650 MHz elliptical superconducting RF cavities for CiADS Project

Abstract 650 MHz multicell superconducting radio frequency (SRF) elliptical cavities are proposed for effective acceleration of proton beam in the Chinese initiative Accelerator Driven Subcritical System (CiADS). Two families of such cavities will be used in the driver superconducting linac to accelerate the H + beam from 175 MeV to 500 MeV, with the possibility to upgrade the energy to 1 GeV and higher. Detail designs of a six-cell β o p t = 0.62 elliptical cavity and a five-cell β o p t = 0.82 elliptical cavity will be presented in this paper, including the multi-parameter electromagnetic design and optimization, high order modes analyses, multipacting simulations, mechanical and engineering analyses. Sub-systems of the cavity such as the fundamental power coupler antenna tip design and mechanical design of cavity-helium vessel-tuner system will also be discussed in detail. Three single cell prototype cavities were fabricated and vertical tested to verify the electromagnetic properties, the fabrication and post-processing technologies. Four multi-cell prototype cavities are under manufacturing and expected to be ready in 2021.