  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.
