Improved non-local radiation coupling for Mach2-TCRE

Summary form only given. (Mach2-TCRE is a two-dimensional (R-Z) radiation MHD Z-pinch simulation code with non-LTE population kinetics and radiation transport using ray tracing. The tabular collisional radiative equilibrium (CRE) based equation-of -state (EOS) model used in this code requires three table inputs: ion density, specific internal energy, and the effective escape probability in a strong radiating line, one from each ionization state.¹ In the past, to simplify the 2D calculation of escape probabilities we employed the “on-the-spot” approximation² (OTS), i.e., if a photon is absorbed anywhere in the plasma it is assumed to be absorbed in the emitting zone. While this approximation, has been demonstrated to be reasonable for treating bulk K-shell emission in Z-pinch simulations, it does not directly account for the zone-to-zone coupling of radiation that is required to accurately calculate the escape probabilities. Here we compare 1D and 2D EOS calculations using the OTS approximation to infer escape probabilities versus a new fast ray-trace scheme³ that allows us to directly treat the zone-to-zone coupling required for an accurate escape probability calculation.