Computational Modeling of High Pressure Gas Breakdown and Streamer Formation in External Electric Fields

Summary form only given. The development of new computational models of gas breakdown for use in particle-in-cell (PIC) codes is described. These modeling efforts include fundamental processes associated with the breakdown of high pressure gases and represent key first steps in comprehensive studies of the physics of high-pressure gas switches. Two computational algorithms are described; a Monte Carlo type collision (MCC) model whereby PIC macro-particles undergo random elastic and inelastic interactions, and a semi-fluid scattering model. A newly implemented attachment algorithm, important for electronegative gases such as SF₆, has been developed. The details of the cross-section compilations for H₂ and SF₆ for use in the MCC algorithm are summarized along with the modeling assumptions that are made to make this model computationally tractable. The results of detailed swarm calculations using these cross-sections are presented along with comparisons to experimental data. The existing implicit semi-fluid collision model in the PIC code LSP is used to carry out 2D (r,z) streamer simulations. These simulations track the formation and evolution of a streamer from a small seed electron population in different applied electric fields. The results of H₂ and SF₆ streamer simulations are presented, including comparisons between the semi-fluid and MCC model for streamer formation and evolution in H₂.