High Q and high gradient performance of the first medium-temperature baking 1.3 GHz cryomodule

TL;DR

This paper reports the development and testing of the world's first medium-temperature baked 1.3 GHz cryomodule with eight superconducting RF cavities, achieving record-high Q0 and gradient performance for advanced light source applications.

Contribution

It introduces a novel medium-temperature baking process for 9-cell cavities in a cryomodule, resulting in unprecedented high Q0 and gradient performance, surpassing existing facilities.

Findings

Achieved highest average Q0 of 3.8E10 at 16 MV/m

Operated stably up to 191 MV total RF voltage

Cavities reached an average gradient of over 23 MV/m

Abstract

World's first 1.3 GHz cryomodule containing eight 9-cell superconducting radio-frequency (RF) cavities treated by medium-temperature furnace baking (mid-T bake) was developed, assembled and tested at IHEP for the Dalian Advanced Light Source (DALS) and CEPC R&D. The 9-cell cavities in the cryomodule achieved an unprecedented highest average Q0 of 3.8E10 at 16 MV/m and 3.6E10 at 21 MV/m in the horizontal test. The cryomodule can operate stably up to a total CW RF voltage greater than 191 MV, with an average cavity CW accelerating gradient of more than 23 MV/m. The results significantly exceed the specifications of CEPC, DALS and the other high repetition rate free electron laser facilities (LCLS-II, LCLS-II-HE, SHINE, S3FEL). There is evidence that the mid-T bake cavity may not require fast cool-down or long processing time in the cryomodule. This paper reviews the cryomodule performance and discusses some important issues in cryomodule assembly and testing.