VARIOUS USAGES OF WALL CURRENT MONITORS FOR COMMISSIONING OF RF SYSTEMS IN J-PARC SYNCHROTRONS

Wall current monitors (WCM) for rf system commissioning are installed in the J-PARC synchrotrons, the RCS and the MR. The WCM signals are used as the input of the beam loading compensation system, and also used for diagnostics to adjust the rf system parameters. Since the rf and beam frequencies are in the range of a few MHz and several ten MHz, direct measurement of the WCM signals is possible. For the diagnosis, the WCM signals are taken by an oscilloscope with the revolution clock signal generated by the low level rf (LLRF) control system, and slices of the WCM waveform with lengths of the revolution periods are generated. By stacking the slices, one can get a mountain plot, which shows motions of bunches and variations of the bunch shapes. Also, time variations of the bunching factor, which are important for acceleration of high intensity proton beams, are obtained. The harmonic analysis is performed on the WCM signal and the cavity voltage monitor signal. By using complex amplitudes of them, one can calculate the impedance seen by the beam. We show examples of the analyzes described above. The rf parameters for high intensity beams have been successfully adjusted by using these analysis methods.