Faculty Profiles - OHNO, Noriyasu

Localized spiraling plasma ejection contributing the ion-flux broadening in the detached linear plasma Reviewed

Blob- and hole-like structures outstanding during the transition from attached to detached divertor states in GAMMA 10/PDX Reviewed Open Access

Tanaka, H, Sakamoto, M, Ezumi, N, Nojiri, K, Terakado, A, Mikami, T, Kinoshita, Y, Kobayashi, K, Yoshikawa, M, Kohagura, J, Ohno, N

PHYSICS OF PLASMAS Vol. 25 ( 8 ) page： 082505(6 pp) 2018.8

Tanaka, H, Takeyama, K, Yoshikawa, M, Kajita, S, Ohno, N, Hayashi, Y

PLASMA PHYSICS AND CONTROLLED FUSION Vol. 60 ( 7 ) page： 075013 2018.7

Ignition and erosion of materials by arcing in fusion-relevant conditions Reviewed

Hwangbo Dogyun, Kajita Shin, Barengolts Sergey A, Tsventoukh Mikhail M, Kawaguchi Shota, Mesyats Vadim G, Ohno Noriyasu

CONTRIBUTIONS TO PLASMA PHYSICS Vol. 58 ( 6-8 ) page： 608 - 615 2018.7

Helium line emission spectroscopy in recombining detached plasmas Reviewed Open Access

Shin Kajita, Kensuke Suzuki, Hirohiko Tanaka, Noriyasu Ohno

Physics of Plasmas Vol. 25 ( 6 ) page： 063303 2018.6

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：American Institute of Physics Inc.

Line emissions from helium (He) plasmas have been used for measurement of electron density and temperature in various situations. We performed measurements of He line intensities in recombining plasmas in a divertor simulator, followed by discussion of some potential difficulties of using the line intensity ratio (LIR) method in a divertor environment under detached conditions. When using four line emissions (501.6, 667.8, 706.5, and 728.1 nm), the discrepancy of the results compared to results from the laser Thomson scattering (LTS) method increased along with increasing gas pressure. However, the LIR method agreed well with LTS when a recombination sensitive line emission (447.1 nm) was added. The influence of the transport of metastable atoms is also discussed. Additionally, anomalous characteristics of the LIR method were revealed in hydrogen helium mixture plasmas when the temperature was in the range of 1-4 eV. These anomalies were likely attributable to the dissociative recombination of HeH+.

DOI： 10.1063/1.5029414

Nanostructure Growth on Rhodium/Ruthenium by the Exposure to He Plasma Reviewed

Tomohiro NOJIMA, Shin KAJITA, Naoaki YOSHIDA, Shota KAWAGUCHI, Noriyasu OHNO, Hirohiko TANAKA, Masayuki TOKITANI, Daisuke NAGATA, Tsuyoshi AKIYAMA, Takashi YAGI

Plasma and Fusion Research Vol. 13 page： 3406064 2018.6

Mode Structure Analysis of Detached Plasmas with 2D Images Reviewed

Kajita Shin, Tanaka Hirohiko, Ohno Noriyasu, Onda Takuya

PLASMA AND FUSION RESEARCH Vol. 13 page： 1402033(5 pp) 2018.5

Fabrication of photocatalytically active vanadium oxide nanostructures via plasma route Reviewed Open Access

Shin Kajita, Tomoko Yoshida, Noriyasu Ohno, Yusuke Ichino, Naoaki Yoshida

Journal of Physics D: Applied Physics Vol. 51 ( 21 ) page： 215201 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Physics Publishing

Plasma irradiation was used to create nanostructured vanadium oxide with potential commercial and industrial applications. Morphology changes were induced at the nano- and micro-meter scale, accompanied by the growth of helium nanobubbles. Micrometer-sized pillars, cube-shaped nanostructures, and fuzzy fiberform nanostructures were grown on the surface
the necessary conditions in terms of the incident ion energy and the surface temperature for those morphology changes were revealed. Hydrogen production experiments using a photocatalytic reaction with aqueous methanol solution were conducted on the fabricated samples. Enhanced H2 production was confirmed with the plasma irradiated nanostructured sample that had been oxidized in air atmosphere. Photocatalytically inactive vanadium oxide exhibited a high photocatalytic activity after nanostructurization of the surface by helium plasma irradiation.

DOI： 10.1088/1361-6463/aabe44

Fuzzy nanostructure growth on precious metals by He plasma irradiation Reviewed Open Access

Shin Kajita, Tomohiro Nojima, Yudai Tomita, Noriyasu Ohno, Hirohiko Tanaka, Naoaki Yoshida, Miyuki Yajima, Tsuyoshi Akiyama, Masayuki Tokitani, Takashi Yagi

Surface and Coatings Technology Vol. 340 page： 86 - 92 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier B.V.

Growth of helium bubbles near the surface of metals leads to various morphology changes when sufficient helium ions are continuously implanted on the surface. In this study, low energy (&lt
100 eV) helium plasma irradiations to various noble metals were conducted, and consequent surface morphology changes were analyzed. It was found that fiberform nanostructures were formed by the helium plasma irradiation on rhodium and ruthenium thin films, which were deposited by magnetron sputtering, and on platinum and iridium wires. Growth of fiberform structures were not identified on gold, silver, and palladium samples exposed to helium plasmas even though the irradiations were conducted at various surface temperatures, though pinholes were observed on palladium surface. We discussed the relation between the morphology changes and material properties.

DOI： 10.1016/j.surfcoat.2018.02.026

Pulsation Effects of Incident Ion Energy on W Fuzz Growth Reviewed

Kajita Shin, Kawaguchi Shota, Hwangbo Dogyun, Tanaka Hirohiko, Ohno Noriyasu

PLASMA AND FUSION RESEARCH Vol. 13 page： 1205001 2018.1

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

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 Open Access

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

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

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

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

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

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

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 Open Access

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 Open Access

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