Operation status of the charge exchange foil and replacement work of the foil transfer mechanism in the J-PARC 3GeV synchrotron

Nakanoya, Takamitsu ; Yoshimoto, Masahiro  ; Saha, P. K.   ; Takeda, Osamu*; Saeki, Riuji*; Muto, Masayoshi*; Miyo, Takuya*

The J-PARC 3 GeV Rapid Cycling Synchrotron (RCS) utilizes pure carbon foils produced in-house by JAEA as charge exchange foils. In November 2023, during beam commissioning just before the start of user operation, a malfunction occurred in a foil drive mechanism. The foil drive mechanism is responsible for replacing and inserting foils into the beamline. This malfunction prevented remote replacement of the foils. Therefore, when foil replacement was necessary, it was performed manually with visual confirmation near the mechanism. The foil drive mechanism was subsequently replaced and restored during the 2024 summer maintenance period. Despite the issue with the foil drive mechanism, the charge exchange foils demonstrated stability under beam irradiation, and there were no operational problems. Recent efforts have significantly enhanced the durability of the foils against beam irradiation through the implementation of two novel methods. One method involves selecting an appropriate diameter for the carbon rod used in charge exchange foil fabrication. The other method utilizes carbon nanotube (CNT) wire as a support material for the foils. While beam irradiation causes foil deformation, these methods show significantly reduced deformation compared to previous foils. This improvement raises the possibility of using foils for a longer operational lifespan. In this paper, we report on the foil drive mechanism malfunction, subsequent replacement work, and the performance of the charge exchange foils during user operation from 2023 to 2025.