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Toyama, Takeshi*; Tanno, Takashi; Yano, Yasuhide; Inoue, Koji*; Nagai, Yasuyoshi*; Otsuka, Satoshi; Miyazawa, Takeshi; Mitsuhara, Masatoshi*; Nakashima, Hideharu*; Onuma, Masato*; et al.
Journal of Nuclear Materials, 599, p.155252_1 - 155252_14, 2024/10
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)We investigated the stability of oxide nano particles in oxide dispersion-strengthened (ODS) steel, which is a promising candidate material for next-generation reactors, under neutron irradiation at high temperature to high doses. MA957, a 14Cr-ODS steel, was irradiated with Joyo in Japan Atomic Energy Agency under irradiation conditions of 130 dpa at 502
C, 154 dpa at 589C, and 158 dpa at 709C. Three-dimensional atom probe (3D-AP) and transmission electron microscope (TEM) observation were performed to characterize the oxide particles in the ODS steels. A high number density of Y-Ti-O particle was observed in the unirradiated and irradiated samples. Almost no change in the morphology of the oxide particles, i.e. average diameter, number density, and chemical composition, has been observed in the samples irradiated to 130 dpa at 502C and to 154 dpa at 589C. A slight decrease in number density was observed in the sample irradiated to 158 dpa at 709CC. The hardness of any of the irradiated samples was almost unchanged from that of the unirradiated sample. It was revealed that the oxide particles existed stable, and the strength of the material was sufficiently maintained even after being neutron irradiated to high dose of 
160 dpa at high temperature up to 700C. A part of this study includes the results of MEXT Innovative Nuclear Research and Development Program Grant Number JPMXD0219214482.
C to 1000CImagawa, Yuya; Hashidate, Ryuta; Miyazawa, Takeshi; Onizawa, Takashi; Otsuka, Satoshi; Yano, Yasuhide; Tanno, Takashi; Kaito, Takeji; Onuma, Masato*; Mitsuhara, Masatoshi*; et al.
Journal of Nuclear Science and Technology, 61(6), p.762 - 777, 2024/06
Times Cited Count：3 Percentile：51.90(Nuclear Science & Technology)The Japan Atomic Energy Agency has been developing 9Cr-oxide dispersion strengthened (ODS) steel as a fuel cladding material for sodium-cooled fast reactors (SFRs). Previous studies have formulated the creep rupture equation for 650C to 850C. However, little data have been obtained above 850C, and no equation has been formulated. This study conducted creep tests to evaluate creep strength at 700C to 1000C. Two creep test methods, the internal pressure and ring creep tests under development, were used, and the validation of the ring creep test method was conducted. The results showed that 9Cr-ODS steel undergoes almost no strength change due to the matrix's phase transformation, and a single equation can express a creep rupture strength from 700C to 1000C. In validating the ring creep test method, analysis clarified the effect of stress concentration on the specimen. Plastic deformation occurs at high initial stress and may lead to early rupture. The results will be essential for future creep testing and evaluation of neutron-irradiated 9Cr-ODS steel.
Miyazawa, Takeshi; Tanno, Takashi; Imagawa, Yuya; Hashidate, Ryuta; Yano, Yasuhide; Kaito, Takeji; Otsuka, Satoshi; Mitsuhara, Masatoshi*; Toyama, Takeshi*; Onuma, Masato*; et al.
Journal of Nuclear Materials, 593, p.155008_1 - 155008_16, 2024/05
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Yoshimura, Nobuyuki*; Toyama, Takeshi*; Shobuda, Yoshihiro; Nakamura, Takeshi*; Omi, Kazuhito*; Kobayashi, Aine*; Okada, Masashi*; Sato, Yoichi*; Nakaya, Tsuyoshi*
Proceedings of 20th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.260 - 264, 2023/11
The J-PARC main ring (MR) will be increased to 1.3 MW. To cope with the increase in beam intensity, the intra-bunch feedback system (IBFB) needs to be upgraded to handle higher frequencies up to about 200 MHz. To evaluate the performance and understand the optimal parameters after this upgrade, we are developing a particle tracking simulation that includes the necessary components. The recoherence period induced by chromaticity between tracking simulations and experiments are compared and it cannot be discribed by the simple simulations, and we investigate what mechanisms explain this result. The shift of synchrotron tune caused by longitudinal wakes using tracking simulations are calculated and it find that introducing the effect of longitudinal wakes only does not explain the recoherence period in the experimental results.
Yoshida, Kenta*; Toyama, Takeshi*; Inoue, Koji*; Nagai, Yasuyoshi*; Shimodaira, Masaki
Materia, 62(3), p.154 - 158, 2023/03
no abstracts in English
Mitsuhara, Masatoshi*; Kurino, Koichi*; Yano, Yasuhide; Otsuka, Satoshi; Toyama, Takeshi*; Onuma, Masato*; Nakashima, Hideharu*
Tetsu To Hagane, 109(3), p.189 - 200, 2023/03
Times Cited Count：1 Percentile：14.99(Metallurgy & Metallurgical Engineering)Oxide Dispersion Strengthened (ODS) ferritic steel, a candidate material for fast reactor fuel cladding, has low thermal expansion, good thermal conductivity, and excellent resistance to irradiation damage and high temperature strength. The origin of the excellent high-temperature strength lies in the dispersion of fine oxides. In this study, creep tests at 700 or 750C, which are close to the operating temperatures of fast reactors, and high-temperature tensile tests at 900 to 1350 C, which simulate accident conditions, were conducted on 9Cr ODS ferritic steels, M11 and MP23, and 12Cr ODS ferritic steel, F14, to confirm the growth behavior of oxides. In the M11 and F14 creep test samples, there was little oxide growth or decrease in number density from the initial state, indicating that dispersion strengthening by oxides was effective during deformation. After creep deformation of F14, the development of dislocation substructures such as dislocation walls and subgrain boundaries was hardly observed, and mobile dislocations were homogeneously distributed in the grains. The dislocation density increased with increasing stress during the creep test. In the high-temperature ring tensile tests of MP23 and F14, the strength of both steels decreased at higher temperatures. In MP23, elongation decreased with increasing test temperature from 900 to 1100 C, but increased at 1200 C, decreased drastically at 1250 C, and increased again at 1300 C. In F14, elongation decreased with increasing temperature. It was inferred that the formation of the 
-ferrite phase was responsible for this complex change in mechanical properties of MP23 from 1200 to 1300 C.
Tamura, Fumihiko; Omori, Chihiro*; Yoshii, Masahito*; Tomizawa, Masahito*; Toyama, Takeshi*; Sugiyama, Yasuyuki*; Hasegawa, Katsushi*; Kobayashi, Aine*; Okita, Hidefumi
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.175 - 178, 2023/01
J-PARC MR delivers high intensity proton beams to the neutrino experiment. Eight bunches with high peak currents are extracted from the MR by the extraction kicker, therefore the neutrino beam has the similar structure. Intermediate Water Cherenkov Detector (IWCD) will be installed for the future experiments and the IWCD requires a time structure with low peaks. We consider bunch manipulation at flattop of the MR for reducing the peak current. It should be quickly done to avoid the significant loss of the beam power. The beam gap for the kicker rise time must be kept. We propose a non-adiabatic bunch manipulation using the multiharmonic rf voltage. The longitudinal impedance in the MR can affect the beam stability. The feasibility of the manipulation is discussed by using the longitudinal simulations.
Kobayashi, Aine*; Toyama, Takeshi*; Nakamura, Takeshi*; Shobuda, Yoshihiro; Ishii, Koji*; Tomizawa, Masahito*; Takeuchi, Yasunao*; Sato, Yoichi*
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.19 - 23, 2023/01
In the J-PARC main ring, density modulation due to longitudinal beam instability occurs during the debunching process of coasting beams. This leads to the generation of an electron cloud, which in turn causes transverse beam instabilities. The transverse beam instability causes beam loss and the electron cloud is assumed to cause vacuum degradation, both of which hinder the beam intensity enhancement, so it is essential to clarify the causes and countermeasures. In particular, the longitudinal impedance of several hundred MHz has been investigated as relevant, and measures to reduce the impedance of individual devices are underway. The Eddy-current type septum magnet, newly installed this year, was found to have a large impedance by simulation. Therefore, we are investigating a method to reduce the impedance by a flange loaded with SiC radio wave absorber, which can be applied to locations where there is no spatial margin to install a taper. In this report, we will discuss the characterization of SiC to be used in actual devices, impedance simulation reflecting the results of SiC evaluation, and evaluation of the effect of impedance countermeasures by impedance measurement using the wire method, and progress in evaluating the effect on the beam by beam simulation and beam study.
Yoshimura, Nobuyuki*; Toyama, Takeshi*; Kobayashi, Aine*; Nakamura, Takeshi*; Okada, Masashi*; Shobuda, Yoshihiro; Nakaya, Tsuyoshi*
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.936 - 941, 2023/01
no abstracts in English
Yamamoto, Kazami; Kinsho, Michikazu; Hayashi, Naoki; Saha, P. K.; Tamura, Fumihiko; Yamamoto, Masanobu; Tani, Norio; Takayanagi, Tomohiro; Kamiya, Junichiro; Shobuda, Yoshihiro; et al.
Journal of Nuclear Science and Technology, 59(9), p.1174 - 1205, 2022/09
Times Cited Count：7 Percentile：77.01(Nuclear Science & Technology)In the Japan Proton Accelerator Research Complex, the purpose of the 3 GeV rapid cycling synchrotron (RCS) is to accelerate a 1 MW, high-intensity proton beam. To achieve beam operation at a repetition rate of 25 Hz at high intensities, the RCS was elaborately designed. After starting the RCS operation, we carefully verified the validity of its design and made certain improvements to establish a reliable operation at higher power as possible. Consequently, we demonstrated beam operation at a high power, namely, 1 MW. We then summarized the design, actual performance, and improvements of the RCS to achieve a 1 MW beam.
Shobuda, Yoshihiro; Toyama, Takeshi*; Yoshimoto, Masahiro; Hatakeyama, Shuichiro
Proceedings of 13th International Particle Accelerator Conference (IPAC 22) (Internet), p.1663 - 1666, 2022/07
Ceramic breaks are used in synchrotrons for many purposes. For example, they are inserted between the Multi-Wire Profile Monitors (MWPMs) on the injection line at the rapid cycling synchrotron (RCS) in J-PARC to completely prevent the wall currents accompanying beams from affecting the MWPMs. On the other hand, from the viewpoint of suppressing beam impedances and the radiation fields from the ceramic breaks, it would be preferable that the inner surface of the ceramic break is coated with titanium nitride (TiN), or covered over capacitors. In this report, we measure the radiation fields from the ceramic break with and without capacitors as well as the beam profile and investigate the effect of the ceramic break on the measurements.
Kobayashi, Aine*; Toyama, Takeshi*; Nakamura, Takeshi*; Shobuda, Yoshihiro; Ishi, Koji*
Nuclear Instruments and Methods in Physics Research A, 1031, p.166515_1 - 166515_12, 2022/05
Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)The beam power of the main ring of the Japan Proton Accelerator Research Complex (J-PARC) is currently being increased. For high-power beam realization, it is essential to suppress the beam instability that limits the beam power and to estimate and enact countermeasures against the beam coupling impedance of individual devices. The fast-extraction (FX) septum magnet will be replaced with another magnet that copes with higher numbers of repetition cycles. Despite their different structures, both septa demonstrated a large impedance in estimates performed by the CST studio suite wake-field solver. The widely used taper impedance-reduction method would be effective but receives spatial constraints. By attaching a copper plate and SiC to the flange of the septum magnet, we could effectively reduce the impedance. The copper plate on the flange reduces the impedance below the cut-off frequency. Moreover, when SiC was loaded, the remaining impedance was three times lower than when using the copper plate alone. After applying this method to the new septum magnet, the maximum longitudinal impedance was reduced to 1% of the value without countermeasures, largely improving the beam stability condition. We also estimated the required thickness of SiC and the calorific value. This method saves space and is installed by simple attachment to the flange, regardless of the shape of the beam pipe. Therefore, it is also applicable to other devices.
Wang, J.*; Hatano, Yuji*; Toyama, Takeshi*; Suzudo, Tomoaki; Hinoki, Tatsuya*; Alimov, V. Kh.*; Schwarz-Selinger, T.*
Journal of Nuclear Materials, 559, p.153449_1 - 153449_7, 2022/02
Times Cited Count：3 Percentile：45.58(Materials Science, Multidisciplinary)To study the effect of the content of chromium (Cr) in the tungsten (W) matrix on the vacancy formation and retention of hydrogen isotopes, the samples of the W-0.3Cr alloy were irradiated with 6.4 MeV Fe ions in the temperature range of 523-1273 K. These displacement-damaged samples were exposed to D
gas at a temperature of 673 K. The addition of 0.3% Cr into the W matrix resulted in a significant decrease in the retention of deuterium compared to pure W after irradiation especially at high temperature. Positron lifetime for W-0.3Cr alloy irradiated at 1073 K was almost similar to that for non-irradiated one. These facts indicate the suppression of the formation of vacancy-type defects by 0.3% Cr addition.
Takamizawa, Hisashi; Hata, Kuniki; Nishiyama, Yutaka; Toyama, Takeshi*; Nagai, Yasuyoshi*
Journal of Nuclear Materials, 556, p.153203_1 - 153203_10, 2021/12
Times Cited Count：4 Percentile：42.67(Materials Science, Multidisciplinary)Solute clusters (SCs) formed in pressurized water reactor surveillance test specimens neutron-irradiated to a fluence of 1 
10
n/cm
were analyzed via atom probe tomography to understand the effect of silicon on solute clustering and irradiation embrittlement of reactor pressure vessel steels. In high-Cu bearing materials, Cu atoms were aggregated at the center of cluster surrounded by the Ni, Mn, and Si atoms like a core-shell structure. In low-Cu bearing materials, Ni, Mn, and Si atoms formed cluster and these solutes were not comprised core-shell structure in SCs. While the number of Cu atoms in clusters was decreased with decreasing nominal Cu content, the number of Si atoms had clearly increased. The cluster radius (
) and number density (
) decreased and increased, respectively, with increasing nominal Si content. The shift in the reference temperature for nil-ductility transition (
RT
) showed a good correlation with the square root of volume fraction (
) multiplied by r (
). This suggested that the dislocation cutting through the particles mechanism dominates the precipitation hardening responsible for irradiation embrittlement. The negative relation between the nominal Si content and RT indicated that increasing of nominal Si content reduces the degree of embrittlement.
Toyama, Takeshi*; Suzudo, Tomoaki; Nagai, Yasuyoshi*; 9 of others*
Journal of Nuclear Materials, 556, p.153176_1 - 153176_7, 2021/12
Times Cited Count：6 Percentile：58.63(Materials Science, Multidisciplinary)We performed a high-precision investigation of radiation-enhanced diffusion (RED) using electron irradiation and three-dimensional atom probe (3D-AP). Cu-Fe diffusion pairs were created using high-purity Fe and Cu as base materials, and irradiated by 2 MeV electron. Cu diffusion into the Fe matrix was observed at the atomic level using 3D-AP, and the diffusion coefficient was obtained directly using Fick's law. RED was clearly observed, and the ratio of diffusion under irradiation to thermal diffusion was enhanced at low temperature. RED was quantitatively evaluated using the reaction kinetics model, and the model which consider only vacancies gave a good agreement. This gave experimental clarification that RED was dominated by irradiation-induced vacancies. In addition, the direct experimental results on the effect of irradiation on the solubility limits of Cu in Fe was obtained; solubility limits under irradiation were found to be lower than those under thermal aging.
Kobayashi, Aine*; Toyama, Takeshi*; Nakamura, Takeshi*; Shobuda, Yoshihiro; Ishii, Koji*
Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.287 - 291, 2021/10
no abstracts in English
Toyama, Takeshi*; Kobayashi, Aine*; Shobuda, Yoshihiro
Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.666 - 669, 2021/10
no abstracts in English
Shobuda, Yoshihiro; Toyama, Takeshi*
Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.75 - 79, 2021/10
The beam impedance of a ceramic break with thin titanium nitride coating (TiN) consists of resistive wall term caused by TiN, radiation term, and capacitive term made by the ceramic itself in parallel. The entire wall current continues to run in TiN even when the skin depth is much larger than the chamber thickness, except for the extremely thin TiN. This characteristic is useful in developing a wall current monitor with an improved frequency response.
Zhao, C.*; Suzudo, Tomoaki; Toyama, Takeshi*; Nishitani, Shigeto*; Inoue, Koji*; Nagai, Yasuyoshi*
Materials Transactions, 62(7), p.929 - 934, 2021/07
Times Cited Count：3 Percentile：17.29(Materials Science, Multidisciplinary)We succeeded in measuring the diffusion coefficient of Cu in Fe in a low temperature range that had not been measured so far. Since the diffusion couple, which is a general method for measuring the diffusion coefficient, can be applied only at high temperature, atom probe tomography and Cu precipitation rate theory were used in this study. The estimated diffusion coefficient was found to be more reliable than that obtained in previous studies. Therefore, it is considered that the estimation by the atom probe provided higher accuracy. Furthermore, the kinetic Monte Carlo simulation revealed that the diffusion coefficient estimated by this method tends to be slightly overestimated as the temperature decreases.
Yamamoto, Kazami; Hasegawa, Kazuo; Kinsho, Michikazu; Oguri, Hidetomo; Hayashi, Naoki; Yamazaki, Yoshio; Naito, Fujio*; Yoshii, Masahito*; Toyama, Takeshi*
JPS Conference Proceedings (Internet), 33, p.011016_1 - 011016_7, 2021/03
The Japan Proton Accelerator Research Complex (J-PARC) is a multipurpose facility for scientific experiments. The accelerator complex consists of a 400-MeV Linac, a 3-GeV Rapid-Cycling Synchrotron (RCS) and a 30-GeV Main Ring synchrotron (MR). The RCS delivers a proton beam to the neutron target and MR, and the MR delivers the beams to the neutrino target and the Hadron Experimental Facility. The first operation of the neutron experiments began in December 2008. Following this, the user operation has been continued with some accidental suspensions. These suspensions include the recovery work due to the Great East Japan Earthquake in March 2011 and the radiation leak incident at the Hadron Experimental Facility. In this report, we summarize the major causes of suspension, and the statistics of the reliability of J-PARC accelerator system is analyzed. Owing to our efforts to achieve higher reliability, the Mean Time Between Failure (MTBF) has been improved.
