Suppression of multipacting growth in a superconducting spoke resonator by the use of higher order modes

Abstract

Abstract Multipacting is a vacuum discharge phenomenon that constrains the performance of accelerator structures and various microwave devices significantly. The different ways to mitigate multipacting discharge have been a central research goal in Accelerator Physics & Technologies for a prolonged period. In this work, both Monte-Carlo and particle-in-cell (PIC) simulations show that the multipactor avalanche can be mitigated, by the use of Higher Order Modes (HOMs). The intuition behind the approach of using HOMs to suppress multipacting has been explained first. Then, the multipacting suppression has been demonstrated in a simple 1-D metallic gap, when it is exposed to a second carrier frequency in addition to fundamental rf mode, with the help of a Monte-Carlo simulation code. Finally, a detailed PIC simulation has been carried out using CST Microwave studio, to investigate the effect of various HOMs on the multipactor growth in a superconducting spoke cavity. It is observed that a slight excitation of some particular modes can drastically diminish the multipactor growth. Simulation has been done first without any HOMs, to calculate the growth rate and also to spot the discharge location. Next, among various HOMs (more specifically, quadrupole modes), only those have been selected, whose magnetic field locations coincide with the multipacting prone zone of the cavity. In a simulation study, the presence of these preselected quadrupole modes has been found to exhibit a substantial suppression effect on the multipacting growth of the cavity.