Faculty Profiles - OHNO, Noriyasu

Papers - OHNO, Noriyasu

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Measurement of Poloidal Flow Profiles Using a Mach Probe Array in HYBTOK-II Tokamak with RMP Fields Reviewed

Okamoto Masaaki, Sakakibara Satoru, Yoshimoto Naoya, Ohno Takuya, Ohno Noriyasu

PLASMA AND FUSION RESEARCH Vol. 12 page： 1202027 2017.6

Observations of sustained phase shifted magnetic islands from externally imposed m/n=1/1 RMP in LHD Reviewed International coauthorship

Narushima Y., Sakakibara S., Suzuki Y., Watanabe K. Y., Ohdachi S., Takemura Y., Yoshinuma M., Ida K., Castejon F., Lopez-Bruna D., Hegna C. C., Kobayashi M., Tanaka H., Akiyama T., Ohno N.

NUCLEAR FUSION Vol. 57 ( 7 ) page： 076024 2017.5

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

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

Nuclear Materials and Energy Vol. 12 page： 1004-1009 2017.5

Increase in the energy absorption of pulsed plasma by the formation of tungsten nanostructure Reviewed

D. Sato, N. Ohno, F. Domon, S. Kajita, Y. Kikuchi, I. Sakuma

Nuclear Fusion Vol. 57 ( 6 ) page： 066028(8 pp) 2017.4

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

© 2017 IAEA, Vienna. The synergistic effects of steady-state and pulsed plasma irradiation to material have been investigated in the device NAGDIS-PG (Nagoya DIvertor Simulator with Plasma Gun). The duration of the pulsed plasma was ∼0.25 ms. To investigate the pulsed plasma heat load on the materials, we developed a temperature measurement system using radiation from the sample in a high time resolution. The heat deposited in response to the transient plasma on a tungsten surface was revealed by using this system. When the nanostructures were formed by helium plasma irradiation, the temperature increase on the bulk sample was enhanced. The result suggested that the amount of absorbed energy on the surface was increased by the formation of nanostructures. The possible mechanisms causing the phenomena are discussed with the calculation of a sample temperature in response to the transient heat load.

DOI： 10.1088/1741-4326/aa67ad

Web of Science

Scopus

Tailoring of fuzzy nanostructures on porous tungsten skeleton by helium plasma irradiation Reviewed

Shin Kajita, Hirohiko Tanaka, Noriyasu Ohno

Japanese Journal of Applied Physics Vol. 56 ( 3 ) page： 030303(4 pp) 2017.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Japan Society of Applied Physics

Porous tungsten skeleton, which was fabricated by sintering of tungsten powder, was exposed to helium plasmas, and the fuzzy nanostructures were tailored on the surface. The hemispherical optical reflectance of the samples was measured at the wavelength of 633 nm. It was shown that the optical reflectance of the porous tungsten skeleton was lower than that of flat tungsten samples. The minimum reflectance was &gt
0.4%, suggesting that the darkest metallic material was fabricated. The advantage of the porous tungsten skeleton with nanostructures for optical application is discussed.

DOI： 10.7567/JJAP.56.030303

Web of Science

Scopus

Plasma detachment in linear devices Reviewed

Ohno N.

PLASMA PHYSICS AND CONTROLLED FUSION Vol. 59 ( 3 ) page： 034007(9 pp) 2017.3

Localized density fluctuation in the downstream of detached plasma Reviewed

Kohei Takeyama, Noriyasu Ohno, Masayuki Yoshikawa, Hirohiko Tanaka, Shin Kajita

Plasma and Fusion Research Vol. 12 ( 1 ) page： 1202007 2017.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Japan Society of Plasma Science and Nuclear Fusion Research

The density fluctuation was measured with a 70-GHz microwave interferometry system in the linear divertor plasma simulator NAGDIS-II while changing from the attached to the detached states. In the detached plasma, a large amplitude fluctuation of ≤ 10 kHz appeared in the peripheral region. The fluctuation has a maximum value at the neutral gas pressure of 30 - 34 mTorr. Further, the measurement of the light emission associated with the plasma recombination indicates that the large amplitude fluctuation is located at just downstream of the recombination front, in which the recombination process is the most enhanced.

DOI： 10.1585/pfr.12.1202007

Web of Science

Scopus

Transverse motion of a plasma column in a sheet plasma Reviewed

Takuya Onda, Shin Kajita, Takaaki Iijima, Akira Tonegawa, Noriyasu Ohno, Hirohiko Tanaka

CONTRIBUTIONS TO PLASMA PHYSICS Vol. 57 ( 2 ) page： 87 - 93 2017.2

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

In this paper, we show the dynamic behaviors of a sheet plasma and the corresponding release of blob-like plasmas to the periphery of the sheet based on observation with a high-speed camera. We found that the plasma column moves in a transverse direction reciprocally when injecting a small amount of Ar gas to the He plasma from the plasma source region. The motion continued periodically at a frequency of similar to 5 kHz. The frequency of the plasma column motion decreased with increasing Ar gas flow rate and increasing magnetic field. The mechanism of the transverse motion is discussed. Furthermore, in response to the reciprocating motion, release of a blob-like plasma was observed. The differences in the behavior of the released plasma compared with the other linear devices are discussed.

DOI： 10.1002/ctpp.201500142

Web of Science

In Situ TEM Observation of Helium Bubbles Collapsing on Nanostructured Tungsten during Annealing Reviewed

M. Yajima, N. Yoshida, S. Kajita, and N. Ohno

Plasma and Fusion Research Vol. 11 page： 1206125 2016.12

Measurement of heat diffusion across fuzzy tungsten layer Reviewed

S.Kajita, T.Yagi, K.Kobayashi, M.Tokitani, N.Ohno

Results in Physics Vol. 6 page： 877-878 2016.11

Enhancement of photocatalytic activity of TiO2 by plasma irradiation Reviewed

S.Kajita, T.Yoshida, N.Ohno, T.Ishida, D.Kitaoka

Japanese Journal of Applied Physics Vol. 55 page： 106202(5 pp) 2016.9

Plasma detachment study of high density helium plasmas in the Pilot-PSI device Reviewed

Y.Hayashi, K.Jesko, H.J.van der Meiden, J.W.M.Vernimmen, T.W.Morgan, N.Ohno, S.Kajita, M.Yoshikawa, S.Masuzaki

Nuclear Fusion Vol. 56 page： 126006(13 pp) 2016.9

Fuzzy nanostructure growth on Ta/Fe by He plasma irradiation Reviewed

S.Kajita, T.Ishida, N.Ohno, D.Hwangbo, T.Yoshida

Scientific Reports Vol. 6 page： 30380 2016.7

Statistical Analysis of Particle Flux Flowing into the End-Target in between Atached and Detached Sttes in the Linear Divertor Plasma Simulator NAGDIS-II Reviewed

H.Tanaka, N.Ohno, T.Onda, K.Takeyama, S.Kajita, T.Kuwabara, Y.Tsuji

Contrib. Plasma Phys. Vol. 56 ( 6-8 ) page： 723-728 2016.6

Measurement of thermophysical property of plasma forming tungsten nanofiber layer Reviewed

S.Kajita, T.Yagi, K.Kobayashi, M.Tokitani, N.Ohno

Japanese Journal of Applied Physics Vol. 55 page： 056203(5 pp) 2016.4

Dynamics of three-dimensional radiative structures during RMP assisted detached plasmas on the large helical device and its comparison with EMC3-EIRENE modeling Reviewed International coauthorship

Shwetang N. Pandya, Byron J. Peterson, Masahiro Kobayashi, Katsumi Ida, Kiyofumi Mukai, Ryuichi Sano, Junichi Miyazawa, Hirohiko Tanaka, Suguru Masuzaki, Tsuyoshi Akiyama, Gen Motojima, Noriyasu Ohno

NUCLEAR FUSION Vol. 56 ( 4 ) page： 046002 2016.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The resonant magnetic perturbation (RMP) island introduced in the stochastic edge of the large helical device (LHD) plasma plays an important role in the stabilization of the plasma detachment (Kobayashi et al 2013 Nucl. Fusion 53 093032). The plasma enters in the sustained detachment phase in the presence of an RMP once the line averaged density exceeds a critical value with a given input power. During detachment the enhanced radiation from the stochastic edge of the LHD undergoes several spatiotemporal changes which are studied quantitatively by an infrared imaging video bolometer (IRVB) diagnostic. The experimental results are compared qualitatively and quantitatively with the radiation predicted by the 3D transport simulation with fluid model, EMC3-EIRENE. A fair amount of qualitative agreement, before and after the detachment, is reported. The issue of overestimated radiation from the model is addressed by changing the free parameters in the EMC3-EIRENE code till the total radiation and the radiation profiles match closely, within a factor of two with the experimental observations. A better quantitative match between the model and the experiment is achieved at higher cross-field impurity diffusion coefficient and lower sputtering coefficient after the detachment. In this article a comparison, the first of its kind, is established between the quantified radiation from the experiments and the synthetic image obtained from the simulation code. This exercise is aimed towards validating the model assumptions against the experimentally measured radiation.

DOI： 10.1088/0029-5515/56/4/046002

Web of Science

Scopus

Strong Reduction of Ion Flux to a Target Plate in a Magnetically Contracting Detached Plasma Reviewed

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

Plasma and Fusion Research: Rapid Communications Vol. 11 page： 1202005(2 pp) 2016.2

Plasma flow in peripheral region of detached plasma in linear plasma device Reviewed

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

Physics of Plasmas Vol. 23 page： 012511(7 pp) 2016.1

Arc tracks on nanostructured surfaces after microbreakdowns Reviewed

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

Journal of Physics:Conference Series Vol. 748 page： 012012(6 pp) 2016

Detailed Analysis of Plasma Resistivity in Detached Recombining Plasmas Reviewed

H.Nishikata, Y.Hayashi, N.Ohno, S.Kajita, T.Kuwabara

Contrib. Plasma Phys. Vol. 56 ( 6-8 ) page： 717-722 2016

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Papers - OHNO, Noriyasu