Particle-In-Cell Simulation on the Multipacting Process of a Novel High-Current Density Cathode

The configuration design of a novel high-current density cathode for producing a ring-like electron beam is briefly introduced. Due to the complicated physical process of this novel cathode, in this paper, only the temporal evolution of multipacting on this cathode surface is numerically simulated by using the particle-in-cell method. The simulation results indicate that the multipacting process could be successfully achieved on the surface of this cathode. In multipacting process, both the electron number and output current start rapid exponential increases in very short time and then tend to be saturation with slow decreases. The multipacting start point is not at the triple-junction (vacuum-metal-dielectric) region but has a distance to the region. The saturation region of multipacting will expand toward the outlet with the spreading speed on the order of 10
⁷
m/s, which agrees with the speed of the luminous front of the initial surface flashover measured by experiment, and the emission current density of the cathode could reach the level of kA/cm
²
. The region of multipacting electrons will first be lengthened and then will be shortened due to the region of deposited positive charges expanding to the outlet and the maximum value of deposited positive charges moving from the triple-junction region to the outlet side.