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.
JLAB, Newport News, Virginia
CEA, Gif-sur-Yvette
PKU/IHIP, Beijing
ORNL, Oak Ridge, Tennessee
BNL, Upton, Long Island, New York
Buffered electropolishing (BEP) is a Nb surface treatment technique developed at Jefferson Lab1. Experimental results obtained from flat Nb samples show2-4 that BEP can produce a surface finish much smoother than that produced by the conventional electropolishing (EP), while Nb removal rate can be as high as 4.67 μm/min. This new technique has been applied to the treatments of Nb SRF single cell cavity employing a vertical polishing system5 constructed at JLab as well as a horizontal polishing system at CEA Saclay. Preliminary results show that the accelerating gradient can reach 32 MV/m for a large grain cavity and 26.7 MV/m for a regular grain cavity. In this presentation, the latest progresses from the international collaboration between Peking University, CEA Saclay, and JLab on BEP will be summarized.
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.