Design of thick septa magnets based on 3D field calculation for the 3 GeV rapid cycling synchrotron of J-PARC

Watanabe, Masao  ; Irie, Yoshiro; Kamiya, Junichiro   ; Shimada, Taihei ; Takayanagi, Tomohiro   ; Fujimori, Hiroshi*; Igarashi, Susumu*; Kawakubo, Toshimichi*; Nakayama, Hisayoshi*

Thick septa are used in the injection and extraction section of the 3 GeV rapid cycling synchrotron of the J-PARC. We have been designing seven thick septum magnets, two for injection, two for beam dump and three for extraction, respectively. These septa require low-loss operations. For the mechanical stability they are operated by direct current. The yoke is made of the soft-iron block. We have been designing them by using the three-dimensional magnet static field calculation code, TOSCA. In this presentation, we discuss about magnetic field flatness in the gap and effects of the leakage fields in the synchrotron.