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Journal Articles

Chiral Dirac fermion in a collinear antiferromagnet

Zhang, A.*; Deng, K.*; Sheng, J.*; Liu, P.*; Kumar, S.*; Shimada, Kenya*; Jiang, Z.*; Liu, Z.*; Shen, D.*; Li, J.*; et al.

Chinese Physics Letters, 40(12), p.126101_1 - 126101_8, 2023/12

Journal Articles

Main outputs from the OECD/NEA ARC-F Project

Maruyama, Yu; Sugiyama, Tomoyuki*; Shimada, Asako; Lind, T.*; Bentaib, A.*; Sogalla, M.*; Pellegrini, M.*; Albright, L.*; Clayton, D.*

Proceedings of 20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-20) (Internet), p.4782 - 4795, 2023/08

Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Journal Articles

Dirac gap opening and Dirac-fermion-mediated magnetic coupling in antiferromagnetic Gd-doped topological insulators and their manipulation by synchrotron radiation

Shikin, A. M.*; Estyunin, D. A.*; Surnin, Yu. I.*; Koroleva, A. V.*; Shevchenko, E. V.*; Kokh, K. A.*; Tereshchenko, O. E.*; Kumar, S.*; Schwier, E. F.*; Shimada, Kenya*; et al.

Scientific Reports (Internet), 9(1), p.4813_1 - 4813_17, 2019/03

 Times Cited Count:19 Percentile:71.98(Multidisciplinary Sciences)

Journal Articles

Vacuum tube operation analysis under multi-harmonic driving and heavy beam loading effect in J-PARC RCS

Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*; Schnase, A.*

Nuclear Instruments and Methods in Physics Research A, 835, p.119 - 135, 2016/11

 Times Cited Count:5 Percentile:49.65(Instruments & Instrumentation)

A magnetic alloy loaded cavity is used to generate multi-harmonic rf voltage in J-PARC RCS. However, a vacuum tube operation analysis under the multi-harmonic driving is very complicated because many variables should be solved with a self consistency. At the conventional operation analysis, a hand work by tracing the constant current curve of the tube was performed, or an appropriate single harmonic wave form was assumed. We have developed a numerical analysis code which calculates the vacuum tube operation automatically and it realizes the multi-harmonic vacuum tube operation analysis. The code is verified at the high power beam acceleration test and we confirm the calculation results are consistent with the measurement ones. We can calculate the vacuum tube operation precisely by using the code, and it will contribute to improving the quality of the beam in the high intensity proton synchrotron.

Journal Articles

Reference design of the power supply system for the resistive-wall-mode control in JT-60SA

Ferro, A.*; Gaio, E.*; Novello, L.*; Matsukawa, Makoto; Shimada, Katsuhiro; Kawamata, Yoichi; Takechi, Manabu

Fusion Engineering and Design, 98-99, p.1053 - 1057, 2015/10

 Times Cited Count:2 Percentile:26.04(Nuclear Science & Technology)

Journal Articles

First switching network unit for the JT-60SA superconducting central solenoid

Lampasi, A.*; Zito, P.*; Coletti, A.*; Novello, L.*; Matsukawa, Makoto; Shimada, Katsuhiro; Burini, F.*; Kuate-Fone, Y.*; Taddia, G.*; Tenconi, S.*

Fusion Engineering and Design, 98-99, p.1098 - 1102, 2015/10

 Times Cited Count:9 Percentile:61(Nuclear Science & Technology)

Journal Articles

Design and realization of JT60-SA Fast Plasma Position Control Coils power supplies

Zito, P.*; Lampasi, A.*; Coletti, A.*; Novello, L.*; Matsukawa, Makoto; Shimada, Katsuhiro; Cinarelli, D.*; Portesine, M.*; Dorronsoro, A.*; Vian, D.*

Fusion Engineering and Design, 98-99, p.1191 - 1196, 2015/10

 Times Cited Count:13 Percentile:73.52(Nuclear Science & Technology)

Journal Articles

Overview of the new magnet power supply systems of JT-60SA procured by EU

Novello, L.*; Baulaigue, O.*; Coletti, A.*; Dumas, N.*; Ferro, A.*; Gaio, E.*; Lampasi, A.*; Maistrello, A.*; Matsukawa, Makoto; Shimada, Katsuhiro; et al.

Fusion Engineering and Design, 98-99, p.1122 - 1126, 2015/10

 Times Cited Count:16 Percentile:79.67(Nuclear Science & Technology)

Journal Articles

Simulation of phase modulation for longitudinal emittance blow-up in J-PARC MR

Yamamoto, Masanobu; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Nomura, Masahiro; Omori, Chihiro*; Schnase, A.*; Shimada, Taihei; Takagi, Akira*; Takata, Koji*; et al.

JPS Conference Proceedings (Internet), 8, p.012015_1 - 012015_6, 2015/09

The J-PARC MR provides a coasting proton beam for nuclear physics experiments by slow extraction. The longitudinal emittance should be enlarged until the MR flat top to mitigate the microwave instability. We have investigated a Phase Modulation (PM) method by using a High Frequency Cavity (HFC) to increase the emittance. We have performed extensive simulation studies to find the appropriate parameters of the PM through the particle tracking simulation. We found that the effective HFC frequency has linear dependence with the PM frequency, where the emittance is smoothly enlarged. Furthermore, we found that the required HFC voltage is inverse proportional to the square root of the duration time of the PM. These PM properties will be used for the design of the HFC. We describe the particle tracking simulation results of controlled emittance blow-up by the PM.

Journal Articles

High intensity single bunch operation with heavy periodic transient beam loading in wide band RF cavities

Tamura, Fumihiko; Hotchi, Hideaki; Schnase, A.*; Yoshii, Masahito*; Yamamoto, Masanobu; Omori, Chihiro*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hasegawa, Katsushi*; et al.

Physical Review Special Topics; Accelerators and Beams, 18(9), p.091004_1 - 091004_8, 2015/09

 Times Cited Count:4 Percentile:30.88(Physics, Nuclear)

The RCS in the J-PARC was originally designed to accelerate two high intensity bunches, while some of neutron experiments in the MLF and a muon experiment using MR beams require a single bunch operation mode. The beam intensity in the single bunch operation has been limited by longitudinal beam losses due to the rf bucket distortions by the wake voltage of the odd harmonics in the wide band MA cavities. We installed an additional rf feedforward system to compensate the wake voltages of the odd harmonics (h=1,3,5). The longitudinal beam losses during the single bunch acceleration disappeared with feedforward for the odd harmonics. We also confirmed that the beam quality in the single bunch acceleration are similar to that of the normal operation with two bunches. Thus, high intensity single bunch acceleration at the intensity of 2.3$$times$$10$$^{13}$$ protons per bunch has been achieved in the J-PARC RCS.

Journal Articles

Type tests of JT-60SA Fast Plasma Position Control Coil (FPPCC) power supplies

Zito, P.*; Lampasi, A.*; Novello, L.*; Matsukawa, Makoto; Shimada, Katsuhiro; Portesine, M.*; Fasce, F.*; Cinarelli, D.*; Dorronsoro, A.*; Vian, D.*

Proceedings of IEEE 15th International Conference on Environment and Electrical Engineering (IEEE-EEEIC 2015), p.156 - 160, 2015/06

Journal Articles

Design and implementation of four 20 kA, 5 kV hybrid switching networks for plasma ignition in the international tokamak JT-60SA

Burini, F.*; Kuate-Fone, Y.*; Taddia, G.*; Tenconi, S.*; Lampasi, A.*; Zito, P.*; Matsukawa, Makoto; Shimada, Katsuhiro; Coletti, A.*; Novello, L.*

Proceedings of 40th Annual Conference of the IEEE Industrial Electronics Society (IECON 2014), p.5035 - 5040, 2014/10

Journal Articles

Ribbon thickness dependence of the magnetic alloy core characteristics in the accelerating frequency region of the J-PARC synchrotrons

Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Takata, Koji*; Toda, Makoto*; Yoshii, Masahito*; et al.

Nuclear Instruments and Methods in Physics Research A, 749, p.84 - 89, 2014/06

 Times Cited Count:2 Percentile:19.31(Instruments & Instrumentation)

We have been developing high shunt impedance Magnetic Alloy (MA) cores. The MA core shunt impedance is a key parameter to achieve a higher field gradient for increasing a beam power. We increase the MA core shunt impedance by two different ways. One way is applying an external magnetic field during annealing to increase the MA core magnetic properties. The other way is using thinner ribbons to reduce the eddy current. In this paper, we discuss the latter way.

Journal Articles

Study of high impedance magnetic alloy core

Nomura, Masahiro; Yamamoto, Masanobu; Shimada, Taihei; Tamura, Fumihiko; Omori, Chihiro*; Toda, Makoto*; Hasegawa, Katsushi*; Hara, Keigo*; Yoshii, Masahito*; Schnase, A.*

Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.217 - 220, 2014/06

J-PARC RCS and MR employ RF cavities loaded with Magnetic Alloy (MA) cores. To achieve the high shunt impedance, we measured the shunt impedance with changing the core filling factor, ribbon thickness, and magnetization process. The shunt impedance was reduced in despite of the filling factor increase because the strong winding tension deteriorate the magnetic property. The MA core with thin ribbons and the MA core that is magnetized by a rotation process show high permeability in the accelerating frequency region, and those MA cores show the high shunt impedance consequently.

Journal Articles

Various usages of wall current monitors for commissioning of RF systems in J-PARC synchrotrons

Tamura, Fumihiko; Yamamoto, Masanobu; Schnase, A.; Yoshii, Masahito*; Omori, Chihiro*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hara, Keigo*; Hasegawa, Katsushi*

Proceedings of 1st International Beam Instrumentation Conference (IBIC 2012) (Internet), p.63 - 65, 2013/06

Wall current monitors (WCM) for RF system commissioning are installed in the J-PARC synchrotrons, the RCS and the MR. The WCM signals are used for diagnosis to adjust the RF system parameters. For the diagnosis, the WCM signals are taken by an oscilloscope with the revolution clock signal generated by the LLRF control system, and slices of the WCM waveform with lengths of the revolution periods are generated. By stacking the slices, one can get a mountain plot, which shows motions of bunches and variations of the bunch shapes. Also, time variations of the bunching factor, which are important for acceleration of high intensity proton beams, are obtained. The harmonic analysis is performed on the WCM signal and the cavity voltage monitor signal. By using complex amplitudes of them, one can calculate the impedance seen by the beam. The RF parameters for high intensity beams have been successfully adjusted by using these analyses.

Journal Articles

Inner diameter change over the years of MA cores of RF-cavities at the J-PARC 3 GeV synchrotron

Shimada, Taihei; Nomura, Masahiro; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*; Schnase, A.*; et al.

Proceedings of 4th International Particle Accelerator Conference (IPAC '13) (Internet), p.2750 - 2752, 2013/06

no abstracts in English

Journal Articles

Commissioning of beam loading compensation system in the J-PARC MR

Tamura, Fumihiko; Omori, Chihiro*; Yamamoto, Masanobu; Yoshii, Masahito*; Schnase, A.*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hasegawa, Katsushi*; Hara, Keigo*

Proceedings of 4th International Particle Accelerator Conference (IPAC '13) (Internet), p.2540 - 2542, 2013/06

Beam loading compensation is indispensable to accelerate high intensity proton beams in the J-PARC MR. The MA-loaded rf cavities in the MR are driven by the single harmonic (h = 9) rf signals, while the cavity frequency response covers also the neighbor harmonics (h = 8, 10). The wake voltage induced by the beam consists of the three harmonics (h = 8, 9, 10). We employ the rf feedforward method to compensate the beam loading of these harmonics. The full-digital feedforward system was developed for the MR. We have successfully commissioned the feedforward patterns for all of eight cavities by using high intensity beams with 1.0$$times$$10$$^{14}$$ ppp. We present the commissioning results. The impedance seen by the beam is reduced and the longitudinal oscillations due to the beam loading are reduced. By the beam loading compensation, high power beam operation at the beam power of 200 kW has been achieved.

Journal Articles

Influence of core winding tension and ribbon quality on the MA core RF characteristics

Nomura, Masahiro; Schnase, A.*; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*

Proceedings of 4th International Particle Accelerator Conference (IPAC '13) (Internet), p.2747 - 2749, 2013/06

During the development of Magnetic Alloy (MA) cores for RF cavities, the core shunt impedance was increased by lowering a core winding tension to improve the electrical insulation between MA ribbon layers. The lower winding tension reduced the core filling factor. The core shunt impedance might be reduced according to the core filling factor reduction. We study the influence of improving the electrical insulation and lowering the core winding tension on the core shunt impedance.

Journal Articles

Multiharmonic RF feedforward system for compensation of beam loading and periodic transient effects in magnetic-alloy cavities of a proton synchrotron

Tamura, Fumihiko; Omori, Chihiro*; Yamamoto, Masanobu; Yoshii, Masahito*; Schnase, A.*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hasegawa, Katsushi*; Hara, Keigo*

Physical Review Special Topics; Accelerators and Beams, 16(5), p.051002_1 - 051002_12, 2013/05

 Times Cited Count:5 Percentile:38.74(Physics, Nuclear)

Beam loading compensation is a key for acceleration of a high intensity proton beam in the MR of J-PARC. Magnetic alloy loaded rf cavities with a Q value of 22 are used to achieve high accelerating voltages. The cavity is driven by a single harmonic (h = 9) rf signal while the cavity frequency response also covers the neighbor harmonics (h = 8, 10). Therefore the wake voltage induced by the high intensity beam consists of the three harmonics, h = 8, 9, 10. We employ the rf feedforward method to compensate the beam loading ofthese three harmonics (h = 8, 9, 10). The full-digital multiharmonic feedforward system was developed for the MR. The commissioning of the feedforward system has been performed by using high intensity beams with 1.0$$times$$10$$^{14}$$ protons per pulse. The longitudinal oscillations due to the beam loading are reduced. By the beam loading compensation, stable high power beam operation is achieved.

103 (Records 1-20 displayed on this page)