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Journal Articles

Two-parameter model for optimizing target beam distribution with an octupole magnet

Meigo, Shinichiro; Oi, Motoki; Fujimori, Hiroshi*

Physical Review Accelerators and Beams (Internet), 23(6), p.062802_1 - 062802_24, 2020/06

 Times Cited Count:0 Percentile:100(Physics, Nuclear)

As hadron accelerators for such as the ADS and spallation neutron source achieve increasing beam power, damage to targets is becoming increasingly severe. To mitigate this damage, nonlinear beam optics based on octupole magnets is attractive. Nonlinear optics can decrease the beam-focusing hazard due to failure of the rastering magnet. As a side effect of nonlinear optics, the beam size is known to expand drastically compared with linear optics. Nonlinear effects have been studied via a simplified filament model that ignores beam-divergence spread at the octupole magnet. In this study, a new generalized model is proposed for application to an octupole magnet, regardless of the filament-model approximation. It is found that the transverse distribution obtained by beam tracking can be specified by the introduction of only two parameters, namely the normalized octupole strength of $$K^{*}_8$$ and the $$cot phi$$ of the phase advance. To achieve the two antagonistic requirements of reduction of the beam-peak density and minimization of the beam loss, the transverse distribution is surveyed for a large range of beam position. It is found that a bell-shaped distribution with $$K^{*}_8 sim$$ 1 and $$cot phi sim$$ 3 can satisfy requirements. This result is applied to beam transport in the spallation neutron source at J-PARC. The calculation result given by the present model shows good agreement with the experimental data, and the peak current density is reduced by 50% compared with the linear-optics case.

Journal Articles

Beam monitor data analysis of interlocked events at J-PARC RCS

Hayashi, Naoki; Yoshimoto, Masahiro; Moriya, Katsuhiro; Hatakeyama, Shuichiro*

Proceedings of 16th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1096 - 1100, 2019/07

It is necessary to understand the reason why the accelerator has been interrupted due to beam loss or other machine mal function in order to keep high availability in long term period. At J-PARC RCS, 25 Hz rapid-cycling synchrotron, there is a system to record beam intensity and beam loss monitor signal for all pulses with 10 ms period. At this time, in addition, new system to archive data with better time resolution if interlocked events occurred has been introduced. Using these archived data, the events only RCS BLM gives MPS have been analyzed and it turns out that these events are related to the ion source discharge which makes very low intensity within less than a second. In this paper other typical events are presented and discuss how to improve the accelerator performance in future.

Journal Articles

Analysis of interlocked events based on beam instrumentation data at J-PARC Linac and RCS

Hayashi, Naoki; Hatakeyama, Shuichiro; Miura, Akihiko; Yoshimoto, Masahiro; Futatsukawa, Kenta*; Miyao, Tomoaki*

Proceedings of 7th International Beam Instrumentation Conference (IBIC 2018) (Internet), p.219 - 223, 2019/01

J-PARC is a multi-purpose facility. Accelerator stability is the one of important issues for users of this facility. To realize stable operation, we must collect data on interlocked events and analyze these data to determine the reasons for the occurrence of such events. In J-PARC Linac, data of interlocked events have been recorded using several some beam loss monitors and current monitors, and these data have been are analyzed and classified. In J-PARC RCS, new instrumentation is being introduced to obtain beam position. We discuss the present status and future plans related to this subject.

Journal Articles

Beam-loss monitoring signals of interlocked events at the J-PARC Linac

Hayashi, Naoki; Kato, Yuko; Miura, Akihiko; Futatsukawa, Kenta*; Miyao, Tomoaki*

Proceedings of 5th International Beam Instrumentation Conference (IBIC 2016) (Internet), p.368 - 371, 2017/03

It is important to understand why the beam loss occurs during user operation. It is understandable that the beam loss results from RF cavities failure. However, it would be still useful to study the beam loss detailed mechanism and to know which beam loss monitor (BLM) experiences the highest loss or is most sensitive. This may lead a reduction in the number of interlocked events and a more stable accelerator operation. The J-PARC Linac BLM has a simple data recorder that comprises multiple oscilloscopes. Although its functionality is limited, it can record events when an interlock is triggered. Of particular interest here are the events associated with only the BLM Machine Protection System (MPS). These may reveal hidden problems with the accelerator.

Journal Articles

A Malfunction of the beam collimator system in J-PARC 3 GeV rapid cycling synchrotoron

Yamamoto, Kazami; Okabe, Kota; Kamiya, Junichiro; Yoshimoto, Masahiro; Takeda, Osamu; Takayanagi, Tomohiro; Yamamoto, Masanobu

Proceedings of 13th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.314 - 318, 2016/11

The 3 GeV Rapid-Cycling Synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) project generates 1MW proton beam for the neutron experiments and Main ring accelerator. In case of such high intensity hadron accelerator, the most important issue is to reduce the uncontrolled loss. The beam collimation system is designed for this purpose. In the present design, the physical aperture is 1.5 times wider than the primary collimator aperture and the beam loss can be enough localized on this condition. After a startup of RCS in 2007, the collimator system of RCS worked well. But vacuum leakage occurred during the maintenance period in April, 2016. Since it was expected that the beam collimator was radio-activated very much, we took the influence of radiation into consideration and designed the collimator (ie. a remote clamp system to connect/take off it with a vacuum flange away from itself). Therefore, during the recovery work of the collimator, we were able to reduce the worker dose to less than 60 micro Sv though the collimator block had a residual dose of 40 mSv/h.

Journal Articles

Signal response of the beam loss monitor as a function of the lost beam energy

Yamamoto, Kazami

Proceedings of 4th International Beam Instrumentation Conference (IBIC 2015) (Internet), p.80 - 84, 2016/02

The 3 GeV rapid cycling synchrotron of the J-PARC accelerates a proton beam up to 3 GeV and delivers it to the main ring and the material and life science facility. The main magnets (dipole and quadrupole magnets) of the synchrotron have large aperture, and thickness of yoke is larger than 200 mm. Considering the stopping power of a proton, a shielding effect of the magnets for beam loss monitor strongly depends on the lost beam energy. When the beam loss occurs during injection, the lost proton cannot penetrate the magnet yoke. But when the beam loss occurs after acceleration, lost beam easily pass the magnet. Therefore the signal response of the beam loss monitor is changed by the lost energy. We estimated the signal dependence on the lost energy by the simulation. The results indicated that the response strongly depends on the location of the lost point and lost energy. It is proportional to the lost power except the condition that the magnets become the radiation shielding.

JAEA Reports

Study of technical issues on proton beam line tunnel in material/life science experimental facility of high intensity proton accelerator project

Sakamoto, Shinichi; Meigo, Shinichiro; Konno, Chikara; Harada, Masahide; Miyake, Yasuhiro*; Kasugai, Yoshimi; Muto, Suguru*; Fujimori, Satoru*; Ono, Takehiro; Ikeda, Yujiro

JAERI-Tech 2001-075, 168 Pages, 2001/12

JAERI-Tech-2001-075.pdf:12.78MB

no abstracts in English

Journal Articles

Concept of staged approach for international fusion materials irradiation facility

Sugimoto, Masayoshi; Kinsho, Michikazu; Takeuchi, Hiroshi

Proceedings of 20th International Linac Conference, p.651 - 653, 2000/00

no abstracts in English

Journal Articles

Precise beam simulation of high current linac for IFMIF

Sugimoto, Masayoshi

Proc. of 2nd Int. Topical Meeting on Nuclear Applications of Accelerator Technology (AccApp'98), p.566 - 571, 1998/00

no abstracts in English

Journal Articles

A Beam simulation of the proton storage ring for the neutron science project

Noda, Fumiaki*; Kinsho, Michikazu; Kusano, Joichi; Mizumoto, Motoharu

Proc. of 11th Symp. on Accelerator Sci. and Technol., p.350 - 352, 1997/00

no abstracts in English

JAEA Reports

Vacuum system for JAERI AVF cyclotron

Nakamura, Yoshiteru; Ishibori, Ikuo; Okumura, Susumu; Nara, Takayuki; Yokota, Wataru; Fukuda, Mitsuhiro; Agematsu, Takashi; Arakawa, Kazuo; Mizuhashi, Kiyoshi; Sano, M.*; et al.

JAERI-M 94-007, 74 Pages, 1994/02

JAERI-M-94-007.pdf:2.99MB

no abstracts in English

Oral presentation

Localization of the beam loss caused by the foil scattering for high-intensity routine operation in the J-PARC 3-GeV Rapid Cycling Synchrotron

Kato, Shinichi; Yamamoto, Kazami; Harada, Hiroyuki; Hotchi, Hideaki; Kinsho, Michikazu

no journal, , 

The J-PARC 3-GeV rapid cycling synchrotron (RCS) accelerates proton beams from 400 MeV to 3 GeV and the designed output beam power is 1 MW. To achieve a high-intensity output beam power, the RCS adapts H$$^{-}$$ charge-exchange multi-turn injection. The H$$^{-}$$ beam from the Linac is delivered to the RCS injection point, where it is injected through a carbon stripper foil in order to strip two electrons and to convert into proton. This injection is divided into 308 turns. Therefore, the both injection and circulating beams hit the foil repeatedly and scattering occur during the injection. Especially, large-scattered particles cause uncontrolled beam losses at downstream area. Thus, a new collimation system was developed and installed downstream of the foil to localize these losses in 2011. In the beam commissioning at 181 MeV and 400 MeV injection energy, unique tuning method of the collimator has been established and consequently these uncontrolled beam losses were localized successfully.

Oral presentation

Measurement of residual dose distribution and activation due to beam losses in J-PARC RCS

Yoshimoto, Masahiro; Takeda, Osamu; Harada, Hiroyuki; Yamamoto, Kazami; Kinsho, Michikazu

no journal, , 

Suppression of device radiations due to beam losses in the high intensity proton accelerators is one of the key issues to achieve MW class high power beam operation. In the J-PARC RCS, Ring collimator system which can localize the beam loss in the ring is adopted to suppress the device radiations. However, high residual doses are observed around the stripper foil. During the multi-turn charge exchange beam injection, not only the injecting beam but also circulating beam hit the foil, and then a large number of secondary particles, namely protons and neutrons, are generated. PHITS simulation results indicate that the secondary particles cause the high residual doses around the foil. Thus, we developed a new BLM which can detect the beam loss at the localized spot area. This new BLM can relate the beam loss with the radio activation of the device at the spot area. Detected radiations by this new BLM are occurred during the beam injection period and the total amount of the signal is directly proportional to the frequency of both the injecting and the circulating beam irradiation. Beam loss evaluation method combining the detailed residual dose survey by the GM counter after the beam stop into the radiations measurement by the BLM during the beam operation is effectively to reveal the beam losses structure from the point of view of the beam dynamics in the accelerator. In this presentation, we report the relation between the BLM signals and residual doses, and the beam losses structure and the mechanism.

Oral presentation

Interlocked events analysis based on beam instrumentation data at J-PARC Linac and RCS

Hayashi, Naoki

no journal, , 

In order to realize stable accelerator operation, it is necessary to understand various interlocked events and take countermeasures. In the J-PARC Linac, many interlocked events which include waveform data of current monitors and beam loss monitors, were recorded and classified to the various pattern. Their counter measures are under consideration. In the RCS (Rapid-Cycling Synchrotron), new processing unit is prepared to record beam current and position date of interlocked event and its future perspective will be reported.

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