Investigation of Field-Emission-Driven Surface Flashover of Metal-Contaminated Dielectrics

Surface flashover in vacuum insulation is highly sensitive to metal contamination, which can locally distort electric fields and degrade dielectric performance, yet the underlying mechanisms remain poorly understood. This work investigates field-emission-driven flashover on metal-contaminated alumina ceramics through combined material characterization, electrical and optical diagnostics, supported by particle-in-cell simulations. Results show that nanoscale metal contaminations cause an exponential increase in surface leakage current from the nanoampere to the milliampere level. Acting as electrical floating potentials, these metal-contaminated regions strongly distort the local electric field, thereby enhancing field emission currents and ultimately reducing the breakdown threshold by up to 65.7%, from 14.0 kV to 4.8 kV. In addition, optical diagnostics reveal localized field-emission-induced luminescence emerging from metal-contaminated regions during the prebreakdown stage and intensifying with discharge development, demonstrating their direct involvement in seed electron generation and early flashover evolution. Simulation predictions are consistent with experimental observations, revealing strong coupling between metal and the cathode triple junction field, where the local field enhancement accelerates electron avalanche development and governs discharge progression. These findings uncover a coupled mechanism of field-emission-driven surface flashover on metal-contaminated dielectrics, emphasizing that metal contamination can fundamentally alter dielectric behavior and highlighting the critical importance of controlling surface conditions to ensure reliable vacuum insulation.