Electromagnetic design of the low beta cavities for the JAEA ADS

Yee-Rendon, B.; Kondo, Yasuhiro; Maekawa, Fujio; Meigo, Shinichiro; Tamura, Jun

Journal of Physics; Conference Series, 1350(1), p.012197_1 - 012197_7, 2019/12

https://iopscience.iop.org/article/10.1088/1742-6596/1350/1/012197

Evaluation of 2-D transverse beam profile monitor using gas sheet at J-PARC LINAC

Kamiya, Junichiro; Okabe, Kota; Kinsho, Michikazu; Moriya, Katsuhiro; Yamada, Ippei; Ogiwara, Norio*; Hikichi, Yusuke*; Wada, K.*

Journal of Physics; Conference Series, 1350, p.012149_1 - 012149_6, 2019/12

https://doi.org/10.1088/1742-6596/1350/1/012149

To obtain a getter effect to titanium vacuum duct surface, the method to remove the oxide on the surface by sputtering with ionized molecules has been developed. In the method, a sheet-shaped gas distribution with a uniform and high density is generated through a narrow slit by a small amount of gas. In this report, the gas density distribution was calculated by the Monte Carlo simulation code. As a result, it was found that a gas injection from both directions was effective to generate uniform density distribution. Furthermore, the gas injection method was applied to a non-destructive beam profile monitor, that detects ions generated by the interaction between gas molecules and beam. In this monitor, dependence of the beam profile on the injected gas amount was measured. A small amount of injected gas was found to be ideal for the beam profile measurements in the unsaturated and a high S/N ratio region.

Simulations of beam loading compensation in a wideband accelerating cavity using a circuit simulator including a LLRF feedback control

Tamura, Fumihiko; Yamamoto, Masanobu; Sugiyama, Yasuyuki*; Yoshii, Masahito*; Omori, Chihiro*; Shimada, Taihei; Nomura, Masahiro; Hasegawa, Katsushi*; Hara, Keigo*; Furusawa, Masashi*

Journal of Physics; Conference Series, 1350(1), p.012189_1 - 012189_7, 2019/12

https://doi.org/10.1088/1742-6596/1350/1/012189

Magnetic alloy cavities are employed in the J-PARC RCS to generate high accelerating voltages. The cavity, which is driven by a vacuum tube amplifier, has a wideband frequency response and the beam loading in the cavity is multiharmonic. Therefore, the tube must generate a multiharmonic output current. An LTspice circuit model is developed to analyze the vacuum tube operation and the compensation of the multiharmonic beam loading. The model includes the cavity, tube amplifier, beam current, and LLRF feedback control. The feedback control consists of the I/Q demodulator including low pass filters, PI control, and I/Q modulator. In this presentation, we present the implementation of the LLRF functions in the LTspice simulations. The preliminary simulation results are also presented. The simulations fairly agree with the beam test results.

Longitudinal measurements and beam tuning in the J-PARC linac MEBT1

Otani, Masashi*; Futatsukawa, Kenta*; Miyao, Tomoaki*; Liu, Y.*; Hirano, Koichiro; Kondo, Yasuhiro; Miura, Akihiko; Oguri, Hidetomo

Journal of Physics; Conference Series, 1350, p.012078_1 - 012078_5, 2019/12

https://doi.org/10.1088/1742-6596/1350/1/012078

The Japan Proton Accelerator Research Complex (J-PARC) linac is operated with design peak current of 50 mA from 2018. For operation with such a high beam current, itis important to understand transverse and longitudinal beam properties especially in low-velocity region. A medium energy beam transport (MEBT1) line between the 3-MeV radio-frequency quadrupole linac (RFQ) and the 50-MeV drift-tube linac (DTL) is a 3-m-long transport line to match the beam to the DTL and produce a macro pulse configuration for a 3-GeV rapid-cycling synchrotron (RCS). In this paper, recent measurements and beam tuning results in MEBT1 will be presented.

Negative muonium ion production with a C12A7 electride film

Otani, Masashi*; Fukao, Yoshinori*; Futatsukawa, Kenta*; Kawamura, Naritoshi*; Matoba, Shiro*; Mibe, Tsutomu*; Miyake, Yasuhiro*; Shimomura, Koichiro*; Yamazaki, Takayuki*; Hasegawa, Kazuo; et al.

Journal of Physics; Conference Series, 1350, p.012067_1 - 012067_6, 2019/12

https://doi.org/10.1088/1742-6596/1350/1/012067

Negative muonium atom (ee, Mu) has unique features stimulating potential interesting for several scientific fields. Since its discovery in late 1980's in vacuum, it has been discussed that the production efficiency would be improved using a low-work function material. C12A7 was a well-known insulator as a constituent of alumina cement, but was recently confirmed to exhibit electric conductivity by electron doping. The C12A7 electride has relatively low-work function (2.9 eV). In this paper, the negative muonium production measurement with several materials including a C12A7 electride film will be presented. Measured production rate of the Mu were 10/s for all the Al, electride, and SUS target. Significant enhancement on electride target was not observed, thus it is presumed that the surface condition should be more carefully treated. There was no material dependence of the Mu averaged energy: it was 0.20.1keV.

The First replacement of the RF window of the ACS cavity

Tamura, Jun; Kondo, Yasuhiro; Morishita, Takatoshi; Naito, Fujio*; Otani, Masashi*; Nemoto, Yasuo*

Journal of Physics; Conference Series, 1350, p.012079_1 - 012079_6, 2019/12

https://doi.org/10.1088/1742-6596/1350/1/012079

In 2013, the Annular-ring Coupled Structure (ACS) cavities were installed to the Japan Proton Accelerator Research Complex (J-PARC) linac. Since then, the ACS cavities have been stably running. Although any serious problem induced by the RF window had not yet observed, we decided to replace the RF window of one ACS cavity by the newly manufactured one. The major motivations of the replacement are to check the surface condition of the RF window which have been under operation for nearly five years, to confirm that the new RF window fully meets specifications, and to learn how much time is required for high-power conditioning of the new RF window. By making use of the summer maintenance period of 2018, we carried out the replacement. This was the first experience for us to replace the RF window installed to the ACS cavity in the linac accelerator tunnel. As for the removed RF window, there was no any abnormal warning found with the visual examination. At the resuming of the cavity operation after the maintenance period, we conducted the high-power conditioning in a measured manner. It took around fifty hours so that the targeted peak power was stably input to the cavity through the new RF window. The ACS cavity with the new RF window is now stably operating.

New design of vacuum chambers for radiation shield installation at beam injection area of J-PARC RCS

Kamiya, Junichiro; Kotoku, Hirofumi; Shobuda, Yoshihiro; Takayanagi, Tomohiro; Yamamoto, Kazami; Yanagibashi, Toru*; Horino, Koki*; Miki, Nobuharu*

Journal of Physics; Conference Series, 1350, p.012172_1 - 012172_7, 2019/12

https://doi.org/10.1088/1742-6596/1350/1/012172

One of the issues in the J-PARC 3 GeV rapid cycling synchrotron is the high residual radiation dose around the beam injection point. A radiation shield is necessary to reduce radiation exposure of workers when maintenance is performed there. A space to install the radiation shield should be secured by newly designing a structure of the vacuum chamber at the injection point and the alumina ceramics beam pipes for the shift bump magnets. To make the space for the shield, the chamber is lengthened along the beam line and the cross-sectional shape is changed from circle to rectangle. The displacement and inner stress of the vacuum chamber due to atmospheric pressure were evaluated to be enough small by the calculation. For the ceramics beam pipe's rf-shield, the damping resistor was effective to reduce the induced modulation voltages by the pulsed magnetic field.

Development of a beam window protection system for the J-PARC Linac

Takahashi, Hiroki; Hatakeyama, Shuichiro; Sawabe, Yuki; Miyao, Tomoaki*; Ishiyama, Tatsuya*; Suzuki, Takahiro*

Journal of Physics; Conference Series, 1350, p.012142_1 - 012142_5, 2019/12

https://doi.org/10.1088/1742-6596/1350/1/012142

At the J-PARC Linac, beam conditioning and study are performed using beam dumps (BDs). To be a partition with the high vacuum section, a beam window (material Ni, 0.38 mm thick, mirror-shape) is installed upstream of the BD along the beam line. Beams that can be accepted by the beam window are about 1/50 or less of rated beam according to thermal evaluation and experience. Therefore, when using a beam dump, it is necessary not to exceed this tolerance. In a 2018 beam study, the beam e that exceeded tolerance was incident on the 0-degree dump due to human error, and the beam window was cracked. Then, this has revealed the need for protection of the beam window by hardware. Therefore, based on the existing system for monitoring the per-hour beam amount, we began to develop a system to monitor one shot beam and one second beam amount. And, we succeeded in implementing a system that protects the beam window by monitoring the beam in a short time (one shot, and for one second). In addition, the performance tests using actual beams were performed, and it was confirmed that the developed system had sufficient performance requirements to protect the beam window.

Energy measurement and correction for stable operation in J-PARC

Moriya, Katsuhiro; Harada, Hiroyuki; Liu, Y.*; Otani, Masashi*

Journal of Physics; Conference Series, 1350, p.012140_1 - 012140_5, 2019/11

https://doi.org/10.1088/1742-6596/1350/1/012140

Charmed dibaryon resonances in the potential quark model

Oka, Makoto; Maeda, Saori*; Liu, Y.-R.*

International Journal of Modern Physics; Conference Series (Internet), 49, p.1960004_1 - 1960004_8, 2019/07

https://doi.org/10.1142/S2010194519600048

The charmed dibaryon resonances are given by a model Hamiltonian with the quark-model based short-range interaction and the long-range meson-exchange interactions. Sharp resonances states below the - and - thresholds are predicted.