An important breakthrough has been made on IHEP's high Q 1.3 GHz 9-cell cavities. Two fine grain 1.3 GHz 9-cell cavities reached a high quality factor (Q) of 3.7E10 and 4.0E10 at 16 MV/m with a maximum gradient of 22.7 MV/m and 26.5 MV/m, respectively, in the 2 K vertical test. There is no field emission induced radiation during the vertical test. 

These are the world's first high Q 1.3 GHz 9-cell cavities treated with the medium-temperature (mid-T) furnace bake method. Both the two cavities' Q values and the maximum gradients exceed SHINE (Shanghai HIgh-repetition-rate XFEL aNd Extreme light facility) and LCLS-II & LCLS-II-HE (Linac Coherent Light Source II and its High Energy upgrade) specifications. In addition, one of the two cavities reached 3.6E10 at 24 MV/m, which exceeds the CEPC (Circular Electron Positron Collider) cavity vertical test specification.

Based on FNAL and KEK's experience on mid-T single cell cavities and IHEP's recent R&D on high gradient and high Q cavities, IHEP investigated and further improved the mid-T furnace bake method with single cell cavities and recently made the first successful trial on 9-cell cavities. The cavities are fabricated by the IHEP Workshop (Beijing HE-Racing Technology Co.).

1.3 GHz 9-cell cavities are and will be widely used in many SRF accelerators all over the world, including Euro-XFEL, LCLS-II, SHINE and other SRF FELs in China, ILC and CEPC.