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Title: Laboratory Photoionization Fronts in Nitrogen Gas: A Numerical Feasibility and Parameter Study

Photoionization fronts play a dominant role in many astrophysical situations but remain difficult to achieve in a laboratory experiment. We present the results from a computational parameter study evaluating the feasibility of the photoionization experiment presented in the design paper by Drake et al. in which a photoionization front is generated in a nitrogen medium. The nitrogen gas density and the Planckian radiation temperature of the X-ray source define each simulation. Simulations modeled experiments in which the X-ray flux is generated by a laser-heated gold foil, suitable for experiments using many kJ of laser energy, and experiments in which the flux is generated by a "z-pinch" device, which implodes a cylindrical shell of conducting wires. The models are run using crash, our block-adaptive-mesh code for multimaterial radiation hydrodynamics. The radiative transfer model uses multigroup, flux-limited diffusion with 30 radiation groups. In addition, electron heat conduction is modeled using a single-group, flux-limited diffusion. In the theory, a photoionization front can exist only when the ratios of the electron recombination rate to the photoionization rate and the electron-impact ionization rate to the recombination rate lie in certain ranges. These ratios are computed for several ionization states of nitrogen. Photoionization fronts are foundmore » to exist for laser-driven models with moderate nitrogen densities (~10 21 cm –3) and radiation temperatures above 90 eV. For "z-pinch"-driven models, lower nitrogen densities are preferred (<10 21 cm –3). Here, we conclude that the proposed experiments are likely to generate photoionization fronts.« less
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  1. Univ. of Michigan, Ann Arbor, MI (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 858; Journal Issue: 1; Journal ID: ISSN 1538-4357
Institute of Physics (IOP)
Research Org:
Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Programs (DP) (NA-10)
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; atomic processes; dark ages; reionization; first stars; galaxies: structure; Astrophysics - Astrophysics of Galaxies; Astrophysics - Solar and Stellar Astrophysics
OSTI Identifier: