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CLASSE NEWS | 29 Nov 2017

World Record Q in a 500 MHz SRF cavity by Nitrogen Doping

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B-Cell cavity undergoes vertical testing

Cornell’s SRF group is collaborating with Brookhaven National Laboratory (BNL) on one 500MHz CESR type SRF “B-cell” cavity (BNL B-cell) for the National Synchrotron Light Source II. Cornell is responsible for RF surface preparation, vertical testing, and short cavity string assembly.

As a state-of-the-art surface preparation protocol, Cornell selected “Nitrogen doping” for BNL B-cell. N-doping has been well demonstrated and established to push the cavity quality factor (Q0) higher in 1.3GHz SRF cavities at many laboratories. Cornell calculated that N-doping could also be beneficial on a 500MHz SRF cavity and with the potential to increase its Q0 by a factor of two compared with the traditional chemical polishing based surface preparation protocol.

The N-doped BNL B-cell cavity, the first N-doped 500MHz cavity in the world, was tested in the vertical test pit at Newman Lab. The cavity achieved a Q0 of 1.4x109 at an accelerating field gradient of 12MV/m when operated at 4.2K, which is a world record Q0 for a B-cell cavity at that gradient. The performance limitation was available RF power during the vertical test; the cavity showed no quench limit during the test. This development will impact future storage ring facilities driven by low-frequency SRF cavities by significantly reducing cryogenic loads. Further high Q R&D on B-cell cavities will continue at Cornell.

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