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Kim, B. K.*; Tan, L.*; Sakasegawa, Hideo; Parish, C. M.*; Zhong, W.*; Tanigawa, Hiroyasu*; Kato, Yutai*
Journal of Nuclear Materials, 545, p.152634_1 - 152634_12, 2021/03
Times Cited Count：6 Percentile：48.40(Materials Science, Multidisciplinary)Asahi, Yuichi; Fujii, Keisuke*
Purazuma, Kaku Yugo Gakkai-Shi, 97(2), p.86 - 92, 2021/02
The 5D gyrokinetic simulation data has been analyzed with the data-driven analysis methods. By defining an entropy-like quantity with singular values, we have quantitatively evaluated the randomness of the plasma state. We found that the randomness of plasma increases after the avalanche like transport and then gradually decrease. Since the decrease of the randomness is expected to be relevant to the phase space structure formation, we have developed a method to extract the phase space structures from the time series of 5D data. The relationship between the avalanche-like transport and phase space structures is discussed based on the contribution of each principal component to the energy transport.
Asahi, Yuichi; Fujii, Keisuke*; Heim, D. M.*; Maeyama, Shinya*; Garbet, X.*; Grandgirard, V.*; Sarazin, Y.*; Dif-Pradalier, G.*; Idomura, Yasuhiro; Yagi, Masatoshi*
Physics of Plasmas, 28(1), p.012304_1 - 012304_21, 2021/01
Times Cited Count：7 Percentile：35.87(Physics, Fluids & Plasmas)This article demonstrates a data compression technique for the time series of five dimensional distribution function data based on Principal Component Analysis (PCA). Phase space bases and corresponding coefficients are constructed by PCA in order to reduce the data size and the dimensionality. It is shown that about 83% of the variance of the original five dimensional distribution can be expressed with 64 components. This leads to the compression of the degrees of freedom from 
to 
. One of the important findings - resulting from the detailed analysis of the contribution of each principal component to the energy flux - deals with avalanche events, which are found to be mostly driven by coherent structures in the phase space, indicating the key role of resonant particles.
Uenaga, Issei; Furukawa, Masaru*
Physics of Plasmas, 27(9), p.092501_1 - 092501_11, 2020/09
Times Cited Count：1 Percentile：3.58(Physics, Fluids & Plasmas)This work uses the Rutherford model for a cylindrical plasma to study the dynamics of magnetic islands under external magnetic perturbations, including both applied rotational magnetic fields and static error magnetic fields. The results show that, in an unstable tearing situation, magnetic islands are completely suppressed by modulating the frequency of the externally applied rotational magnetic field to maintain the phase of the combined external magnetic field to be opposite (or nearly opposite) that of the magnetic islands. The frequency is modulated by using a proportional controller in the simulation, where the frequency of the rotational field is determined by using the island rotation frequency "measured" in the simulation.
Kondo, Hiroo*; Kanemura, Takuji*; Park, C. H.*; Oyaizu, Makoto*; Hirakawa, Yasushi; Furukawa, Tomohiro
Fusion Engineering and Design, 146(Part A), p.285 - 288, 2019/09
Times Cited Count：1 Percentile：7.90(Nuclear Science & Technology)Herein, the wall shear stress in a double contraction nozzle has been evaluated experimentally to produce a liquid lithium (Li) target as a beam target for intense fusion neutron sources such as the International Fusion Materials Irradiation Facility (IFMIF), the Advanced Fusion Neutron Source (A-FNS), and the DEMO Oriented Neutron Source (DONES). The boundary layer thickness and wall shear stress are essential physical parameters to understand erosion-corrosion by the high-speed liquid Li flow in the nozzle, which is the key component in producing a stable Li target. Therefore, these parameters were experimentally evaluated using an acrylic mock-up of the target assembly. The velocity distribution in the nozzle was measured by a laser-doppler velocimeter and the momentum thickness along the nozzle wall was calculated using an empirical prediction method. The resulting momentum thickness was used to estimate the variation of the wall shear stress along the nozzle wall. Consequently, the wall shear stress was at the maximum in the second convergent section in front of the nozzle exit.
Donnel, P.*; Garbet, X.*; Sarazin, Y.*; Asahi, Yuichi; Wilczynski, F.*; Caschera, E.*; Dif-Pradalier, G.*; Ghendrih, P.*; Gillot, C.*
Plasma Physics and Controlled Fusion, 61(1), p.014003_1 - 014003_11, 2019/01
Times Cited Count：14 Percentile：56.84(Physics, Fluids & Plasmas)Poloidal asymmetries of the 
plasma flow are known to play a role in neoclassical transport. According to conventional neoclassical theory, the level of poloidal asymmetry of the electric potential is expected to be very small. In the present work, a general framework for the generation of axisymmetric structures of potential by turbulence is presented. Zonal flows, geodesic acoustic modes and convective cells are described by a single model. This is done by solving the gyrokinetic equation coupled to the quasi-neutrality equation. This calculation provides a predictive calculation of the frequency spectrum of flows given a specified forcing due to turbulence. It also shows that the dominant mechanism comes from zonal flow compression at intermediate frequencies, while ballooning of the turbulence Reynolds stress appears to be the main drive at low frequency.
Kondo, Hiroo*; Kanemura, Takuji*; Hirakawa, Yasushi; Furukawa, Tomohiro
Fusion Engineering and Design, 136(Part A), p.24 - 28, 2018/11
Times Cited Count：3 Percentile：23.73(Nuclear Science & Technology)In the IFMIF-EVEDA project, we designed and constructed the IFMIF-EVEDA Li Test Loop (ELTL), and we performed experiments to validate the stability of the Li target. This project required a diagnostic tool to be developed in order to examine the Li target; as such, we developed a unique laser-based method that we call the laser-probe method; this method combines a high-precision laser distance meter with a statistical data analysis method. Following the successful development of the laser-probe method, we proposes a long-distance-measurement of the laser probe method (long-distance LP method) as a diagnostics tool in off-beam conditions for IFMIF or the relevant neutron sources. In this study, the measurement uncertainty resulting from coherency of the laser in a long-distance-measurement has been verified by using stationary objects and a water jet simulating the liquid Li target.
Saito, Makiko; Kozaka, Hiroshi; Maruyama, Takahito; Noguchi, Yuto; Takeda, Nobukazu; Kakudate, Satoshi; 1 of others*
Fusion Engineering and Design, 124, p.542 - 547, 2017/11
Times Cited Count：6 Percentile：43.28(Nuclear Science & Technology)Tojo, Hiroshi; Hatae, Takaki; Hamano, Takashi; Itami, Kiyoshi
Fusion Engineering and Design, 123, p.678 - 681, 2017/11
Times Cited Count：5 Percentile：37.05(Nuclear Science & Technology)Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku*; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*
Scientific Reports (Internet), 7(1), p.14971_1 - 14971_8, 2017/11
Times Cited Count：30 Percentile：79.92(Multidisciplinary Sciences)Tanigawa, Hiroyasu; Gaganidze, E.*; Hirose, Takanori; Ando, Masami; Zinkle, S. J.*; Lindau, R.*; Diegele, E.*
Nuclear Fusion, 57(9), p.092004_1 - 092004_13, 2017/06
Times Cited Count：145 Percentile：99.21(Physics, Fluids & Plasmas)The current status of RAFM developments and evaluations, including the applicability of joining technologies, is reviewed. The technical challenges and potential risks of utilizing RAFM steels as the structural material of in-vessel components are discussed, and possible mitigation methodology is introduced. The discussion suggests that deuterium-tritium fusion neutron irradiation effects currently need to be treated as an ambiguity factor which could be incorporated within the safety factor. The safety factor will be defined by the engineering design criteria which are not yet developed with regard to irradiation effects and some high temperature process, and the operating time condition of the in-vessel component will be defined by the condition at which those ambiguities due to neutron irradiation become too large to be acceptable, or by the critical condition at which 14 MeV fusion neutron irradiation effects is expected to become different from fission neutron irradiation effects.
Bhattacharya, R.*; Vaghela, H.*; Sarkar, B.*; Patel, P.*; Das, J.*; Srinivasa, M.*; Isono, Takaaki; Kawano, Katsumi
IOP Conference Series; Materials Science and Engineering, 171, p.012058_1 - 012058_8, 2017/03
Furukawa, Tomohiro; Hirakawa, Yasushi; Kondo, Hiroo; Kanemura, Takuji
Nuclear Materials and Energy (Internet), 9, p.286 - 291, 2016/12
Times Cited Count：12 Percentile：68.05(Nuclear Science & Technology)In order to exchange the components which received irradiation damage during the operation at the International Fusion Materials Irradiation Facility, the adhered lithium, which is partially converted to lithium compounds such as lithium oxide and lithium hydroxide, should be removed from the components. In this study, the dissolution experiments of lithium compounds (lithium nitride, lithium hydroxide, and lithium oxide) were performed in a candidate solvent, allowing the clarification of time and temperature dependence. Based on the results, a cleaning procedure for adhered lithium on the inner surface of the components was proposed.
Iwai, Yasunori; Edao, Yuki; Asahara, Hiroo*; Hayashi, Takumi
Nuclear Materials and Energy (Internet), 9, p.267 - 272, 2016/12
Times Cited Count：6 Percentile：43.06(Nuclear Science & Technology)Tritium oxidation over noble catalyst is a fundamental reaction in the fusion fields since the system of catalytic reactor for the oxidation of tritium in combination with following tritiated vapor absorber has been applied in tritium handling facilities to control the tritium release into the environment as low as achievable. To enhance tritium safety as much as possible with taking severe accidents such as complete loss of power supply into account, technology of hydrophobic catalyst has been drawing intense interest recently because of its potential application in passive recombiner for tritium oxidation at room temperature. To design a passive recombiner packed with hydrophobic catalyst for tritium oxidation, the development of manufacturing technology for hydrophobic platinum catalyst and the following data on reaction rate are essential. This presentation deals with the reaction rate for tritium oxidation over hydrophobic platinum catalyst at temperatures from room temperature to 343 K. Two kinds of hydrophobic platinum catalysts; supported with styrene-divinylbenzene and with silica were used for this test. The results indicate that (1) the reaction rate is effected by the particle size of platinum, (2) the order of reaction is 0.5 of hydrogen concentration at room temperature. The rate-determining step approximation method is applied for the discussion on the reaction mechanism of tritium oxidation over platinum catalyst.
TiO
with Li
ZrO
Hoshino, Tsuyoshi
Nuclear Materials and Energy (Internet), 9, p.221 - 226, 2016/12
Times Cited Count：50 Percentile：96.87(Nuclear Science & Technology)Demonstration power plant (DEMO) reactors require advanced tritium breeders with high tritium breeding ratios (TBRs) and increased stability at high temperatures. LiTiO with excess Li (LiTiO) is one of the candidate materials for advanced tritium breeders. While LiTiO pebbles have some good properties, the TBR in LiTiO is smaller than that in LiO because of its low Li density. Therefore, new Li-contained ceramic composites with not only high stability but also high Li density have been developed in JAEA. I focused on a solid solution with a new characteristic. Since the atomic radius of Li and Zr is similar, I surveyed the possibility of solid solution for a LiO-TiO-ZrO (LTZO) system. The solid solution pebbles of LTZO are fabricated by an emulsion method are designated as LTZO20 (LiTiO with added 20 wt% LiZrO). The X-ray diffraction patterns of the sintered LTZO20 pebbles are approximately the same as those of LiTiO pebbles, and then LiZrO disappeared. The results show that LTZO pebbles are not a two-phase material but a solid solution.
Nakamichi, Masaru; Kim, Jae-Hwan; Miyamoto, Mitsutaka*
Nuclear Materials and Energy (Internet), 9, p.55 - 58, 2016/12
Times Cited Count：23 Percentile：86.30(Nuclear Science & Technology)Edao, Yuki; Iwai, Yasunori; Hayashi, Takumi
Nuclear Materials and Energy (Internet), 9, p.273 - 277, 2016/12
Times Cited Count：5 Percentile：37.50(Nuclear Science & Technology)Wakai, Eiichi; Kanemura, Takuji; Kondo, Hiroo; Hirakawa, Yasushi; Ito, Yuzuru*; Higashi, Takuma*; Suzuki, Akihiro*; Fukada, Satoshi*; Yagi, Juro*; Tsuji, Yoshiyuki*; et al.
Nuclear Materials and Energy (Internet), 9, p.278 - 285, 2016/12
Times Cited Count：11 Percentile：64.76(Nuclear Science & Technology)The EVEDA (Engineering Validation and Engineering Design Activity) lithium test loop with the world's highest flow rate was constructed and has been operated mainly at 250
C. It succeeded in generating a 100 mm wide and 25 mm thick free-surface lithium flow along a concave back plate steadily at a high-speed of 15 m/s at 250C for 1,300 h under the Broader Approach Activities. A new wave height measuring method (laser-probe method) was developed for measurements of the 3D geometry of the liquid Li target surface. Using the device, the stability of the Li flow (the thickness variation of 
1 mm or less) required for the actual liquid Li target of the IFMIF was satisfied and the feasibility of the long-term stable liquid Li flow was verified. The results of the other engineering validation tests such as lithium purification tests and the engineering design of lithium facility have also been evaluated and summarized.
Oyaizu, Makoto; Isobe, Kanetsugu; Hayashi, Takumi
Nuclear Materials and Energy (Internet), 9, p.508 - 511, 2016/12
Times Cited Count：2 Percentile：16.63(Nuclear Science & Technology)Stainless steels of SS304, SS316L and such will be widely used in fusion reactor. Corrosion of such metals is an important issue for the establishment of safety and soundness of fusion reactors. It has recently been reported that the passivation of SS304 stainless steel was inhibited in tritiated solution, resulting in significant corrosion enhancement. Therefore in the present study, the effects of tritium on the passivation behavior of SS316L stainless steel in tritiated water circumstance is electrochemically studied by comparing to those of SS304 stainless steel previously studied. As the results, it was found that no significant effects of tritium on the passivation behavior of SS316L stainless steel could be observed, which is contrary to that of SS304 stainless steel.
Ioki, Kimihiro*; Hiranai, Shinichi; Moriyama, Shinichi; Tanaka, Suguru*
Fusion Engineering and Design, 109-111(Part A), p.951 - 955, 2016/11
Times Cited Count：5 Percentile：37.50(Nuclear Science & Technology)A dummy load dissipates the RF power and is required to test and adjust a gyrotron or a transmission line. The most critical issue is long-term reliability in the vacuum and coolant boundary of the rotation mechanism for current large-scale dummy loads. A new design has been developed to use linear movement for the reflector assembly to mitigate the heat deposition concentration. The thickness distribution of the ceramic layer is carefully analyzed and optimized. A prototypical dummy load will be manufactured as the next step.
