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.
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