Speaker
Description
The single spoke resonator 1 (SSR1) is a superconducting RF cavity employed in the front section of high-energy linac of Rare isotope Accelerator complex for ON-line experiments (RAON). The SSR1 cavity features a balloon type geometry and is currently in the pre-production step to establish reliable fabrication and processing procedures prior to mass production. Four pre-production SSR1 cavities were fabricated and processed to evaluate and optimize the overall processing procedures with a focus on surface treatment and clean assembly. The optimized procedure includes rotational buffered chemical polishing (R-BCP) with an external cooling system, high-pressure rinsing (HPR) with ultrapure water quality control and rinsing conditions, and an established clean assembly procedure to minimize particle contaminations. To address bubble-induced surface streak patterns observed during stationary BCP, the R-BCP process with an external cooling system was implemented to improve etching uniformity and temperature control. In addition, ultrapure water quality was improved, and the rinsing procedure was refined to minimize particle ingress during the HPR process. And, clean assembly procedures reported at other accelerator facilities were reviewed and adapted to the RAON SSR1 configuration and assembly environment to minimize particle contamination. With these improvements, all cavities achieved Q0 values close to 1.0 × 10^10 at the target accelerating gradient of 7.9 MV/m. Furthermore, the X-ray dose measured during vertical tests was significantly reduced compared with that of cavities processed using the previous procedure. The reproducibility of the optimized procedure was verified through repeated processing and vertical tests. These results demonstrate the successful establishment of reliable and reproducible fabrication and processing procedures for the RAON SSR1 cavities, providing a technical basis for cryomodule development and future mass production for the high-energy superconducting linac.
This work was supported by the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT(RS-2022-00214790)