3 GeV RCS (Rapid Cycling Synchrotron) at J-PARC (Japan Proton Accelerator Research Complex) comprises with several magnets of different kinds. These include seven septum magnets for the beam injection and extraction at RCS ring. Design requirements for these magnets often conflicts with efforts to minimize leakage magnetic field. Silicon steel sheets set outside of the septum magnets shield leakage magnetic fields so as to keep proper beam orbits in the ring in most cases. At the beam junction areas for beam injection and extraction, sufficient spacing is not available for installing thick magnetic shields. Vacuum chambers are made by the magnetic stainless steel to reduce the leakage field without a large shield. Results obtained from 3-D field calculations by TOSCA indicate the magnetic leakage field is suppressed down to a few Gauss or less in the present design.All septum magnets and branch structure vacuum chamber made of titanium and magnetic stainless steel are manufactured and assembled successfully. The field measurements of the septum magnets proved that both the strength and also gradient of the magnetic leakage field are diminished.Index Terms-Leakage field, magnetic vacuum chamber, proton synchrotron, septum magnet.
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.
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