Susceptibility of multipactor discharges near a dielectric driven by a Gaussian-type transverse rf electric field

Abstract

Multipactor discharge near an rf window is a key limiting factor in high power microwave systems. In this work, we report special features of dielectric multipactor susceptibility under a Gaussian-type waveform as a function of the rf power density of the transverse rf electric field (P¯rf) and normal restoring field (Edc) via particle-in-cell (PIC) and multiple particle Monte Carlo (MC) simulations. The MC simulations show that, for a Gaussian waveform of a half peak width (Δτ), larger than Δτ/T=0.15 with T = 1 ns the rf repetition period, the susceptibility boundary is similar to that of the conventional sinusoidal waveform-driven multipactor, i.e., two inclined lines in the plane of (P¯rf,Edc). However, by decreasing Δτ, the susceptibility boundary converts to be a closed curve at Δτ/T=0.11 in the plane of (P¯rf,Edc) and further shrinks at Δτ/T=0.05. PIC simulations with a self-consistent surface and space charge effects also show a reduced Edc with increasing P¯rf when P¯rf exceeds a critical value, resulting in a closed curve in the plane of (P¯rf,Edc), and the maximum time-averaged Edc (multipactor strength) also decreases significantly with further decreasing Δτ in agreement with MC simulations. Accordingly, the fraction of the rf power density absorbed by the multipactor discharges also decreases nonlinearly with Δτ from the order of 10−2 to 10−3 (even 10−4), implying a significant improvement compared to the conventional sinusoidal waveform. The simulations also show that the multipactor susceptibility under a transverse Gaussian-type waveform for different frequencies follows the same scaling law in terms of the ratio of the electric field to the rf repetition rate.