Monte Carlo versus bulk conductivity modeling of RF breakdown of helium

A Monte Carlo collision model and a bulk conductivity model have been implemented in the finite-difference time-domain code Lsp to allow simulation of weakly-ionized plasmas. The conductivity model uses only mesh quantities derived from moments of the electron distribution function, while the Monte Carlo model uses particles to provide a detailed representation of the electric distribution function. The models are compared in simulations of Helium gas breakdown in an applied radio frequency radio frequency (RF) electric field. The conductivity model assumes that the free electron velocity distribution equilibrates instantly with the applied field, and transport coefficients for the model are obtained from steady-state solutions of the Boltzmann equation. For Helium near standard temperature and pressure (STP) and a 1-GHz applied electric field, the conductivity model is found to agree well with the Monte Carlo model and is orders of magnitude faster. The Monte Carlo model, which treats scattering and ionization of particles in a detailed way, captures transient effects associated with finite electron heating and cooling times which are absent from the conductivity model