The Multipactor Simulation and Thresholds Analysis for an Impedance Transformer by an Improved 3-D PIC Method Combined With Particle Merging

In this study, a secondary electron emission (SEE) module is updated to Alioth, a 3-D electromagnetic (EM) particle-in-cell (PIC) software for simulating the multipactor. To solve the problems of low computational efficiency and overburden caused by the considerable number of secondary electrons, a particle merging scheme based on the Russian roulette is introduced. The multipactor process of an impedance transformer is investigated from the generation of seed electrons to the saturation through the 3-D PIC method combined with the particle merging scheme. The time evolution characteristics of the space charge during the multipactor are calculated to analyze the multipactor threshold of the impedance transformer. Based on the evolution of the electrons and space charge, the changes of
${S}_{{11}}$
, and the generation of the third harmonic, the multipactor threshold is researched thoroughly. The error of the threshold results between the simulation and experiment is 0.296 dB, which shows the good agreement of Alioth with the measures.