J-PARC RCS non-linear frequency sweep analysis

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

A standard way to measure the transfer function of a system of amplifier and cavity uses a network analyzer and a linear frequency sweep. However, to check the transfer function of the broadband (Q=2) RCS RF system, we analyze several harmonics at same time under real high power ramp conditions. A pattern driven DDS generates frequency and amplitude like in accelerator operation. During the 20ms acceleration time, a large memory oscilloscope captures the RF-signals. The data are processed offline like down conversion in a multi-harmonic LLRF-system, giving multi-harmonic amplitude and phase information. With this setup we could find and cure resonances before installation to the tunnel. RCS is in the commissioning phase and has reached the milestone of acceleration to final energy and beam extraction. 10 RF systems are in operation. The LLRF-system controls fundamental h(2) and 2nd harmonic h(4). The multiharmonic analysis allows to check the RF system behavior also at other harmonics.