Faculty Profiles - OHNO, Noriyasu

Analysis of indefinite divertor footprint with proper orthogonal decomposition in hydrogen/deuterium plasmas in LHD Reviewed Open Access

H.Tanaka, S.Masuzaki, G.Kawamura, M.Kobayashi, Y.Suzuki, T.Morisaki, N.Ohno LHD Experimental Group

Nuclear Materials and Energy Vol. 19 page： 378 - 383 2019.3

Increased energy absorption into W due to the metal deposited layer from an ELM-like pulsed plasma Reviewed Open Access

T.Nakamori, N.Ohno, H.Tanaka, S.Kajita, Y.Kikuchi, T.Akiyama

Plasma and Fusion Research Vol. 14 page： 1401051(5 pp) 2019.3

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

© 2019 The Japan Society of Plasma Science and Nuclear Fusion Research. It is important in divertor physics research to investigate thermal response process of beryllium deposited tungsten to high transient heat load such as ELMs. We investigated the heat load on aluminum-coated tungsten by comparing the measured back surface temperature and calculation results of the one-dimensional heat conduction equation. When the plasma power was low enough so that the evaporation did not occur sufficiently, the heat load on the aluminum-coated tungsten was higher than the virgin tungsten. It was caused by the reduction in the energy reflection coefficient due to the formation of aluminum layer. The results suggested that the beryllium deposited layer adversely affects the heat load on the divertor plate when the heat load was not high such as Grassy-ELM.

DOI： 10.1585/pfr.14.1401051

Double-probe measurement in recombining plasma using NAGDIS-II Reviewed Open Access

Y. Hayashi, H. Nishikata, N. Ohno, S. Kajita, H. Tanaka, H. Ohshima, M. Seki

Contributions to Plasma Physics Vol. 59 ( 7 ) page： e201800088 2019.2

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

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim We have studied the validity of the double-probe method in recombining plasmas. Electron temperature (Te) measured with a double probe was quantitatively evaluated by taking into account the influences of plasma potential fluctuation, plasma resistivity, and electron density fluctuation on the current–voltage characteristics. Differential potential fluctuation and plasma resistivity between two electrodes have a minor effect on Te especially when the inter-distance is small (typically 1 mm). Scattering of measured Te due to the density fluctuation was sufficiently suppressed by making the data acquisition time long (typically 4 s) and taking the average. There is a good agreement between Te measured with the optimized double-probe method and that with laser Thomson scattering diagnostics.

DOI： 10.1002/ctpp.201800088

Development of Thomson scattering measurement system for Upstream plasmas in the NAGDIS-II device Reviewed Open Access

H.Takano, H.Ohshima, S.Kajita, H.Tanaka, N.Ohno

Plasma and Fusion Research Vol. 14 ( Specialissue1 ) page： 2405031(4 pp) 2019.2

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

© 2019 The Japan Society of Plasma Science and Nuclear Fusion Research. A new laser Thomson scattering (LTS) measurement system in the upstream region of the linear plasma device NAGDIS-II is established in addition to the recently introduced LTS in the downstream. Further, horizontal distributions of the electron temperature and electron density were compared with those obtained from the Langmuir probe, indicating plasma disturbance due to the insertion of the probe head. We discuss the variation of the electron energy distribution function at upstream and downstream in the recombining plasma.

DOI： 10.1585/pfr.14.2405031

Growth of membrane nanostructures on W co-deposition layer Reviewed Open Access

S. Kajita, N. Yoshida, S. Kawaguchi, H. Tanaka, N. Ohno, D. Nagata, M. Tokitani

Nuclear Materials and Energy Vol. 18 page： 339 - 344 2019.2

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

© 2019 The Authors Large-scale mm thick fiberform nanostructures are grown when materials are subjected to high flux helium ions with tungsten particles (ions and neutrals) precipitation. Observations of the large-scale fiberform nanostructures (LFNs) were conducted by scanning electron microscope (SEM) and transmission electron microscope (TEM) analyses. In particular, this study focuses on membrane nanostructures. Membranes that contain He bubbles were always observed when LFNs covered the surface. We discuss the growth process of the membrane structures based on detailed observations.

DOI： 10.1016/j.nme.2019.02.004

Spatiotemporal Structure of Hα Emission from the Detached Plasma in GAMMA 10/PDX Reviewed Open Access

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: Regular Articles Vol. 14 page： 2402036(5 pp) 2019.2

Growth process of nano-tendril bundles with sputtered tungsten Reviewed Open Access

D. Hwangbo, S. Kajita, H. Tanaka, and N. Ohno

Nuclear Materials and Energy Vol. 18 page： 250 - 257 2019.1

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

© 2019 The Authors Nano-tendril bundles (NTBs) were generated in DC He plasma with impurity gas-seeding (Ne and N 2 ) under sputtering-dominated conditions. NTB morphologies were characterized using the net erosion yield of samples. NTBs’ height and area were analyzed and ion fluence dependence was discussed. For both impurities, the number of NTBs increased steadily with increasing the fluence. It was revealed that NTB can be generated newly and continuously regardless of ion fluence. Surface observations suggested that micro-protrusions can evolve into NTBs. The effect of re-deposition of W was discussed based on SEM observations. Line-of-sight deposition seemed to play a key role of W feeder to enable NTBs to grow greater.

DOI： 10.1016/j.nme.2019.01.008

Proton scattering from tungsten fuzz

Multipoint measurements employing a microwave interferometer and a Langmuir probe in the detached linear plasma Reviewed Open Access

H. Natsume, H. Tanaka, S. Kajita, M. Yoshikawa, M. Seki, H. Ohshima, and N. Ohno

AIP ADVANCES Vol. 9 page： 015016 (6pp) 2019.1

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

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 Open Access

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

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

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

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 Open Access

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 Open Access

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