Faculty Profiles - OHNO, Noriyasu

Papers - OHNO, Noriyasu

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Measurement of He neutral temperature in detached plasmas using laser absorption spectroscopy Reviewed

Aramaki M., Tsujihara T., Kajit S., Tanaka H., Ohno N.

AIP ADVANCES Vol. 8 ( 1 ) page： 015308 2018.1

Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas Reviewed

Aiba N., Pamela S., Honda M., Urano H., Giroud C., Delabie E., Frassinetti L., Lupelli I., Hayashi N., Huijsmans G.T.A., Litaudon X., Abduallev S., Abhangi M., Abreu P., Afzal M., Aggarwal K.M., Ahlgren T., Ahn J.H., Aho-Mantila L., Airila M., Albanese R., Aldred V., Alegre D., Alessi E., Aleynikov P., Alfier A., Alkseev A., Allinson M., Alper B., Alves E., Ambrosino G., Ambrosino R., Amicucci L., Amosov V., Sundén E.A., Angelone M., Anghel M., Angioni C., Appel L., Appelbee C., Arena P., Ariola M., Arnichand H., Arshad S., Ash A., Ashikawa N., Aslanyan V., Asunta O., Auriemma F., Austin Y., Avotina L., Axton M.D., Ayres C., Bacharis M., Baciero A., Baião D., Bailey S., Baker A., Balboa I., Balden M., Balshaw N., Bament R., Banks J.W., Baranov Y.F., Barnard M.A., Barnes D., Barnes M., Barnsley R., Wiechec A.B., Orte L.B., Baruzzo M., Basiuk V., Bassan M., Bastow R., Batista A., Batistoni P., Baughan R., Bauvir B., Baylor L., Bazylev B., Beal J., Beaumont P.S., Beckers M., Beckett B., Becoulet A., Bekris N., Beldishevski M., Bell K., Belli F., Bellinger M., Belonohy , Ayed N.B., Benterman N.A., Bergsåker H., Bernardo J., Bernert M., Berry M., Bertalot L., Besliu C., Beurskens M.

Plasma Physics and Controlled Fusion Vol. 60 ( 1 ) 2018.1

Language：Japanese Publisher：Plasma Physics and Controlled Fusion

The stability with respect to a peelingballooning mode (PBM) was investigated numerically with extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift (w∗i), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into account both the rotation and w∗i effects in the numerical analysis. When deuterium poloidal rotation is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes the PBM because of an acceleration of rotation and a decrease in w∗i. The difference in the amount of ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the difference in the linear stability property, due not to the rotation direction but to the plasma density profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and w∗i effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.

DOI： 10.1088/1361-6587/aa8bec

Scopus

Enhanced growth of large-scale nanostructures with metallic ion precipitation in helium plasmas Reviewed

Shin Kajita, Shota Kawaguchi, Noriyasu Ohno, Naoaki Yoshida

Scientific Reports Vol. 8 page： 56 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Nature Publishing Group

Helium plasma irradiation on metal surfaces leads to the formation of metallic fuzzy nanostructures accompanied by the growth of helium bubbles in metals. The mechanism of the growth process, its impact for fusion devices, and potential application have been explored. Here we show enhanced growth of large-scale fuzz by precipitating additional metallic particles during helium plasma irradiation. The growth rate of the fuzzy structures became orders of magnitude greater than conventional fuzz growth
in an hour of irradiation, 1 mm-thick visible tungsten and molybdenum fuzzy fur structures covered a tungsten metal substrate. Additional precipitation of metallic ions breaks the bottleneck diffusion process
moreover, further acceleration in the growth rate could have occurred if the electric sheath shape was influenced by the grown structure and the electric field that formed around the structure started collecting ions.

DOI： 10.1038/s41598-017-18476-7

Web of Science

Scopus

Morphology Changes of Platinum and Tungsten Carbide by He Plasma Irradiation Reviewed

Tomita Yudai, Kajita Shin, Ohno Noriyasu, Tanaka Hirohiko, Ichino Yusuke

PLASMA AND FUSION RESEARCH Vol. 13 page： 3406074 2018

Recent progress of divertor simulation research using the GAMMA 10/PDX tandem mirror Reviewed

Nakashima Y, Ichimura K, Islam M. S, Sakamoto M, Ezumi N, Hirata M, Ichimura M, Ikezoe R, Imai T, Kariya T, Katanuma I, Kohagura J, Minami R, Numakura T, Yoshikawa M, Iijima T, Islam M. M, Nojiri K, Shimizu K, Terakado A, Togo S, Asakura N, Fukumoto M, Hatayama A, Hirooka Y, Kado S, Kubo H, Masuzaki S, Matsuura H, Nakano T, Nagata S, Nishino N, Ohno N, Sagara A, Sawada K, Shoji M, Tonegawa A, Ueda Y

NUCLEAR FUSION Vol. 57 ( 11 ) 2017.11

Language：English Publishing type：Research paper (scientific journal)

© 2017 IAEA, Vienna. This paper describes the recent progress in divertor simulation research using the GAMMA 10/PDX tandem mirror towards the development of divertors in fusion reactors. During a plasma flow generation experiment in the end cell of the GAMMA 10/PDX, ICRF heating in the anchor cell successfully extended the particle flux up to 3.3 1023 m2 s-1. Superimposing the short pulse of the ECH also attained a maximum heat flux of ∼30 MW m-2. We have succeeded in achieving and characterizing the detachment of the high-temperature plasma, which is equivalent to the SOL plasma of tokamaks, by using the divertor simulation experimental module (D-module) in the GAMMA 10/PDX end cell, in spite of using a linear device with a short magnetic field line connection length. Various gases (Ar, Xe, Ne and N2) are examined to evaluate the effect of radiation cooling against the plasma flow at the MW m-2 level in the divertor simulation region and the following results are obtained: (i) Xe gas was most effective in the reduction of heat and particle fluxes (1%, 3%, respectively) and has a stronger effect on electron cooling (down to ∼1.6 eV) in the used gas species. (ii) Ne gas was less effective. On the other hand, (iii) N2 gas showed more favorable effects than Ar in the lower pressure range. These results will contribute to the progress in detached plasma operation and in clarifying the radiation cooling mechanism towards the development of future divertors.

DOI： 10.1088/1741-4326/aa7cb4

Web of Science

Scopus

Development of a Compact Divertor Plasma Simulator for Plasma-Wall Interaction Studies on Neutron-Irradiated Materials Reviewed

N.Ohno, T.Kuwabara, M.Takagi, R.Nishimura, M.Yajima, A.Sagara, T.Toyama, K.Suzuki, H.Kurishita, T.Shikama, Y.Hatano, N.Yoshida

Plasma and Fusion Research Vol. 12 ( 0 ) page： 1405040 - 1405040 2017.10

Studies of power exhaust and divertor design for a 1.5 GW-level fusion power DEMO Reviewed

N.Asakura, K.Hoshino, S.Suzuki, S.Tokunaga, Y.Someya, H.Utoh, H.Kudo, Y.Sakamoto, R.Hiwatari, K.Tobita, K.Shimizu, K.Ezato, Y.Seki, N.Ohno, Y.Ueda, Joint Special Team for DEMO Design

Nuclear Fusion Vol. 57 page： 126050(12 pp) 2017.10

Plasma Exhaust and Divertor Studies in JA and EU Broader Tokamak Fusion Reactor Approach, DEMO Design Activity Reviewed

Nobuyuki Asakura, Kazuo Hoshino, Hiroyasu Utoh, Yoji Someya, Satoshi Suzuki, Christian Bachmann, Holger Reimerdes, Hironobu Kudo, Shinsuke Tokunaga, Yuki Homma, Yoshiteru Sakamoto, Ryoji Hiwatari, Ronald Wenninger, Kenji Tobita, Noriyasu Ohno,Gianfranco Federici, Koichiro Ezato, Yohji Seki, Noriyasu Ohno, Yoshio Ueda

2017.9

Extension of the operational regime of the LHD towards a deuterium experiment Reviewed

Takeiri Y., Morisaki T., Osakabe M., Yokoyama M., Sakakibara S., Takahashi H., Nakamura Y., Oishi T., Motojima G., Murakami S., Ito K., Ejiri A., Imagawa S., Inagaki S., Isobe M., Kubo S., Masamune S., Mito T., Murakami I., Nagaoka K., Nagasaki K., Nishimura K., Sakamoto M., Sakamoto R., Shimozuma T., Shinohara K., Sugama H., Watanabe K. Y., Ahn J. W., Akata N., Akiyama T., Ashikawa N., Baldzuhn J., Bando T., Bernard E., Castejon F., Chikaraishi H., Emoto M., Evans T., Ezumi N., Fujii K., Funaba H., Goto M., Goto T., Gradic D., Gunsu Y., Hamaguchi S., Hasegawa H., Hayashi Y., Hidalgo C., Higashiguchi T., Hirooka Y., Hishinuma Y., Horiuchi R., Ichiguchi K., Ida K., Ido T., Igami H., Ikeda K., Ishiguro S., Ishizaki R., Ishizawa A., Ito A., Ito Y., Iwamoto A., Kamio S., Kamiya K., Kaneko O., Kanno R., Kasahara H., Kato D., Kato T., Kawahata K., Kawamura G., Kisaki M., Kitajima S., Ko W. H., Kobayashi M., Kobayashi S., Kobayashi T., Koga K., Kohyama A., Kumazawa R., Lee J. H., Lopez-Bruna D., Makino R., Masuzaki S., Matsumoto Y., Matsuura H., Mitarai O., Miura H., Miyazawa J., Mizuguchi N., Moon C., Morita S., Moritaka T., Mukai K., Muroga T., Muto S., Mutoh T., Nagasaka T., Nagayama Y., Nakajima N., Nakamura Y., Nakanishi H., Nakano H., Nakata M., Narushima Y., Nishijima D., Nishimura A., Nishimura S., Nishitani T., Nishiura M., Nobuta Y., Noto H., Nunami M., Obana T., Ogawa K., Ohdachi S., Ohno M., Ohno N., Ohtani H., Okamoto M., Oya Y., Ozaki T., Peterson B. J., Preynas M., Sagara S., Saito K., Sakaue H., Sanpei A., Satake S., Sato M., Saze T., Schmitz O., Seki R., Seki T., Sharov I., Shimizu A., Shiratani M., Shoji M., Skinner C., Soga R., Stange T., Suzuki C., Suzuki Y., Takada S., Takahata K., Takayama A., Takayama S., Takemura Y., Takeuchi Y., Tamura H., Tamura N., Tanaka H., Tanaka K., Tanaka M., Tanaka T., Tanaka Y., Toda S., Todo Y., Toi K., Toida M., Tokitani M., Tokuzawa T., Tsuchiya H., Tsujimura T., Tsumori K., Usami S., Velasco J. L., Wang H., Watanabe T. -H., Watanabe T., Yagi J., Yajima M., Yamada H., Yamada I., Yamagishi O., Yamaguchi N., Yamamoto Y., Yanagi N., Yasuhara R., Yatsuka E., Yoshida N., Yoshinuma M., Yoshimura S., Yoshimura Y.

NUCLEAR FUSION Vol. 57 ( 10 ) 2017.8

Erosion of nanostructured tungsten by laser ablation, sputtering and arcing Reviewed

Dogyun Hwangbo, Shota Kawaguchi, Shin Kajita, Noriyasu Ohno

Nuclear Materials and Energy Vol. 12 page： 386 - 391 2017.8

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

Mass loss of nanostructured tungsten, which was formed by helium plasma irradiation, due to laser ablation, sputtering, and arcing was investigated. Below the helium sputtering energy threshold (&lt
117 eV), sputtering by impurity gases such as nitrogen and oxygen was dominant. Sputtering yield became closer to theoretical value with increasing the incident ion energy, and sputtering by helium ions became the major contribution when the energy was &gt
200 eV. Reduction in sputtering on nanostructured surface was observed. Arcing was initiated using laser pulses, and the erosion rate by arcing was measured. The erosion rate increased with arc current, while the erosion per Coulomb was not affected by arc current.

DOI： 10.1016/j.nme.2017.03.004

Web of Science

Scopus

Measuring temperature effects on nano-bubble growth in tungsten with grazing incidence small angle X-ray scattering Reviewed

Matt Thompson, Russ Doerner, Noriyasu Ohno, Nigel Kirby, Patrick Kluth, Daniel Riley, Cormac Corr

Nuclear Materials and Energy Vol. 12 page： 1294 - 1297 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

W samples were exposed to He plasma in the MAGPIE, NAGDIS-II and PISCES-A across a range of sample temperatures between 473–1123 K. GISAXS was used to quantify the effect of plasma fluence and W surface temperature on He nano-bubble size distributions. In NAGDIS-II at 873 K nano-bubbles are exponentially distributed with mean diameters μ=0.64±0.01nm, similar to the value of μ=0.62±0.01nmfound for the MAGPIE plasma device at the much lower temperature of 473 K. Above ∼900 K nano-bubbles followed an approximately exponential distribution with μ &gt
0.72 nm demonstrating a significant increase in nano-bubble sizes at higher temperatures.

DOI： 10.1016/j.nme.2016.11.025

Web of Science

Scopus

A Particle-In-Cell approach to particle flux shaping with a surface mask Reviewed

Kawamura G, Ohno N, Takamura S, Tomita Y

NUCLEAR MATERIALS AND ENERGY Vol. 12 page： 297 - 301 2017.8

Toroidally symmetric/asymmetric effect on the divertor flux due to neon/nitrogen seeding in LHD Reviewed

H. Tanaka, G. Kawamura, S. Masuzaki, M. Kobayashi, T. Akiyama, B.J. Peterson, K. Mukai, R. Sano, S.Y. Dai, R. Sakamoto, T. Morisaki, N. Ohno, LHD Experiment Group

Nucl. Mater. Energy Vol. 12 page： 241 - 246 2017.8

Molecular activated recombination in divertor simulation plasma on GAMMA 10/PDX Reviewed

Sakamoto M, Terakado A, Nojiri K, Ezumi N, Nakashima Y, Sawada K, Ichimura K, Fukumoto M, Oki K, Shimizu K, Ohno N, Masuzaki S, Togo S, Kohagura J, Yoshikawa M

NUCLEAR MATERIALS AND ENERGY Vol. 12 page： 1004 - 1009 2017.8

Fractality and growth of He bubbles in metals Reviewed

Shin Kajita, Atsushi M. Ito, Noriyasu Ohno

PHYSICS LETTERS A Vol. 381 ( 29 ) page： 2355 - 2362 2017.8

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Pinholes are formed on surfaces of metals by the exposure to helium plasmas, and they are regarded as the initial process of the growth of fuzzy nanostructures. In this study, number density of the pinholes is investigated in detail from the scanning electron microscope (SEM) micrographs of tungsten and tantalum exposed to the helium plasmas. A power law relation was identified between the number density and the size of pinholes. From the slope and the region where the power law was satisfied, the fractal dimension D and s(min), which characterize the SEM images, are deduced. Parametric dependences and material dependence of D and s(min) are revealed. To explain the fractality, simple Monte-Carlo simulations including random walks of He atoms and absorption on bubble was introduced. It is shown that the initial position of the random walk is one of the key factors to deduce the fractality. The results indicated that new nucleations of bubbles are necessary to reproduce the number-density distribution of bubbles. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physleta.2017.05.028

Web of Science

Scopus

Field Emission From Metal Surfaces Irradiated With Helium Plasmas Reviewed International coauthorship

Dogyun Hwangbo, Shin Kajita, Noriyasu Ohno, Dmitry Sinelnikov

IEEE TRANSACTIONS ON PLASMA SCIENCE Vol. 45 ( 8 ) page： 2080 - 2086 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Field electron emission from metal (tungsten, molybdenum, and tantalum) surfaces with different surface morphology was measured. Fuzz and loop samples had small increment in the emission current, whereas bubble samples marked huge increment in the current, accompanied by breakdown. The emission current became greater on the fuzzy samples than the loop samples probably because of more elongated morphology of fuzzy fiber. Among the materials, molybdenum had the lowest current. From Fowler-Nordheim plot analysis, it was revealed that fuzz samples had higher field enhancement factor than loop samples. Bubble samples marked the highest value in the field enhancement factor among the three types of morphology, likely due to the continuous emission from the craters formed after the breakdown. Molybdenum showed favorable properties in terms of suppressing the field emission and preventing the breakdown and the arcing in fusion reactor. From the scanning electron microscope observation, the size of the crater increases with the emission current on the bubble samples. Fuzzy structure was observed at the crater on the tantalum bubble surface after breakdown even without stationary plasma irradiation or stationary incidence of ion flux.

DOI： 10.1109/TPS.2017.2679211

Web of Science

Scopus

Effects of modified surfaces produced at plasma-facing surface on hydrogen release behavior in the LHD Reviewed

Nobuta Y, Masuzaki S, Tokitani M, Ashikawa N, Nagata D, Yoshida N, Oya Y, Yajima M, Motojima G, Kasahara H, Miyamoto M, Ohno N, Yamauchi Y

NUCLEAR MATERIALS AND ENERGY Vol. 12 page： 483 - 487 2017.8

Behavior of 23S metastable state He atoms in low-temperature recombining plasmas Reviewed

S.Kajita, T.Tsujihara, M.Aramaki, H.van der Meiden, H.Oshima, N.Ohno, H.Tanaka, R.Yasuhara, T.Akiyama, K.Fujii, T.Shikama

Physics of Plasmas Vol. 24 page： 073301(8 pp) 2017.6

Influence of expanding and contracting magnetic field configurations on detached plasma formation in a linear plasma device Reviewed

Y.Hayashi, N.Ohno, S.Kajita, H.Tanaka

Physics of Plasmas Vol. 24 page： 062509(8 pp) 2017.6

Recent progress of the JT-60SA project Reviewed International coauthorship International journal

Shirai H., Barabaschi P., Kamada Y., Maksoud W.A., Aiba N., Akiyama T., Alonso J., Angioni C., Arai T., Arakawa H., Ardellier F., Artaud J.F., Asakura N., Ashikawa N., Barbato E., Barrera G., Baruzzo M., Baulaigue O., Beaufils S., Bécoulet M., Benkadda S., Benoit F., Bettini P., Beurskens M., Bierwage A., Boboc A., Boccaccini L., Bolzonella T., Bonne F., Borba D., Botija J., Bourdelle C., Brolatti G., Bruschi A., Bucalossi J., Cabrera-Pérez S., Canton A., Cardella A., Carvalho I., Challis C., Chapman I., Chiba S., Ciazynski D., Cismondi F., Clement-Lorenzo S., Coccoluto G., Cocilovo V., Coda S., Coelho R., Coletti A., Collin B., Conway G., Corato V., Costa P., Crisanti F., Cristofani C., Cruz N., Cucchiaro A., Dairaku M., Davis S., Day C., de Baar M., de la Luna E., De Tommasi G., De Vellis A., De Vries P., Decker J., Decool P., Delrez C., Di Pace L., Di Pietro E., Disset G., Donati A., Douai D., Dougnac H., Duchateau J.L., Duglue D., Dumas N., Dunai D., Ejiri A., Endo Y., Enoeda M., Falchetto G., Farina D., Farthing J., Fejoz P., Fernandez P., Ferro A., Fiamozzi-Zignani C., Fietz W., Figini L., Frello G., Frosi P., Fujita T., Fukuda T., Fukumoto M., Fukuyama A., Furukawa M., Furukawa M.

Nuclear Fusion Vol. 57 ( 10 ) 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Nuclear Fusion

The JT-60SA project has been implemented for the purpose of an early realization of fusion energy. With a powerful and versatile NBI and ECRF system, a flexible plasma-shaping capability, and various kinds of in-vessel coils to suppress MHD instabilities, JT-60SA plays an essential role in addressing the key physics and engineering issues of ITER and DEMO. It aims to achieve the long sustainment of high integrated performance plasmas under the high β N condition required in DEMO. The fabrication and installation of components and systems of JT-60SA procured by the EU and Japan are steadily progressing. The installation of toroidal field (TF) coils around the vacuum vessel started in December 2016. The commissioning of the cryogenic system and power supply system has been implemented in the Naka site, and JT-60SA will start operation in 2019. The JT-60SA research plan covers a wide area of issues in ITER and DEMO relevant operation regimes, and has been regularly updated on the basis of intensive discussion among European and Japanese researchers.

DOI： 10.1088/1741-4326/aa5d01

Scopus

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Papers - OHNO, Noriyasu