Uncut core loaded cavity with parallel inductor to reach Q=2 for J-PARC RCS

Schnase, A.; Hasegawa, Katsushi; Nomura, Masahiro  ; Tamura, Fumihiko   ; Yamamoto, Masanobu   ; Anami, Shozo*; Ezura, Eiji*; Hara, Keigo*; Hashimoto, Yoshinori*; Omori, Chihiro*; Takagi, Akira*; Toda, Makoto*; Yoshii, Masahito*

The optimum quality factor of the acceleration cavities for the J-PARC Rapid Cycling Synchrotron is Q=2. The first approach used cut-cores, where the distance between core halves in the cavity tank defines the quality factor while keeping the shunt impedance. Problems in core manufacturing made it unlikely that such cavities can operate for long time. The next step was a Q=2 hybrid structure; 4 of the 6 cavity tanks are filled with uncut cores at Q=0.6 and only 2 tanks are loaded with cut cores at wider distance (Q=4), which is easier to manage. Issues with the cut-core manufacturing remained, so RCS day-1 operation will start with uncut core cavities. However, Q=0.6 limits the maximum beam power. We present an idea, based on the hybrid cavity to add a parallel high quality circuit of inductor and capacitor to change the resonant frequency from 1 to 1.7 MHz and the total Q-value from 0.6 to 2, thus enabling almost full beam power operation of RCS with uncut cores loaded cavities.