Development of HOM absorbers for CW superconducting cavities in energy recovery linac

Higher Order Modes (HOM) absorbers for superconducting cavities in energy recovery linac (ERL) have been developing at TOSHIBA in collaboration with High Energy Accelerator Research Organization (KEK) since 2015. A prototype HOM absorber for 1.3 GHz 9-cell superconducting cavity was fabricated in 2017. An aluminum nitride based lossy dielectrics (AlN) cylinder was brazed in a copper cylinder which has lattice-like slots on the inner surface. RF performance measurements of this prototype HOM absorber at room temperature and low temperature were carried out at KEK. As the results, it was found that some HOMs were absorbed by the prototype HOM absorber. However, many cracks occurred in the AlN cylinder before these measurements. R&D of brazing between AlN cylinder and copper has started and a new prototype HOM absorber was fabricated based on the R&D results. The heat removal test of the new prototype HOM absorber was carried out. RF measurement results of the previous prototype HOM absorber and fabrication process and the heat removal test results of the new prototype HOM absorber will be presented in this paper. (author)