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Journal Articles

Beam dynamics design of the muon linac high-beta section

Kondo, Yasuhiro; Hasegawa, Kazuo; Otani, Masashi*; Mibe, Tsutomu*; Yoshida, Mitsuhiro*; Kitamura, Ryo*

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.2304 - 2307, 2017/06

A muon linac development for a new muon g-2 experiment is now going on at J-PARC. Muons from the muon beam line (H-line) at the J-PARC MLF are once stopped in an silica aerojel target and room temperature muoniums are evaporated from the aerogel. They are dissociated with laser (ultra slow muons), then accelerated up to 212 MeV using a linear accelerator. For the accelerating structure from 40 MeV, disk-loaded traveling-wave structure is applicable because the particle beta is more than 0.7. The structure itself is similar to that for electron linacs, however, the cell length should be harmonic to the increase of the particle velocity. In this paper, the beam dynamics design of this muon linac using the disk-loaded structure is described.

Journal Articles

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

Hotchi, Hideaki; Harada, Hiroyuki; Kato, Shinichi; Okabe, Kota; Saha, P. K.; Shobuda, Yoshihiro; Tamura, Fumihiko; Tani, Norio; Watanabe, Yasuhiro; Yoshimoto, Masahiro

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.2470 - 2473, 2017/06

For this past year, RCS beam tuning was focused on realizing a high-intensity low-emittance beam required from the downstream facility. The extraction beam emittance including its tail part was successfully decreased by optimizing transverse injection painting, and tune and chromaticity manipulations, where bipolar sextupole field patterns were newly introduced to simultaneously achieve emittance growth mitigation at the early stage of acceleration and beam instability suppression after the middle stage of acceleration. This paper presents the recent experimental results, together with detailed discussions for the emittance growth and its mitigation mechanisms.

Journal Articles

Beam position measurement during multi-turn painting injection at the J-PARC RCS

Hayashi, Naoki; Saha, P. K.; Yoshimoto, Masahiro; Miura, Akihiko

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.277 - 280, 2017/06

Multi-turn painting injection scheme is important for high intensity proton accelerators. At the J-PARC RCS, a transverse painting scheme was adapted by adding vertical painting magnets to the beam transport line before the injection point, with horizontal painting being performed by a set of dedicated pulse magnets in the ring. To establish a transverse painting condition, it is usual to base on the pulse magnet current pattern. However, it is more desirable to directly measure the beam orbit time variation for evaluation. A linac beam was chopped to match the ring RF bucket. We thought that it would be difficult to measure the position for each pulse; however, the average position could be extracted by introducing a particular device. For the beam injected into the ring, because the linac RF frequency component was diminished due to debunching quickly, one could determine its position in the beginning of the injection period. However, due to rebunching effect the position determination becomes difficult. This problem needs to be resolved.

Journal Articles

Crossbar H-mode drift-tube linac design with alternative phase focusing for muon linac

Otani, Masashi*; Futatsukawa, Kenta*; Hasegawa, Kazuo; Kondo, Yasuhiro; Kitamura, Ryo*; Kurennoy, S.*

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.2868 - 2870, 2017/06

We have developed a Crossbar H-Mode (CH) drift-tube linac (DTL)design with an alternative phase focusing (APF) scheme for a muon linac, in order to measure the anomalous magnetic moment and electric dipole moment (EDM) of muons at the Japan Proton Accelerator Research Complex (J-PARC). The CH-DTL accelerates muons from $$beta$$ = v/c = 0.08 to 0.28 at an operational frequency of 324 MHz. The design and results are described in this paper.

Journal Articles

First trial of the muon acceleration for J-PARC muon g-2/EDM experiment

Kitamura, Ryo*; Otani, Masashi*; Fukao, Yoshinori*; Kawamura, Naritoshi*; Mibe, Tsutomu*; Miyake, Yasuhiro*; Shimomura, Koichiro*; Kondo, Yasuhiro; Hasegawa, Kazuo; Bae, S.*; et al.

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.2311 - 2313, 2017/06

Muon acceleration is an important technique in exploring the new frontier of physics. A new measurement of the muon dipole moments is planned in J-PARC using the muon linear accelerator. The low-energy (LE) muon source using the thin metal foil target and beam diagnostic system were developed for the world's first muon acceleration. Negative muonium ions from the thin metal foil target as the LE muon source was successfully observed. Also the beam profile of the LE positive muon was measured by the LE-dedicated beam profile monitor. The muon acceleration test using a Radio-Frequency Quadrupole linac (RFQ) is being prepared as the first step of the muon accelerator development. In this paper, the latest status of the first muon acceleration test is described.

Journal Articles

Simulation studies of transverse beam instabilities and measures beyond 1 MW beam power in the 3-GeV RCS of J-PARC

Saha, P. K.; Shobuda, Yoshihiro; Hotchi, Hideaki

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.3750 - 3752, 2017/06

Journal Articles

Improvements of vacuum system in J-PARC 3 GeV synchrotron

Kamiya, Junichiro; Hikichi, Yusuke*; Namekawa, Yuya*; Takeishi, Kenichi; Yanagibashi, Toru*; Kinsho, Michikazu; Yamamoto, Kazami

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.3408 - 3411, 2017/06

The RCS vacuum system has been upgraded since the completion of its construction towards the objectives of both better vacuum quality and higher reliability of the components. For the better vacuum quality, (1) pressure of the injection beam line was improved to prevent the H$$^{-}$$ beam from converting to H$$^{0}$$; (2) leakage in the beam injection area due to the thermal expansion was eliminated by applying the adequate torque amount for the clamps; (3) new in-situ degassing method of the kicker magnet was developed. For the reliability increase of the components, (1) A considerable number of fluoroelastmer seal was exchanged to metal seal with the low spring constant bellows and the light clamps; (2) TMP controller for the long cable was developed to prevent the controller failure by the severe electrical noise; (3) A number of TMP were installed instead of ion pumps in the RF cavity section as an insurance for the case of pump trouble.

Journal Articles

Multipactor problem of J-PARC SDTL

Ito, Takashi; Morishita, Takatoshi; Tamura, Jun; Nammo, Kesao*; Sugimura, Takashi*

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.4184 - 4186, 2017/06

We have suffered from multipactor problem of some SDTLs after the Great East Japan Earthquake. As a designed operating rf power of the SDTL is in the multipactor region, we had to operate at higher power of the designed one. From the result of the simulation and the observation of the SDTL cavity, it became clear that the multipactor occurred on the inner surface of the cavity. We think that one of the cause of the multifactor is the contamination on the inner surface of the cavity, we performed the cleaning of the inner surface of the cavity by using acetone. The cleaning was very effective and the multipactor region was reduced or disappeared. The multipactor problem has not occurred since then.

Journal Articles

Stabilization of timing system operation of J-PARC Linac and RCS

Takahashi, Hiroki; Hayashi, Naoki; Ito, Yuichi*; Kawase, Masato*; Sawabe, Yuki*

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.4000 - 4002, 2017/06

The timing system data (delay value, status, etc.) of J-PARC Linac and rapid cycling synchrotron is managed by a computer. After updating this hardware, we encountered the problem of data corruption in the timing system. Therefore, we added a function to the software for the timing system VME and investigated the cause of the problem. The investigation results showed a problem with the network connected PCI-Express reflective memory. We implemented measures for stabilizing the timing system operation based on this result.

Journal Articles

Performance and status of the J-PARC accelerators

Hasegawa, Kazuo; Hayashi, Naoki; Oguri, Hidetomo; Yamamoto, Kazami; Kinsho, Michikazu; Yamazaki, Yoshio; Naito, Fujio*; Koseki, Tadashi*; Yamamoto, Noboru*; Hori, Yoichiro*

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.2290 - 2293, 2017/06

The J-PARC is a high intensity proton facility and the accelerator consists of a 400 MeV linac, a 3 GeV Rapid Cycling Synchrotron (RCS) and a 30 GeV Main Ring Synchrotron (MR). We have taken many hardware upgrades such as front end replacement and energy upgrade at the linac, vacuum improvement, collimator upgrade, etc. The beam powers for the neutrino experiment and hadron experiment from the MR have been steadily increased by tuning and reducing beam losses. The designed 1 MW equivalent beam was demonstrated and user program was performed at 500 kW from the RCS to the neutron and muon experiments. We have experienced many failures and troubles, however, to impede full potential and high availability. In this report, operational performance and status of the J-PARC accelerators are presented.

Journal Articles

Coupled bunch instability and its cure at J-PARC RCS

Shobuda, Yoshihiro; Saha, P. K.; Hotchi, Hideaki; Harada, Hiroyuki; Takayanagi, Tomohiro; Tamura, Fumihiko; Tani, Norio; Togashi, Tomohito; Toyama, Takeshi*; Watanabe, Yasuhiro; et al.

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.2946 - 2949, 2017/05

no abstracts in English

Journal Articles

Detection of H$$^{0}$$ particles in MEBT2 chicane of J-PARC linac

Tamura, Jun; Miura, Akihiko; Morishita, Takatoshi; Okabe, Kota; Yoshimoto, Masahiro; Ao, Hiroyuki*; Futatsukawa, Kenta*; Maruta, Tomofumi*; Miyao, Tomoaki*; Nemoto, Yasuo*

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.2308 - 2310, 2017/05

In the Japan Proton Accelerator Research Complex (J-PARC), H$$^{0}$$ particles generated by collisions of accelerated H$$^{-}$$ beams with residual gases are considered as one of the key factors of the residual radiation in the high energy accelerating section of the linac. To diagnose the H$$^{0}$$ particles, the new analysis line for the H$$^{0}$$ particles was installed in the matching section from the separated-type drift tube linac (SDTL) to the annular-ring coupled structure linac (ACS). In the analysis line, the accelerated H$$^{-}$$ ions travel in chicane orbit by the four dipole magnets. In the beam commissioning, we directly detected the H$$^{0}$$ particles by using a carbon plated installed to a wire scanner monitor and indirectly detected the H$$^{0}$$ particles by using a scintillation detector. We also confirmed that the signals change with vacuum condition in the SDTL section.

Journal Articles

New injection scheme of J-PARC rapid cycling synchrotron

Yamamoto, Kazami; Kamiya, Junichiro; Saha, P. K.; Takayanagi, Tomohiro; Yoshimoto, Masahiro; Hotchi, Hideaki; Harada, Hiroyuki; Takeda, Osamu*; Miki, Nobuharu*

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.579 - 581, 2017/05

The 3-GeV Rapid Cycling Synchrotron of Japan Proton Accelerator Research Complex aims to deliver 1-MW proton beam to the neutron target and Main Ring synchrotron. Present beam power of the Rapid Cycling Synchrotron is up to 500-kW and the higher radiation doses were concentrated in the injection area. These activations were caused by the interaction between the foil and the beam. To reduce the worker dose near the injection point, we have studied a new design of the injection scheme to secure enough space for radiation shielding and bellows. In the new system, two of four injection pulse bump magnets are replaced and we are able to ensure the additional space around the injection foil chamber. So far, new injection system seems not impossible. However, preliminary study result indicated that temperature of the duct and shielding metals would be slightly higher. The eddy current due to the shift bump magnet field generates heat. Thus we have to study details of above effect.

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