Kazami Yamamoto

The JKJ Lattice

The JKJ high‐intensity proton accelerator facility consists of a 400‐MeV linac, a 3‐GeV 1‐MW rapid‐cycling synchrotron and a 50‐GeV 0.75‐MW synchrotron. The lattice and beam dynamics design of the two synchrotrons are reported.

Path to 1-MW at J-PARC Rapid Cycling Synchrotron

The accelerator system at Japan Proton Accelerator Research Complex (J-PARC) has been operational since May 2008 and has mainly been used to perform physics experiments. The accelerator system consists of a Linac, a Rapid Cycling Synchrotron (RCS), and a Main Ring Synchrotron. The originally designed RCS injection energy is 400MeV, but the first operation started at 181MeV. New acceleration cavities were installed in J-PARC Linac during the summer shutdown of 2013, and user operation by the Material and Life science Facility (MLF) at the injection energy of 400MeV was started from February 2014. Post beam commissioning of 400MeV injection energy, beam loss was small enough, and we established 300kW continuous operation. Subsequently, the peak current of the Linac was increased from 30mA to 50mA. This upgrade enabled us to try 1-MW beam acceleration. Finally, after some additional improvements, we successfully accelerated 1-MW equivalent protons.

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.

The Evaluation of the Residual Dose Caused by the Large-Angle Foil Scattering Beam Loss for the High Intensity Beam Operation in the J-PARC RCS

The Japan Proton Accelerator Research Complex 3-GeV rapid cycling synchrotron (RCS) has adopted the multi-turn charge-exchange injection scheme that uses H beams. During injection, both the injected and circulating beams scatter from the charge-exchange foil. Therefore, the beam loss caused by the large-angle scattering from the foil occurs downstream of the injection point. For countermeasure against the uncontrolled beam loss, a new collimation system was developed and installed in the summer shutdown period in 2011. During beam commissioning, this uncontrolled beam loss was successfully localized for a 300 kW beam. Since the present target power of the RCS is 1 MW, the accurate simulation model to reproduce experimental results has been constructed in order to evaluate residual dose at higher power operation.

Measurement system of the background proton in DeeMe experiment at J-PARC

In particle physics, various theories beyond the standard model predict the existence of the –e conversion process, but it remains undetected due to its low probability. The DeeMe experiment proposed at the J-PARC Material Life Science Facility is designed to detect the –e conversion process by using the muon-production target. During the DeeMe experiment, to distinguish the –e event signal from a background, less than one proton per hour should arrive from the main beam after a few hundreds of nanoseconds. We designed a new measurement system to confirm that such a low background is attained. A simulation indicates that the new system is sufficiently sensitive to detect the delayed protons.

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.

The Status of Optics Design and Beam Dynamics Study in J-PARC RCS

The 3GeV RCS at J-PARC is designed to provide the 3GeV proton beam and a goal of output beam power is 1MW. The beam commissioning starts on May 2007. At present more qualitative studies concerning beam dynamics are in progress: core beam handlings, halo beam handlings, instabilities and so on. In this paper the RCS optics design and the present status of beam dynamics studies are summarized.

MARS14 Collimation and Shielding Studies for the 3 GeV Ring of J‐PARC Project

MARS14 Monte Carlo simulations were performed for collimation and shielding studies of the J‐PARC 3 GeV ring. A 400 MeV proton beam loss distribution, calculated with the STRUCT code, was used as a source term. The module locations in the ring and the curved tunnel sections were described by the MAD‐MARS beam line builder and a deep penetration calculation with good statistics was carried out using a 3‐dimensional multi‐layer technique. Prompt dose‐rate distributions were calculated inside and outside the concrete and soil shield, and an effective shielding design was made. The residual dose rates for various beam line materials were also calculated to estimate the external‐exposures during maintenance. In this paper, the calculation results are exemplified for the region from the injection through the collimator.