NSFC, Beijing
PKU/IHIP, Beijing
Considerable progress has been made in China with TESLA technology since SRF 2007. As a mid-term goal, Peking University is striving for constructing an ERL test facility to provide coherent radiation. A cryomodule of an upgraded DC-SRF injector with a 3.5 cell cavity of large grain niobium was designed and constructed for this purpose. The field gradient of the injector cavity in the vertical test at J-Lab is reported as 23.5MV/m. A cryomodule consisting of a China made 9-cell TESLA type cavity is also presented. As the helium liquefier system produced by the Linde Company is being commissioned, it is expected that the PKU test facility will be able to provide 15-20 MeV high quality e-beam at an operating temperature of 2K early next year. Apart from PKU, IHEP started a program to build a short cryomodule consisting of a 1.3GHz 9-cell cavity and related components to serve as a horizontal test stand under the frame of ILC collaboration. The R&D of a 500MHz single-cell Nb cavity module as a spare SRF component of the colliding ring is also in progress. In order to manipulate the beam bunch length on the SSRF ring, 1.5 GHz single cell SRF cavities are being developed at SAIP.
PKU/IHIP, Beijing
DC-SC photocathode injector was upgraded for Peking University Free Electron Laser (PKU-FEL) facility. A 3.5-cell superconducting cavity is the key component of the DC-SC photoinjector. Design and simulation of the 3.5-cell cavity was finished. Two 3.5-cell SRF cavities was fabricated at Peking University. One is made of large grain niobium and the other is made of fine grain niobium. All the material are from Ningxia OTIC. After BCP treatment and 1250 C post purification by Peking University, the 3.5-cell LG cavity was sent to Jlab for test. Due to the special structure , the cavity was treated with BCP, 800 C degassing and HPR at Jlab. The Eacc of the cavity reached 23 MV/m with Q=1.2·1010 at highest gradient. The 3.5-cell LG Nb cavity was installed to the new DC-SC photoinjector and will be tested with the cryomodule for the next step.
PKU/IHIP, Beijing
As a part of research on the fabrication of 9-cell niobium cavity, a polishing technology based on Buffered Electro-polishing (BEP) was carried on by Peking University. Compared with traditional electro-polishing, it has distinct advantages especially in the polishing rate and polishing effect. Through improvement, the maximum mass removal rate could reach 4.66μm/min in our experiments. It was over 10 times higher than the polishing rate of traditional EP. Meanwhile, the surface RMS roughness was about 20nm. At present, we are under the research to apply this new technology to a demountable cavity and have got preliminary results.