• C. Ohmori, E. Ezura, K. Hara, A. Koda, Y. Miyake, K. Nishiyama, K. Shimomura, M. Tada, A. Takagi, S. Takeshita, M. Yoshii
  KEK, Ibaraki
• K. Hasegawa, M. Nomura, A. Schnase, T. Shimada, H. Suzuki, F. Tamura, M. Yamamoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• M. Miyazaki
  GUAS, Kanagawa

J-PARC RCS accelerates a high intensity beam using 11 sets of Magnetic Alloy loaded cavities. It supplies the proton beam to the MLF (Material Life Science Facility) for the neutron and muon experiments. For very high resolution muon experiments, a short proton beam bunch of few ten ns is necessary. To reduce the bunch width to several ten ns, a bunch rotation scheme before extraction will be useful. For the bunch width of few ten ns, a much higher RF voltage is also required. Based on a new magnetic alloy core technology, a design of a new RF cavity to increase the maximum RF voltage by a factor of two will be described in this paper.