Influence of Global Numerical Parameters on PIC-MCC Simulations of Postarc Sheath Dynamics in Vacuum Circuit Breakers

Abstract

The particle-in-cell with Monte Carlo collision (PIC-MCC) method has been widely used to investigate the plasma dynamics after arc extinction in vacuum circuit breakers (VCBs), while its accuracy and efficiency strongly depend on the selection of global numerical parameters. In this work, a systematic parametric study is performed using a simplified 2-D PIC-MCC model to evaluate the influence of key parameters, including the number of super-particles per cell, cell length, time step, dump period, and the number of cells in the radial direction. The results show that increasing the number of super-particles per cell suppresses statistical fluctuations, while the postarc current (PAC) and sheath results converge when the number reaches approximately 40–50 per cell. Simulations with a cell length of $5\times 10^{-6}$ m and a time step of $2\times 10^{-12}$ s produce results nearly identical to those obtained with finer discretization, whereas larger values lead to noticeable deviations in sheath evolution. The dump period does not alter the underlying PIC-MCC solution but affects the temporal sampling and finite-difference resolution used in PAC extraction. Increasing the number of radial cells from 2 to 4 produces no systematic change in the PAC duration or sheath filling time but significantly increases computational cost. Based on these results, optimized parameter selections are recommended to achieve a balance between numerical accuracy and efficiency.