Faculty Profiles - OHNO, Noriyasu

Papers - OHNO, Noriyasu

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Influence of heavier impurity deposition on surface morphology development and sputtering behavior explored in multiple linear plasma devices Reviewed International coauthorship

D.Nishijima, A.Kreter, M.Baldwin, D.Borodin, A.Eksaeva, D.Hwangbo, S.Kajita, M.Miyamoto, N.Ohno, M.Patino, A.Psopieszczyk, M.Rasinski, T.Schlummer, A.Terra, R.P.Doerner

NUCLEAR MATERIALS AND ENERGY Vol. 18 page： 67 - 71 2019.1

Spatiotemporal Structure of H alpha Emission from the Detached Plasma in GAMMA 10/PDX Reviewed

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

PLASMA AND FUSION RESEARCH Vol. 14 ( Specialissue1 ) page： 2402036(5 pp) 2019.1

Effect of Damage Introduction and He Existence on D Retention in Tungsten by High Flux D Plasma Exposure Reviewed

Yasuhisa Oya, Keisuke Azuma, Akihiro Togari, Moeko Nakata, Qilai Zhou, Mingzhong Zhao, Tatsuya Kuwabara, Noriyasu Ohno, Miyuki Yajima, Yuji Hatano, Takeshi Toyama

Lecture Notes in Networks and Systems Vol. 53 ( 8 ) page： 89 - 96 2019

Proton scattering from tungsten fuzz

D. Bulgadaryan, D. Sinelnikov, V. Kurnaev, S. Kajita, D. Hwangbo, N. Ohno

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms Vol. 434 page： 9 - 12 2018.11

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

© 2018 Elsevier B.V. Tungsten fuzz is a nanostructure formed on tungsten surface under helium plasma impact. In this work, we investigate this structure using the scattering of keV-energy protons. Energy spectra of scattered protons have double-peak shape that corresponds to the scattering from fuzz and underlying pure tungsten. The energy losses of protons in fuzz are estimated as the difference between primary beam energy and the energy corresponding to the local minimum between two peaks. Computer simulations with SRIM code also demonstrate double-peak shape of energy spectra of protons scattered from fuzzy target. Fuzz and pure tungsten stopping powers for protons are compared and fuzz density relative to pure tungsten is estimated and discussed. Evolution of H+energy spectra during fuzz irradiation by Ar+beam is measured and discussed.

DOI： 10.1016/j.nimb.2018.07.038

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Scopus

Plasma exhaust and divertor studies in Japan and Europe broader approach, DEMO design activity Reviewed International coauthorship

N.Asakura, K.Hoshino , H.Utoh, Y.Someya, S.Suzuki, C.Bachmann, H.Reimerdes, R.Wenninger, H.Kudo, S.Tokunaga, Y.Hommai, Y.Sakamoto, R.Hiwatari, K.Tobita, Jeong-Ha You, G.Federici, K.Ezato, Y.Seki, ...N.Ohno

FUSION ENGINEERING AND DESIGN Vol. 136 page： 1214 - 1220 2018.11

Characterized divertor footprint profile modification with the edge pressure gradient in the Large Helical Device Reviewed

Tanaka H., Masuzaki S., Kawamura G., Kobayashi M., Suzuki Y., Motojima G., Murase T., Morisaki T., Ohno N.

PLASMA PHYSICS AND CONTROLLED FUSION Vol. 60 ( 12 ) page： 125001 2018.10

Morphologies of co-depositing W layer formed during He plasma irradiation Reviewed

Kajita Shin, Kawaguchi Shota, Yoshida Naoaki, Ohno Noriyasu, Tanaka Hirohiko

NUCLEAR FUSION Vol. 58 ( 10 ) page： 106002 2018.10

One-Step Plasma Synthesis of Nb<inf>2</inf>O<inf>5</inf> Nanofibers and their Enhanced Photocatalytic activity Reviewed

S.Kajita, F.Mimuro, T.Yoshida, N.Ohno, N.Yoshida

ChemPhysChem Vol. 19 ( 23 ) page： 3237 - 3246 2018.9

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

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Fiberform nanostructured niobium (Nb) was fabricated by one step helium (He) plasma irradiation. He ion implantation formed He nano-bubbles on a Nb plate and led to formation of protrusions while migrating in Nb matrix; fiberform nanostructures (FN) were grown when the fluence became high (>1026 m−2). The necessary conditions for the formation of Nb FN were revealed to be the surface temperature range of 900–1100 K and the incident ion energy higher than 70 eV. The sample was oxidized at 573–773 K in an air atmosphere, and Pt nanoparticles were photo-deposited on the Nb2O5 samples. The surface was analyzed by scanning electron microscope, transmission electron microscope, x-ray photoelectron spectroscopy, and ultraviolet-visible spectrophotometry. Photocatalytic activity of the fabricated materials was studied using methylene blue (MB) decolorization process. An enhanced photocatalytic performance was identified on FN Nb2O5 substrate with Pt deposition.

DOI： 10.1002/cphc.201800769

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Growth of nano-tendril bundles on tungsten with impurity-rich He plasmas Reviewed

Hwangbo Dogyun, Kajita Shin, Ohno Noriyasu, McCarthy Patrick, Bradley James W, Tanaka Hirohiko

NUCLEAR FUSION Vol. 58 ( 9 ) page： 096022 2018.9

Thomson Scattering Measurement of Two Electron Temperature Components in Transition to Detached Plasmas Reviewed

Ohshima Hiroshi, Kajita Shin, Tanaka Hirohiko, Ohno Noriyasu, Van der Meiden Hennie J

PLASMA AND FUSION RESEARCH Vol. 13 page： 1201099 2018.8

Effect of the Nanostructured Layer Thickness on the Dynamics of Cathode Spots on Tungsten Reviewed International coauthorship

S.A. Barengolts, V.G. Mesyats, M. M. Tsventoukh, S.Kajita, D.Hwangbo, N.Ohno

IEEE Transactions on Plasma Science Vol. 46 ( 11 ) page： 4044 - 4050 2018.8

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

IEEE Experimental data on the effect of the thickness of a nanostructured layer present on the surface of a tungsten cathode on its arcing properties have been analyzed. It has been shown that if the nanostructured layer is not completely destroyed as a result of the operation of a cathode spot cell, the spot ``sinks'' in the layer, the spot cells group together, and the trajectory of the spot motion becomes ``entangled.'' To interpret the experimental results, the grouping of arc spot cells was simulated using a random walk model based on the Monte Carlo method into which an attractive force was introduced and assuming that the cell plasma density, i.e., the cell initiation probability, is proportional to 1/r&#x00B2;, where r is the distance between two spot cells. It has been demonstrated that spot cells are entangled, forming a group and moving together when the attractive force between them is strong enough. When this force decreases and the directionality of the cells increases as the cathode spot shifts to a lower thickness region of the nanostructured layer, the velocity of motion of the spot increases and its trace left on the surface becomes narrower.

DOI： 10.1109/TPS.2018.2859953

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

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

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

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

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

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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

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

Web of Science

Scopus

Fuzzy nanostructure growth on precious metals by He plasma irradiation Reviewed

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

Web of Science

Scopus

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

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Papers - OHNO, Noriyasu