Repair Techniques of Superconducting Cavity for Improvement Cavity Performance at KEK-STF

Abstract

The repair techniques of superconducting cavity is important to obtain better yield of accelerating gradient of superconducting 1.3 GHz 9-cell cavities. The techniques for repair of the cavity are combination of the optical inspection, make a replica of defect, the local grinding and the result of temperature mapping in vertical test. The pit type defect (size: 0.7 mm x 0.5 mm, depth: about 115 um) was found at the quench location of MHI-08 cavity at 16 MV/m by optical inspection after 1st vertical test at June 2009. The location of defect is boundary between EBW seam and heat affected zone at 172 degree of 2-cell equator. If a cause of field limitation for MHI-08 is really this pit type defect, then the cavity can repair to remove the defect by mechanical grinding method. The defect was removed completely by the special grinding machine. After grinding, Electric polishing process and optical inspection were carried out to check the surface condition at grinding area. The 2nd vertical test of MHI-08 was carried out at October 2009. The accelerating field was improved from 16 MV/m to 27 MV/m. The result of repair of MHI-08 will be reported in this paper.