DESIGN AND PERFORMANCES OF PHASE MONITOR IN J-PARC LINAC

J-PARC linac employs a fast current transformer (FCT) as a beam phase monitor to calculate the beam energy by time-of-flight method, and the 4-stripline beam position monitors (BPMs) for the beam position measurement. We designed, fabricated and have been used them to the beam operation. Performances of fabricated monitors and their calibration data have been measured. Here, we will discuss the structure and frequency performance of the FCT monitor. At the great earthquake occurred off the Pacific coast of Tohoku, some CT monitors, such as a phase monitor and beam current monitor had damage and the vacuum leakage was observed. But no damage of BPMs was found. It has been considered that the signals from striplines of BPM would be useful for a phase measurement. A phase measurement using a BPM has been successfully conducted. Above the lessons learnt from the damage by the quake, we consider to employ the BPM for the FCT backups after evaluation of the performances of BPM as the phase measurement device. Finally, these performances of BPM are compared with those of FCT. Based on the results of the evaluations, we will discuss the performance to measure the beam phase both FCT and BPM.