Estimation time delay from field emission to secondary electron emission avalanche in vacuum surface flashover

Abstract

Vacuum surface flashover is the main factor limiting the development of pulsed power system. In this work, a quantitative dynamical model is built to investigate the vacuum surface flashover from field emission to secondary electron emission avalanche (SEEA). The results show that positive charges accumulating on the dielectric surface caused by field emission electrons play a dominant role when the normal electric field on the dielectric surface Edc is small. The growth of the number of positive surface charges exponentially decreases with the distance from the cathode triple junction (CTJ). With the increase in the density of positive surface charges, the growth of positive surface charges mainly depends on the secondary electrons cascade. As a result, the saturation state of Edc will first occur on the dielectric surface at a distance hundreds of micrometers from the CTJ. In addition, the effect of dielectric permittivity on positive surface charges is considered. The density of positive surface charges equals (1+εr) ε0Edc rather than 2ε0Edc. Particle-in-cell simulations are employed to verify the correctness of the theory model, and the agreement of comparisons is favorable. Furthermore, the space charge effect is discussed. When SEEA reaches saturation, electrons can significantly change the spatial distribution of the electric field.