Development of MA core for J-PARC Ring RF Cavity

Nomura, Masahiro  ; Tamura, Fumihiko   ; Schnase, A.; Yamamoto, Masanobu   ; Hasegawa, Katsushi; Shimada, Taihei ; Suzuki, Hiromitsu; Ezura, Eiji*; Hara, Keigo*; Toda, Makoto*; Omori, Chihiro*; Takagi, Akira*; Yoshii, Masahito*; Anami, Shozo*; Haga, Koichi*

We have been developing MA core for J-PARC Ring RF Cavity. From long run tests, we found that poor electrical isolation between layers caused damages to the cores. We improved the electrical isolation mainly by introducing a smooth tension control system to the winding process. The degree of the each core's electrical isolation was evaluated by the results of DC resistance and radial RF impedance measurements. After long run tests of all of the cores, we installed 10 RF cavities in a tunnel in May 2007 and beam commissioning was started from October 2007. Until now, total operation time of the RF cavities in the tunnel is about 1500 hours. To check the condition of the cores, we measured the RF cavity impedance at intervals of beam operations. The result of impedance measurements shows that no impedance reduction related to core damage was observed.