Report on first plasma processing trial for a FRIB quarter-wave resonator cryomodule

TL;DR

This paper reports the first plasma processing trial on FRIB quarter-wave resonator cryomodules, demonstrating significant reduction in field emission X-rays and highlighting plasma processing as a promising method for superconducting cavity maintenance.

Contribution

It presents the initial plasma processing application on FRIB QWR cryomodules, showing its effectiveness in improving cavity performance without removing cryomodules.

Findings

Significant reduction in field emission X-rays after plasma processing

Successful plasma processing using higher-order mode drive

First application of plasma processing on FRIB QWR cryomodules

Abstract

Plasma processing has been shown to help mitigate degradation of the performance of superconducting radio-frequency cavities, providing an alternative to removal of cryomodules from the accelerator for refurbishment. Studies of plasma processing for quarter-wave resonators (QWRs) and half-wave resonators (HWRs) are underway at the Facility for Rare Isotope Beams (FRIB), where a total of 324 such resonators are presently in operation. Plasma processing tests were done on several QWRs using the fundamental power coupler (FPC) to drive the plasma, with promising results. Driving the plasma with a higher-order mode allows for less mismatch at the FPC and higher plasma density. The first plasma processing trial for FRIB QWRs in a cryomodule was conducted in January 2024. Cold tests of the cryomodule showed a significant reduction in field emission X-rays after plasma processing.