Izumi Sakai

Recent beam studies of the PoP FFAG proton synchrotron

The PoP (Proof of Principle) FFAG accelerator, which was the world first FFAG proton synchrotron, was constructed at KEK. After the first proton beam acceleration of FFAG, we studied various aspects of the PoP FFAG. The observed beam orbit shift during the acceleration was consistent with the simulation result. It was confirmed that the beam intensity increased about five times with multi-bunch injection. The horizontal acceptance of the PoP FFAG was estimated at about 4000 /spl pi/ mm.mrad experimentally.

Status of 150MeV FFAG synchrotron

The 150 MeV proton FFAG (fixed field alternating gradient) synchrotron has been developed for aiming to investigate the possibilities of various applications such as proton beam therapy. The construction started in September 2002, and almost completed recently. In the proceedings, the overview of construction and status of commissioning is to be reviewed

A NbTi Superconducting Dipole Magnet Installed in a Pressurized Helium II Cooling Bath

A double-bath pressurized helium II cryostat for an accelerator NbTi test dipole was constructed. Heat leakage into the cryostat was 5 W at 1.8 K. The dipole was excited in the cryostat. After several quenchings in pressurized helium II, the dipole achieved a highest central field of 6.75 T with an excitation current of 6.6 kA.

Opposite field septum magnet system for the separation of charged particle beams

The Japan Hadron Facility (JHF) accelerator complex comprises a 50-GeV main synchrotron, a 3-GeV rapid-cycling synchrotron, and a 400-MeV linac. The accelerators provide high-intensity, high-energy proton beams for various scientific fields. These high-intensity, high-energy accelerators, especially the 50-GeV main synchrotron, impose tight demands on the injection/extraction septum magnets for a thin structure, large aperture and high operating field. But to manufacture high field septum magnets on the condition of a large aperture is very difficult because of its extraordinarily strong electromagnetic force due to the self-field. To cope with these tight demands, new design concepts of septa are required. An opposite-field septum magnet system is one of the solutions to realize a thin septa or very high-field septum magnets.

Multi-orbit synchrotron with FFAG focusing for acceleration of high intensity hadron beams

A multi-orbit synchrotron (MOS) with fixed field alternating gradient (FFAG) focusing is attractive for acceleration of high intensity hadron beams because acceleration cycle could be increased. The magnetic field of MOS is static, therefore, the repetition rate of acceleration could be increased more than 10 times larger than that of ordinary rapid cycling synchrotron (RCS) if an efficient high voltage RF accelerating system becomes available. Recently, a new type of high gradient RF cavity (HGC) using high permeability magnetic alloy (MA) has been developed and MOS with FFAG focusing becomes very promising. In order to clarify the feasibility of rapid cycling MOS (RCMOS) experimentally, proof-of-principle (POP) machine, which accelerates protons up to 1 MeV with 1 kHz repetition, is under development. We have also made several designs on high intensity proton accelerators with RCMOS for various applications such as an accelerator driven system (ADS) as an energy breeder, a spallation neutron source and a proton driver for a muon collider.

New optics design of injection/fast extraction/abort lines of J-PARC main ring

The J-PARC Main Ring has three straight sections for injection, slow extraction and fast extraction. Injection line has been redesigned so as to give a higher reliability for the thin septa. The magnetic field can be reduced by adding an extra kicker. Alternative optics for the fast extraction with a larger acceptance has been proposed. In this design, the thin septa are replaced by kickers with a large aperture. Beam with an arbitrary energy can be aborted from opposite side from the fast extraction. An external abort line has been designed to deliver the beam aborted at an arbitrary energy to a dump just by using a static quadrupole doublet for the focus.

Development of FFAG Accelerator at KEK

The 150MeV proton FFAG accelerator is constructed and a beam is extracted at the final energy. This is the prototype FFAG for various applications such as proton beam therapy. We are now in preparation for using an extracted beam in the practical applications.

Design and Construction of FFAG Magnets for the ERIT System at KURRI

As an intense neutron source for the boron neutron capture therapy system, a FFAG storage ring with Energy/emittance Recovery Internal Target (ERIT) has been developed in the Kyoto University Research Reactor Institute (KURRI). In order to develop storage ring for ERIT scheme, the spiral sector and radial sector FFAG rings were designed and compared about performance in ERIT system. The 3-dimensional magnetic fields of these magnets were calculated with the field analysis code, TOSCA. The pole shape of magnet was carefully optimized checking the betatron tune. Tunes were computed by means of tracking simulations in field maps based on TOSCA models. In this paper, the FFAG magnet design for ERIT system and the construction of FFAG ring in KURRI are described.

Hardware R&D of the KEK/JAERI 50 GeV synchrotron fast extraction kicker magnets

The fast extraction kicker magnets of the 50 GeV synchrotron are now in an intensive R&D stage. In the 50 GeV ring, the fast extraction system is designed to deliver the 50 GeV beam to the downstream neutrino oscillation experiment beam line with the Super-Kamiokande detector. At the same time, the fast extraction line is required to function as a beam abort, in case of hardware failure during acceleration of the beam from 3 GeV to 50 GeV. In order to fulfill both demands, the extraction system is designed to accommodate bipolar beam extraction. A new technology to make the bipolar kicker magnet system, using a symmetric Blumlein pulse forming network (SBPFN) system, has been introduced. Its validity is being investigated, both theoretically and experimentally. R&D programs aimed at establishing some of the important technical elements in the fast extraction kicker system are presently in progress. This R&D includes experimental studies of the bipolar kicker principle and the development of IGBT switching modules that satisfy full switching capability of the designed current and voltage.

Beam extraction of the PoP FFAG with a massless septum

We propose a new extraction scheme with a massless septum magnet in FFAG accelerator, with which the DC beam can be extracted. The system consists of a combination of massless and ordinary septa without kickers. After passing through the massless septum, the beam tail is stretched by the field gradient of the massless septum magnet, and that can be extracted with an ordinary septum. From the result of the tracking simulation, the principle of the extraction scheme is verified. The result of the performance test of the massless septum indicates that the magnet works well as designed, and this scheme is feasible.