Multipacting Processing in Cryomodules For LCLS-II And LCLS-II-HE

TL;DR

This paper investigates multipacting phenomena in superconducting RF cavities used in LCLS-II projects, demonstrating processing methods to mitigate MP effects and improve accelerator performance.

Contribution

It presents new multipacting processing techniques in cryomodules, validated through testing in LCLS-II and LCLS-II-HE accelerators.

Findings

MP processing methods effectively conditioned cryomodules

Processing success maintained over mid-term operation

Cryomodule testing confirms mitigation of MP effects

Abstract

Multipacting (MP) is a phenomenon which can affect stability in particle accelerators and limit performance in superconducting radio frequency cavities. In the TESLA shaped, 1.3 GHz, 9-cell cavities used in the LCLS-II (L2) and LCLS-II-HE (HE) projects, the MP-band (~17-24 MV/m) lies within the required accelerating gradients. For HE, the operating gradient of 20.8 MV/m lies well within the MP-band and cryomodule testing has confirmed that this is an issue. As such, MP processing for the HE cryomodule test program will be discussed. Early results on MP processing in cryomodules installed in the L2 linac will also be presented, demonstrating that the methods used in cryomodule acceptance testing are also successful at conditioning MP in the accelerator and that this processing is preserved in the mid-term.