Incorporating radiation transport into particle-based plasma simulations

In an effort to expand modern Particle-in-Cell (PIC) plasma simulations, a method for including radiation transport is examined. Tracking the dynamics of radiation transport in plasma simulations is inherently difficult and most models use either a semi-empirical or a propagator function approach. Here, discrete photons are emitted from excited state species with a state-dependent wavelength. This self-produced emission from the plasma is broadened according to natural and Doppler line widths resulting in a Voigt profile and emitted isotropically. By directly tracking the velocities of the excited species that emit radiation, the Doppler shift is easily found and the expensive convolution calculation for the Voigt profile is avoided. Absorption cross sections of radiation by the background neutral gas cross sections for ground-state are determined as a function of the emission profile. As such, discrete photon particles also have the advantage of being easily coupled to an existing collision routine such as Direct Simulation Monte Carlo (DSMC) or Monte Carlo Collision (MCC). Simulations of helium and air discharges demonstrate the effectiveness of this method for determining non-equilibrium emission spectra and incorporating energy-dependent photo-processes (e.g. photoemission, photo-ionization).