The design, manufacture and vertical testing of 648 MHz 6-cell elliptical cavity for CSNS-II

In order to increase the operating power of beam, China Spallation Neutron Source phase II (CSNS-II) will use two families of superconducting cavities (double-spoke cavity and elliptical cavity) to increase the energy of H − from 80 MeV in the phase I to 300 MeV. In January 2024, the project team successfully completed the prototype verification of the double-spoke superconducting cavity cryomodule. The maximum acceleration gradient of the double-spoke resonator (DSR) reached 15.2 MV/m, significantly surpassing the design target of 9 MV/m. The development of the elliptical cavity prototype began in March 2021. At present, the elliptical cavities have completed the prototype design, manufacturing, post-processing, and vertical testing, achieving a maximum gradient of 25.7 MV/m and a Q exceeding 1 × 10 10 , far surpassing the engineering requirement of 14 MV/m and the Q exceeds 5 × 10 9 . This paper details the design, fabrication, post-processing, and vertical testing of β = 0.62 elliptical cavities, covering challenges and solutions.