Kicker magnets in the J-PARC (Japan Proton Accelerator Research Complex) RCS (Rapid Cycling Synchrotron) are being constructed at JAERI (Japan Atomic Energy Research Institute) as the extraction pulse magnet. They kick the accelerated 3 GeV proton beam to the following extraction line at a repetition rate of 25 Hz. The kicker magnet is a distributed-parameter line type in order to obtain a fast rise time of the magnetic field. It is also designed with a large aperture in order to accept a maximum beam power of 1 MW. Therefore, impedance mismatch and fringe fields have a large distorting effect on the flatness of the kicker magnetic field. We examined these effects by simulation and measurement, and contrived to improve the field flatness. In this paper, we present the characteristic features of the RCS kicker systems, describe our magnetic field measurement and improvement, and briefly introduce the field mapping which we are performing now.Index Terms-J-PARC, kicker magnet, magnetic field, RCS.
Kicker magnets are installed in the extraction section of the RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Research Complex) facility. They extract a 3 GeV proton beam and inject it into a downstream beam transport line at a repetition rate of 25 Hz. The power supply is mainly composed of the charging unit, the pulse forming network, and thyratrons as switching device. The maximum charging voltage is 80 kV. The kicker magnet is a distributed (transmission line) twin-C type. The circuit parameters are designed to have the 10 characteristic impedance. The magnets are installed in vacuum chambers to prevent voltage breakdown. In order to accept 1 MW beam power, strict conditions are imposed on the kicker system. In the first part of this paper, we give an outline of the RCS extraction kicker system. Next, we report the specifications and performance of the power source and magnet. In addition, we report the measurements of the vacuum performance and magnetic field.Index Terms-J-PARC, kicker magnet, RCS, thyratron, vacuum.
Installation of the kicker magnets in the extraction section of the RCS in J-PARC facility was completed. They extract a proton beam accelerated up to 3GeV. Since high voltage of 30 kV, which corresponds to 60 kV for charging the pulse forming line, is applied to the magnet every 40 msec, they are installed in vacuum chambers to prevent the electrical breakdown. However, magnetic field mapping is difficult in vacuum. Therefore, we performed the mapping in the air with applying one third of the operational voltage after checking linear dependence of magnetic field to exciting current. A short search coil on the 3-axis stages was used in the magnetic field mapping. The results showed that the good uniformity was achieved in the whole aperture. The magnetic field distribution of the same type of kicker magnet was in good agreement with each other. The excitation test with the operational charging voltage of 60 kV was also performed in vacuum. At the first stage, we were bothered by the electric breakdown. It was noticed that the reduction of outgassing rate by baking was very effective to suppress the discharge. And the continuous excitation was found to have a conditioning effect for the stable operation.Index Terms-Accelerator magnet, magnetic field measurement, vacuum breakdown.
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