The design of a photoionization front experiment using the Z-Machine as a driving source and estimated measurements

Abstract

Radiation-driven heat fronts are present in the early universe during reionization, the circumstellar medium of supernovae, and in high-energy-density physics experiments. Dedicated experiments to observe and diagnose the behavior of these types of heat fronts can improve our understanding of these phenomena. A simulation study of photoionization fronts using the HELIOS-CR radiation hydrodynamics code provides an experimental design for the Z-Machine at Sandia National Laboratory using a measurement-calibrated input radiation flux to drive the photoionization front. The simulations use detailed atomic physics and non-diffusive radiation transport in 1D to determine an optimal gas pressure of 0.75 atm for an experiment in N gas as well as the effects of increasing the thickness of the window that seals the gas cell. Post-processing of these simulations demonstrates that ratios of atomic rate coefficients place the heat front in a physics regime where photoionization dominates the energy deposition. To see the sensitivity of the simulations to changes in the model and spatial grid, this analysis performed resolution, atomic model detail, and radiation transport angular grid studies showing less than 10% deviation from the nominal model for increased complexity, when possible. An effort to emulate 3D geometric effects on the radiation flux using an artificial attenuation scheme has shown that, even for conservative estimates of the flux, simulations still produce a photoionization front. Estimations of a streaked, visible spectroscopy measurement using SPECT3D showed that line emission measurements are present early in time and that later in time thermal emission should become dominant.

A time-resolved imaging system for the diagnosis of x-ray self-emission in high energy density physics experiments

“…Examples of experiments with a quasi-one-dimensional geometry include the work on photoionization fronts which currently form part of the work done by the Z Astrophysical Plasma Properties (ZAPP) collaboration. 7 The design we present was used to diagnose x-ray self-emission in reconnection experiments performed on the MAGPIE generator at the Imperial College. 8 A diagnostic based on the design described here is also being developed to diagnose plasma dynamics in magnetic reconnection experiments performed on the Z-Machine at Sandia National Laboratories.…”

A Time-Resolved Imaging System for the Diagnosis of X-ray Self-Emission in High Energy Density Physics Experiments

“…Examples of experiments which are extended in one dimension include gas-puff or wirearray Z-Pinch implosions. Examples of experiments with a quasi one dimensional geometry include the work on photoionisation fronts which currently form part of the work done by the Z Astrophysical Plasma Properties (ZAPP) collaboration [7].…”