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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 instruments for high power spallation neutron source and facility for ADS

Meigo, Shinichiro

Proceedings of 61st ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams (HB 2018) (Internet), p.99 - 103, 2018/07

As the increase of beam power, beam instruments play an essential role in the Hadron accelerator facility. In J-PARC, the pitting erosion on the mercury target vessel for the spallation neutron source is one of a pivotal issue to operate with the high power of the beam operation. Since the erosion is proportional to the 4th power of the beam current density, the minimization of the peak current density is required. To achieve low current density, the beam-flattening system by nonlinear beam optics in J-PARC, by which the peak density was successfully reduced by 30% than the density with the conventional case optics. Since the ADS requires a very powerful accelerator with the beam power such as 30 MW, a robust beam profile monitor is required, especially for the observation of the beam status on the target continuously. A candidate material for the beam monitor was developed by using heavy-ion of Ar beam to give the damage efficiently.

Journal Articles

Research and development of high intensity beam transport to the target facilities at J-PARC

Meigo, Shinichiro; Oi, Motoki; Ikezaki, Kiyomi*; Kawasaki, Tomoyuki; Kinoshita, Hidetaka; Akutsu, Atsushi*; Nishikawa, Masaaki*; Fukuda, Shimpei

Proceedings of 12th International Topical Meeting on Nuclear Applications of Accelerators (AccApp '15), p.255 - 260, 2016/00

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