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

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 ( E dc) 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 ( Δ τ), larger than Δ τ / 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 , E dc). However, by decreasing Δ τ, the susceptibility boundary converts to be a closed curve at Δ τ / T = 0.11 in the plane of ( P ¯ rf , E dc) and further shrinks at Δ τ / T = 0.05. PIC simulations with a self-consistent surface and space charge effects also show a reduced E dc with increasing P ¯ rf when P ¯ rf exceeds a critical value, resulting in a closed curve in the plane of ( P ¯ rf , E dc), and the maximum time-averaged E dc (multipactor strength) also decreases significantly with further decreasing Δ τ in agreement with MC simulations. Accordingly, the fraction of the rf power density absorbed by the multipactor discharges also decreases nonlinearly with Δ τ 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.