Importance of number of gap crossings on secondary emission in the simulation of two-sided multipactor

Abstract

Superconducting RF (SRF) cavities have been used in modern accelerators. Among the factors that limit the maximum RF voltage of SRF cavities and the maximum RF power delivered by them, the major limitation comes from multipacting (MP) in the cavity and waveguide. The vacuum waveguide of CESR (Cornell Electron-positron Storage Ring) RF system is the case where parallel plates can be used for simulating MP inside of the waveguide. To investigate, the importance of the number of gap crossings on secondary emission in two-sided multipactor, Monte Carlo (MC) method within a parallel plate model is employed, using a wide range of parameters. It is found that in order to arrive at a correct estimate for the threshold value of secondary yield (above which secondary electron multipaction occurs), one needs to consider a larger number of gap crossings than is usually done in simulations. Numerical simulation demonstrates an increase in the number of gap crossings may raise the electron population or the number of secondary emission yield averaged over the number of electrons impacts (MY), to significant levels producing MP phenomenon, changing the assessment of the threshold value of the secondary yield.