Performance evaluation of charge exchange stripper foils for J-PARC 3GeV RCS

Yoshimoto, Masahiro  ; Nakanoya, Takamitsu  ; Yamazaki, Yoshio ; Saha, P. K.   ; Kinsho, Michikazu  ; Yamamoto, Shunya*; Okazaki, Hiroyuki*; Taguchi, Tomitsugu*; Yamada, Naoto*; Yamagata, Ryohei*

The multi-turn charge-exchange H beam injection scheme with stripper foils is one of the key techniques to achieve a MW-class high power proton beam. The J-PARC RCS adopts Hybrid type Boron-doped Carbon (HBC) stripper foil, which was developed in KEK to improve the lifetime. Indeed, the RCS user operation confirmed that HBC foil has the great advantage of a longer lifetime against high beam irradiation. To examine characteristics of the HBC foils, various beam studies were performed, such as the stripping efficiency measurement and long-term observation with an H beam in the J-PARC RCS, foil analysis using RBS, EDR and PIXE methods, and SEM and TEM observation after the ion beam irradiation in Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) on National Institutes for Quantum and Radiological Science and Technology (QST). Recently, the deposition apparatus for the HBC foils from the KEK Tsukuba-site was relocated to the JAEA Tokai-site, and we started fabrication of new HBC foil in 2017. (The new one fabricated in JAEA we call J-HBC foil.) And, we continue investigations in TIARA with the J-HBC foils. Furthermore, in-depth researches by changing the process parameters of the foil deposition are carried on. Now, we developed new types of foils which were made by arc discharge method by using a pure carbon rod for ether the anode electrode or the cathode electrode. As the results of the beam irradiation tests for the new types of HBC foils, it was suggested that the boron being carried in from the anode electrode plays an important part in the functioning of the stripper foil. The new knowledge will mark a milestone in the improvement of the stripper foil.