Design and construction of septum magnets at 3-GeV RCS in J-PARC

Yoshimoto, Masahiro  ; Ueno, Tomoaki; Togashi, Tomohito; Takeda, Osamu; Kanazawa, Kenichiro; Watanabe, Masao  ; Yamazaki, Yoshio ; Kamiya, Junichiro   ; Takayanagi, Tomohiro   ; Kuramochi, Masaya; Kinsho, Michikazu  ; Irie, Yoshiro; Fujimori, Hiroshi*; Igarashi, Susumu*; Nakayama, Hisayoshi*

There are seven septum magnets for the beam injection and extraction at the RCS in J-PARC. In design of the septum magnets, the most important is that the magnetic leakage field outside the septum will disappear, but it is difficult in fact. In order to reduce the leakage field from the septum magnets at the beam orbit in the ring, the silicon steel sheets are set at the outside of the septum magnets as the magnetic shields. However sufficient spaces to set the thick magnetic shields are not securable at the divergent duct areas. Therefore the vacuum chambers are made by the magnetic stainless steel and the leakage fields in the chambers can be reduced. As results of the 3D field calculations by TOSCA, the magnetic leakage field can be suppressed to a few Gauss or less.