Fabrication of the prototype spoke cavity for the JAEA-ADS linac

Tamura, Jun  ; Kondo, Yasuhiro   ; Yee-Rendon, B. ; Meigo, Shinichiro   ; Maekawa, Fujio  ; Kako, Eiji*; Umemori, Kensei*; Sakai, Hiroshi*; Domae, Takeshi*

Japan Atomic Energy Agency (JAEA) has been proposing an accelerator-driven nuclear transmutation system (ADS) as a future nuclear system to efficiently reduce high-level radioactive waste generated in nuclear power plants. As the first step toward the full-scale CW proton linac for the JAEA-ADS, we are currently prototyping a low-beta (around 0.2) single-spoke cavity. Since there is no experience in manufacturing superconducting spoke cavities in Japan, prototyping and performance evaluation of the cavity are essential to ensure the feasibility of the JAEA-ADS. The actual cavity fabrication started in 2020, and the cavity assembly by electron beam welding was finally completed in fiscal year 2024. In this assembly, the target resonance frequency of 324 MHz was achieved by trimming the ends of the cavity parts several times before the final welding. In the final welding, smooth weld beads were obtained by combining circular-correction and end-thinning for the cavity parts to be welded. The fabrication of the prototype spoke cavity is presented.