Energy measurement and correction for stable operation in J-PARC

Abstract

In Japan Proton Accelerator Research Complex (J-PARC), the beam accelerated up to 400MeV in the Linac is injected to 3 GeV rapid cycling synchrotron (RCS), and we realize the high intensity beam by using multi-turn injection. During a user operation, we rarely detected the beam loss at the high dispersion area in the RCS or the beam collimator section in the extraction beam transport line. These incidents indicate that the beam loss is caused by the momentum shift of RCS injection beam according to the experimental and simulated data. In the beam commissioning, we check the Linac beam momentum just before a user operation of the RCS. However, we could not previously measure the Linac beam momentum during the user operation because we adopt the multi-turn injection with synchrotron oscillation for longitudinal plane. Therefore, we measured the beam momentum in the beam injection line of the RCS. Because the Linac-to-3-GeV-RCS Beam Transport line (L3BT) has the high dispersion areas, we estimated the RCS-injection momentum from the beam orbit data by the Beam Position Monitors (BPMs). We measured the beam position data by these BPMs, and estimated the momentum shift by using the data and beam simulation. As a result, we found the momentum fluctuation during the user operation, and the fluctuation ∆p/p was shifted up to 0.1% from the reference. In addition, to suppress this beam loss induced by the momentum fluctuation and shift, we developed the momentum correction system. The fluctuation was achieved less than ±0.02 % with this system. Finally, the beam loss incidents induced by the beam momentum shift does not occur, and we successfully achieved the more stable user operation in J-PARC.