T. Ueno

Improvement of the Shift Bump Magnetic Field for a Closed Bump Orbit of the 3-GeV RCS in J-PARC

The four shift bump magnets (BUHS01-04) of the 3-GeV RCS in J-PARC, which are located at the long straight section, produce a fixed main bump orbit to merge the injection beam into the circulating beam. They are realized with four magnets connected in series to form the accurate closed bump orbit. However, the total integrated magnetic field of the four magnets is not zero because of the magnetic field interference between the shift bump magnet and the adjacent quadrupole magnets (Q magnet). In order to measure the magnetic field distribution accurately, the short search coil and the long search coil were used. Furthermore, the imbalance of the total integrated magnetic field has been improvement by inserting 0.3 mm insulators in the median plane of the return yoke of the BUHS02 and 03. The value of the integration has been decreased from 2358.0 G ldr cm to -71.6 G ldr cm.

Magnetic Field Measurement of the Extraction Kicker Magnet in J-PARC RCS

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

Simulation Model for Design of a New Power Supply

The simulation model for a new power supply of the injection bump system magnets [1]-[4] of the 3-GeV RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Complex) [5], [6] has been constructed. The new power supply requires the reduction of the ripple noise current which will resonate with load and excites a forced beam oscillation at 96 kHz in the injection stage. In order to incorporate the load impedance in the simulation model, the impedances of a feeder line and the bump magnet with a ceramic vacuum chamber [7] inside were measured. The RF shield is formed on the ceramic surface along the beam direction. The results were successfully analysed using the OPERA-3D [8] and the circuit simulation code, Micro-Cap [9], and showed a good agreement. It was found the RF shield of a ceramic chamber has a resonant structure corresponding to 96 kHz.

Comparison of the Pulsed Power Supply Systems Using the PFN Switching Capacitor Method and the IGBT Chopping Method for the J-PARC 3-GeV RCS Injection System

Each pulsed power supply of the bending magnets of the 3-GeV Rapid Cycling Synchrotron injection area at the Japan Proton Accelerator Research Complex has been designed and manufactured for the painting injection in the transverse plane. The magnet currents of both the shift bump magnet and the pulsed steering magnet have a shape of trapezoidal waveform, the flat-top part of which is used for beam injection. The horizontal and vertical painting bump magnets change the beam orbit by using a decaying waveform of the magnet current dynamically. The system with a pulse forming network switching capacitor produces lower current ripples due to the limited number of switchings for the waveform formations. On the other hand, the system of an Insulated Gated Bipolar Transistor chopping system cannot be free from ripple generation due to the continuous switching. However, the Insulated Gated Bipolar Transistor chopping method has an advantage, which produces any shape of required waveform. This paper summarizes the comparison of these power supply systems from view point of the switching noises.

Field Measurement of DC Magnets at 3-GeV RCS in J-PARC

The J-PARC RCS (rapid cycling synchrotron) is designed to inject the beam from the LINAC, to change their charge from to , to accelerate the beam from 400 MeV to 3 GeV, with protons per pulse at 25 Hz repetition rate, and to extract the beam after the acceleration to the MLF (material and life science experimental facility) and the MR (main ring). Thus the RCS has the beam circulating ring and three beam transport lines. The RCS ring consists of several magnets, and the DC magnets are installed for beam injection and extraction. The four steering magnets and two septum magnets are installed at injection line in order to adjust the beam injection point. One quadratic magnet, two steering magnet and two septum magnets are installed at dump line for the part of the beam with their charge not changed from to at the charge stripping foil. Two deflecting magnets to kick out the beam without exciting the pulse kicker magnets and three septum magnets are installed at the extraction line. Up to now, the DC magnets are developed and manufactured, the field measurements are carried out, and magnets installation into the RCS tunnel are finished. The field distributions of DC magnets are measured by using the new field mapping system with three one-dimensional hall-probes on a 3-axis movable stage. In the case of the quadrupole magnet, the field measurements are not only field mapping but also analyze its magnetic higher order components by the harmonic rotating coil. As a result, the measured field quality meets the design performance requirements of the DC magnets.

Design and Construction of Septum Magnets at 3-GeV RCS in J-PARC

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.

Field Measurement of Pulse Steering Magnet for J-PARC 3 GeV Rapid Cycling Synchrotron

J-PARC 3-GeV Rapid Cycling Synchrotron (RCS) has two functions: as a proton beam driver to the spallation neutron source at the Material and Life Science Facility (MLF) and also as an injector to the Main Ring (MR). However the required beam parameters for each facility are different. The pulse steering magnet (PSTR) was developed to satisfy these requirements by switching the painting area in each acceleration cycle of MLF and MR and to realize center injection at 400 MeV. Therefore there are two operation modes, painting injection and center injection, for operation of PSTR.