Multipacting

TL;DR

This paper analyzes the phenomenon of multipacting in RF structures, providing analytical solutions, rules of thumb for critical field levels, and validating these with computer simulations to better understand and predict MP discharges.

Contribution

It offers an analytical framework for understanding multipacting in axial-symmetric cavities and introduces practical rules for estimating critical RF field levels to prevent MP.

Findings

Analytical solutions for MP conditions in simple cavities

Development of 'poor man's rules' for critical field estimation

Validation of rules through computer simulations

Abstract

Multipacting (MP) is a resonant electron discharge, often plaguing radiofrequency structures, produced by the synchronization of emitted electrons with the RF fields and by the electron multiplication at the impact point with the surface of the structure. The current of re-emitted electrons grows via true secondary re-emission when the secondary yield for the primary electron impact energy is greater than one. A simple example (MP in short-gap accelerating axial-symmetric cavities) allows an analytical solution of the equation of motion, giving both the synchronization (kinematics) and multiplication (impact energy) conditions as a function of the gap voltage (or accelerating field). Starting from this example a thorough discussion of MP discharges in axial-symmetric accelerating structures will be given and some poor man's rules are given to estimate the critical cavity field levels to meet the kinematic condition for resonance. The results of these poor man's rules are compared with computer simulations of MP discharges obtained by a statistical analysis of the re-emission yield for impinging electrons versus RF field level in the accelerating structure.