Y. Irie

Design of the Shift Bump Magnets for the Beam Injection of the 3-GeV RCS in J-PARC

The injection system of the 3-GeV RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Research Complex) consists of four main orbit bump magnets (shift bump) to merge the injection beam with the circulating beam. In order to control the injection beam with sufficient accuracy, the shift bump magnets need a wide uniform magnetic field. The magnetic field design and the structural analysis of the shift bump magnets have been performed using three-dimensional electromagnetic and mechanical analysis codes. The shift bump magnets have realized a uniform field with less than 0.35% inhomogeneity over a wider area, which is 400 mm in width and 240 mm in height. Furthermore, the magnets operate with a high magnetic field and they are located in high radioactive level area. The flexible bar is applied to the coil as the countermeasure for thermal expansion and the insulator has strong radiation resistance

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.

Design and Preliminary Performance of the New Injection Shift Bump Power Supply at the J-PARC 3-GeV RCS

A new power supply for the injection shift bump magnet at the Japan Proton Accelerator Research Complex 3-GeV Rapid Cycling Synchrotron has been designed with the energy upgrading of the linear accelerator to 400 MeV. The power supply is required to output the maximum current of 32 kA, which is 1.6 times the present current. Moreover, peak current ripple noise should be less than ±0.2% of the setting current in a range from 10 kA to 32 kA output current. The insulated gate bipolar transistor chopping system in the present power supply produces the continuous current ripple noise due to the switching, which resonates with the load and excites a forced beam oscillation at about 96 kHz in the injection stage. So, the circuit structure of the new power supply has been changed from the insulated gate bipolar transistor chopping system to the pulse forming network system by switching capacitors. The whole power supply is comprised of 16 banks, each of which outputs 2 kA at 13.2 kV maximum. The first bank has been manufactured and the characteristics were evaluated in the factory. This paper summarizes the design and the preliminary experimental results of the new power supply.

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.

Design of Thick Septa Magnets Based on 3D Field Calculation for the 3 GeV Rapid Cycling Synchrotron of J-PARC

Septum magnets are used in the injection and extraction section of the 3 GeV rapid cycling synchrotron (RCS) of J-PARC (Japan Proton Accelerator Research Complex). The RCS needs seven septum magnets, two for the injection line, two for the beam dump line and three for the extraction line, respectively. These septa require a large aperture for low-loss operation with high intensity beams, and high durability for minimizing maintenance after high activation. For insuring mechanical stability the septum magnets have been designed to work DC. The septa magnets work outside a vacuum, thus eliminating any trouble due to the leakage of cooling water into the vacuum system. We have been designing them by using the three dimensional magnet static field calculation code, TOSCA. This paper describes the flatness of the magnetic field in the gap and reduction of the leakage field of the septum magnets in the RCS

H/sup -/ painting injection system for the J-PARC 3-GeV high intensity proton synchrotron

The J-PARC Project 3-GeV proton synchrotron is designed to accelerate 8.3 /spl times/ 10/sup 13/ protons per pulse at a 25 Hz repetition rate for the injection energy of 400 MeV. The incoming beam emittance of the 400-MeV linac is 4/spl pi/ mm mrad and the acceptance in the 3-GeV synchrotron is 324/spl pi/ mm mrad in both the horizontal and vertical planes. Painting injection system is designed to fit in the FODO structure, which has rather short drift space. The bump orbit for painting injection is designed to have a full acceptance of the circulating orbit through the injection period. A full-acceptance bump orbit will enable both correlated and anti-correlated painting injection.

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.

Spallation neutron source (SNS) diamond stripper foil development

Diamond stripping foils are under development for the SNS. Freestanding, flat 300 to 500 mug/cm2 foils as large as 17 x 25 mm2 have been prepared. These nano-textured polycrystalline foils are grown by microwave plasma- assisted chemical vapor deposition in a corrugated format to maintain their flatness. They are mechanically supported on a single edge by a residual portion of their silicon growth substrate; fine foil supporting wires are not required for diamond foils. Six foils were mounted on the SNS foil changer in early 2006 and have performed well in commissioning experiments at reduced operating power. A diamond foil was used during a recent experiment where 15 muC of protons, approximately 64% of the design value, were stored in the ring. A few diamond foils have been tested at LANSCE/PSR, where one foil was in service for a period of five months (820 C of integrated injected charge) before it was replaced. Diamond foils have also been tested in Japan at KEK (640 keV H) where their lifetimes slightly surpassed those of evaporated carbon foils, but fell short of those for Sugais new hybrid boron carbon (HBC) foils.

Intensity dependent emittance-exchange in a high intensity proton synchrotron

The acceptance of the KEK booster has large side value (272 /spl pi/ nm mrad in the horizontal plane and 61/spl pi/ mm mrad in the vertical plane). To increase the beam intensity we have been trying to achieve painting injection in the horizontal plane. The intensity-dependent emittance exchanges in the horizontal and vertical plane were measured by a method using a scraper and bump magnets method. In order to clarify the experimental results, multiparticle tracking was performed with self-consistent space-charge forces. The experimental and simulation results imply that a space-charge potential of a beam-induced coupling exists between the horizontal and vertical planes.

Beam position measurement using linac microstructure at the KEK booster synchrotron

The position information of the most recently injected beam from the linac is obtained by picking-up the signal of the harmonic component of the beam, if the bunch structure disappears during one turn due to the momentum spread. The experiment for 201 MHz pickup was performed in the KEK booster ring, and is compared with the simulation. The possible application of this method to the 3 GeV rapid cycling synchrotron in the Japan Proton Accelerator Research Complex (J-PARC) is also addressed.