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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
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ; ORCiD logo [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
Publication Date:
Grant/Contract Number:
NA0002956
Type:
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
Publisher:
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
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; atomic processes; dark ages; reionization; first stars; galaxies: structure; Astrophysics - Astrophysics of Galaxies; Astrophysics - Solar and Stellar Astrophysics
OSTI Identifier:
1461200

Gray, William J., Keiter, P. A., Lefevre, H., Patterson, C. R., Davis, J. S., van Der Holst, B., Powell, K. G., and Drake, R. P.. Laboratory Photoionization Fronts in Nitrogen Gas: A Numerical Feasibility and Parameter Study. United States: N. p., Web. doi:10.3847/1538-4357/aabc0f.
Gray, William J., Keiter, P. A., Lefevre, H., Patterson, C. R., Davis, J. S., van Der Holst, B., Powell, K. G., & Drake, R. P.. Laboratory Photoionization Fronts in Nitrogen Gas: A Numerical Feasibility and Parameter Study. United States. doi:10.3847/1538-4357/aabc0f.
Gray, William J., Keiter, P. A., Lefevre, H., Patterson, C. R., Davis, J. S., van Der Holst, B., Powell, K. G., and Drake, R. P.. 2018. "Laboratory Photoionization Fronts in Nitrogen Gas: A Numerical Feasibility and Parameter Study". United States. doi:10.3847/1538-4357/aabc0f.
@article{osti_1461200,
title = {Laboratory Photoionization Fronts in Nitrogen Gas: A Numerical Feasibility and Parameter Study},
author = {Gray, William J. and Keiter, P. A. and Lefevre, H. and Patterson, C. R. and Davis, J. S. and van Der Holst, B. and Powell, K. G. and Drake, R. P.},
abstractNote = {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 found to exist for laser-driven models with moderate nitrogen densities (~1021 cm–3) and radiation temperatures above 90 eV. For "z-pinch"-driven models, lower nitrogen densities are preferred (<1021 cm–3). Here, we conclude that the proposed experiments are likely to generate photoionization fronts.},
doi = {10.3847/1538-4357/aabc0f},
journal = {The Astrophysical Journal (Online)},
number = 1,
volume = 858,
place = {United States},
year = {2018},
month = {4}
}