FlashSim: A novel particle-in-cell numerical model for vacuum surface flashover simulation based on finite element method

Abstract

In vacuum-dielectric insulation systems, surface flashover is commonly considered as an interfacial breakdown induced by high electric field, posing a significant threat to the stable and safe operation of numerous vacuum equipment. To clarify its development mechanism and propose relevant suppression strategies, a novel Particle-in-Cell (PIC) vacuum surface flashover simulation model, FlashSim, based on finite element method (FEM), is introduced. The model computes the real-time electric field at cathode triple junction (CTJ) where seed electrons are generated. Electron collisions with the dielectric surface, including elastic backscattering, inelastic backscattering, and true secondary electron emission, are considered. Firstly, the flashover simulation with flat dielectric surface and parallel-plate electrodes shows that electric field at CTJ is enhanced due to surface charge accumulation, leading to an increase in field electron emission (FEE). Low-energy (<53 eV) electrons concentrate near the dielectric surface due to positive charging in the dielectric layer, while high-energy (53eV-1.9 keV) electrons can escape into higher vertical positions. Furthermore, the model employs adaptive mesh, enabling high simulation accuracy without compromising the computational time. Notably, the adopted FEM mesh generator can handle complex boundary geometries, which is validated by simulations with surface grooving for promoting the flashover capability. The performance of grooves is evaluated through electron distribution, anode current density, average surface charge density and electron flux, demonstrating higher flashover strength. The proposed FlashSim simulation model is expected to assist in further revealing the flashover mechanism and developing novel strategies for flashover suppression, and will be further upgraded to include outgassing and plasma discharge.