Dependence of charge-exchange efficiency on cooling water temperature of a beam transport line

Yamamoto, Kazami   ; Hatakeyama, Shuichiro; Saha, P. K.   ; Moriya, Katsuhiro  ; Okabe, Kota  ; Yoshimoto, Masahiro  ; Nakanoya, Takamitsu  ; Fujirai, Kosuke; Yamazaki, Yoshio ; Suganuma, Kazuaki 

The 3 GeV Rapid Cycling Synchrotron at the Japan Proton Accelerator Research Complex supplies a high-intensity proton beam for neutron experiments. Various parameters are monitored to achieve a stable operation, and it was found that the oscillations of the charge-exchange efficiency and cooling water temperature were synchronized. We evaluated the orbit fluctuations at the injection point using a beam current of the injection dump, which is proportional to the number of particles that miss the foil and fail in the charge exchange, and profile of the injection beam. The total width of the fluctuations was approximately 0.072 mm. This value is negligible from the user operation viewpoint as our existing beam position monitors cannot detect such a small signal deviation. This displacement corresponds to a 1.6310 variation in the dipole magnetic field. Conversely, the magnetic field variation in the L3BT dipole magnet, which was estimated by the temperature change directly, is 4.0810. This result suggested that the change in the cooling water temperature is one of the major causes of the efficiency fluctuation.