This new system has a pointing accuracy of +/100 μm, a temporal resolution down to 100 ps (depending on backlighter characteristics), variable magnification, and a spatial resolution of 21.9 µm at the object plane at a magnification of 15×. The system is designed to use a crystal along the crystal plane that satisfies the Bragg condition for the x ray of interest. The thin crystal is then bent into a spherical geometry and attached to a glass backing substrate to hold it in the diagnostic, and the x rays are imaged onto a charge coupled device. We report on data acquired with the new Los Alamos National Laboratory supplied spherical quartz crystal to image the Mn He-α 6.15 keV line emission.