Kota Okabe

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.

Realizing a high-intensity low-emittance beam in the J-PARC 3-GeV RCS

The J-PARC 3-GeV rapid cycling synchrotron is now developing beam studies to realize a high-intensity lowemittance beam with less beam halo. This paper presents the recent experimental results while discussing emittance growth and its mitigation mechanisms.

Conceptual Design of Beam Dividing System for J-PARC Transmutation Experimental Facility

The Japan Proton Accelerator Research Complex (J-PARC) consists of three accelerators and three experimental facilities. In addition, new experimental facility for the Accelerator-driven system (ADS), the Transmutation Experimental Facility (TEF), is planned [1, 2]. The TEF is composed of two experimental facilities, Transmutation Physics Experimental Facility (TEF-P) and ADS Target Test Facility (TEF-T), and both facilities use the 400MeV proton beam from the LINAC [3, 4]. The LINAC is now operating in repetition of 25Hz for the 3GeV rapid-cycling synchrotron (RCS) and downstream facilities. Therefore in order to keep beam power for existing experimental facilities and furthermore to deliver the beam to the TEF, the LINAC should be operating in 50Hz and new beam dividing system will be installed at the upstream of the L3BT (LINAC to 3GeV RCS Beam Transport) straight section. The L3BT straight section of a doublet structure is adopted as the fundamental lattice, keeping the continuity of the transverse focusing scheme [5, 6]. The pulsed bending magnet, which is a main component of the beam dividing system, repeats between the unexcited and excited state in 25Hz, and divides the beam into the RCS and the TEF respectively. However, as a result of our early feasibility study, it is difficult to obtain the enough beam orbit separation at the doublet with the only pulsed bending magnet. Thus, the beam for the TEF is extracted with both the pulsed bending magnet and a static septum magnet. In this scheme, the doublet quadrupole magnets should be improved. In this presentation, we will report a conceptual design of the beam dividing system for the TEF.

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.

Recent Progress of 1-MW Beam Tuning in the J-PARC 3-GeV RCS

This paper presents the recent progress of 1-MW beam tuning in the J-PARC 3-GeV RCS, especially focusing on our approaches to beam loss issues.

The Path to 1 MW: Beam Loss Control in the J-PARC 3-GeV RCS

The J-PARC 3-GeV RCS started a 1-MW beam test in October 2014, and successfully achieved a 1-MW beam acceleration in January 2015. Since then, a large fraction of our effort has been concentrated on reducing and managing beam losses. In this paper, recent progresses of 1-MW beam tuning are presented with particular emphasis on our approaches to beam loss issues.

Performance Studies of the Vibration Wire Monitor on the Test Stand with Low Energy Electron Beam

In the high intensity proton accelerator as the J-PARC accelerators, serious radiation and residual dose is induced by a small beam loss such a beam halo. Therefore, diagnostics of the beam halo formation is one of most important issue to control the beam loss. For the beam halo monitor, the vibration wire monitor (VWM) has a potential for investigating the beam halo and weak beam scanning [1]. The principle of the VWM is to pick up the frequency shift of the vibration wire which is irradiated by a beam. The novelty of the method is that temperature shift of the wire provides information about the number of particles that interact with the wire. The VWM has a wide dynamic range, high resolution and the VWM is not susceptible to secondary electrons and electric noises. We have studied the VWM futures as a new beam-halo monitor on the test stands with low energy electron gun. The frequency shift of the irradiated vibration wire was conformed about various wire materials and the electron beam profile measured by using the VWM was consistent with the results of the faraday cup measurement. Also we calculated a temperature distribution on the vibration wire which is irradiated by the electron beam with the numerical simulation. The simulations have been fairly successful in reproducing the transient of the irradiated vibration wire frequency measured by test stands experiments. In this presentation, we will report a result of performance evaluation study for the VWM on the test stands and discuss about the VWM for beam halo diagnostic.

Study of the Charge Density Control Method including the Space Charge Effect in the Proton Synchrotron

For high intensity proton accelerators, one of the beam loss sources is the incoherent tune spread caused by the space charge force. In the 3 GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex, beams are injected sequentially and shifted slightly from the central orbit in order to increase the beam size intentionally and suppress the charge density and incoherent tune spread. This injection method has been adopted and suppressed the beam loss. However, simulations clarified that beams did not spread as much as expected because of the space charge effect in the high current case. As simulation results of the optimized beam shift pattern when the space charge effect is considered, it was obtained that the incoherent tune spread could be suppressed to an extent that has not been achieved previously.