Time-dependent modeling of photoionization wave propagation in nitrogen

Photoionization fronts are ubiquitous in astrophysics, but difficult to produce in a laboratory experiment. Recently, it was reported that photoionization fronts may be produced in nitrogen gas at pressure of ten atmospheres irradiated by a radiation source with temperature T_r ∼ 100 eV. We present two computational approaches to describe photoionization propagation in nitrogen gas induced by soft x-rays: 1. A time dependent in-line model that solves the ionization and the energy balance and the radiation transfer in a self-consistent way, and 2. A multi-group flux limited diffusion model based on two temperatures for the electrons and radiation, ionization and atomic data tables. Calculations were done for two spectrally different radiation sources, a laser irradiated gold foil and a blackbody Planckian source. It is shown that the atomic modeling and the spectral content of the source clearly affect the evolution of the nitrogen gas.