Upgrade of power supply system for RF-chopper at J-PARC linac

In the J-PARC Linac, the radio frequency deflector was adopted as a chopper to capture the particles into the RF-bucket in the next synchrotron. The chopper, consists of two deflectors, was installed on the medium-energy beam-transport line. In the operation of the RF-chopper, the fast rise/fall time of the pulse is a fundamental requirement to minimize the beam loss. In the previous system, the two series coupled chopper deflectors were driven by one solid-state amplifier due to the cost. However, the fell time indicated a poor result to effect the ringing into each cavity. Therefore, the additional solid-state amplifier and low level RF system were installed in the summer 2012 and the connection changed to the parallel system from the series using two amplifiers. The rise/fall time of the chopped beam was about 20 nsec in the beam current of 15 mA and the effect of the ringing was decreased. (author)