Activation in injection area of J-PARC 3-GeV rapid cycling synchrotron and its countermeasures

Yamamoto, Kazami   ; Yamakawa, Emi*; Takayanagi, Tomohiro   ; Miki, Nobuharu*; Kamiya, Junichiro   ; Saha, P. K.   ; Yoshimoto, Masahiro  ; Yanagibashi, Toru*; Horino, Koki*; Nakanoya, Takamitsu  ; Takeda, Osamu*

The existing beam power of the J-PARC Rapid Cycling Synchrotron is up to 500 kW, and higher radiation doses are concentrated in the injection area. These activations are caused by the interaction between the foil and the beam. To reduce dose exposure to workers near the injection point, we study a new design of the injection scheme. Experience has shown that eddy currents are generated in the metal flange near the magnet owing to the pulsed magnetic field, and the temperature exceeds 100 degrees C. The shield installed in the new injection system needs to have a layer structure, in which an insulator is inserted between iron shields to reduce the eddy current. From the results of the shielding calculation, even if 1 mm of polyethylene was inserted between two 9-mm-thick SUS 316 plates, which serve as shielding material, the shielding performance was reduced only about 5%, and we confirmed that it would function well.