Faculty Profiles - OHNO, Noriyasu

Field Emission From Nanostructured Tendril Bundles Reviewed International coauthorship

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

IEEE TRANSACTIONS ON PLASMA SCIENCE Vol. 47 ( 11 ) page： 5186 - 5190 2019.10

Kinetics of deuterium penetration into neutron-irradiated tungsten under exposure to high flux deuterium plasma Reviewed Open Access

M. Yajima, Y. Hatano, N. Ohno, T. Kuwabara, T. Toyama, M. Takagi, K. Suzuki

Nuclear Materials and Energy Vol. 21 page： 100699 2019.8

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

© 2019 The Authors The objective of this study is to investigate the effects of neutron (n) irradiation on hydrogen isotope transport in tungsten (W). W samples were irradiated with neutrons in a fission reactor and then exposed to high flux deuterium (D) plasma at 563 K in a linear plasma device. The fraction of D release increased with increasing exposure time. In addition, the D retention in n-irradiated W increased in proportion to the square root of the plasma exposure time. These observations were explained by increase in the penetration depth of D with filling up displacement damages acting as strong trapping sites.

DOI： 10.1016/j.nme.2019.100699

Application of Ion Sensitive Probe to High Density Plasmas in Magnum-PSI Reviewed International coauthorship Open Access

Y.Hayashi, N.Ohno, H.van der Meiden, J.Scholten, S.Kajita, J.van der Berg, R.Perillo, J.Vernimmen, T.Moragan

PLASMA AND FUSION RESEARCH Vol. 14 page： 1202135(3 pp) 2019.7

Spatial and temporal measurement of recombining detached plasmas by laser Thomson scattering Reviewed Open Access

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

PLASMA SOURCES SCIENCE & TECHNOLOGY Vol. 28 page： 105015 (9pp) 2019.7

Photocatalytic decomposition of ethylene using He plasma induced nano-TiO<inf>2</inf> Reviewed Open Access

S.Kajita, Y.Tomita, E.Yasunaga, T.Yoshida, K.Miyaguchi, H.Tanaka, N.Ohno

Japanese Journal of Applied Physics Vol. 58 page： 070903(4 pp) 2019.6

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

© 2019 The Japan Society of Applied Physics. Ethylene decomposition via photocatalytic reaction using ultra-violet light was performed using an oxidized titanium (Ti) sheet and/or thin film samples fabricated by helium (He) plasmas treatments. We prepared nanostructured Ti samples formed by He plasma irradiation and additional thin film deposited samples using radio frequency magnetron sputtering. The samples prepared in this study had a slightly lower photocatalytic activity compared to the thin film deposited on tungsten nanostructure samples previously reported; the anatase formation was solely identified on Ti sheet samples and is hopeful for further improvement of photocatalytic activity of plasma treated titania.

DOI： 10.7567/1347-4065/ab2830

Fabrication of a nanostructured TiO<inf>2</inf> photocatalyst using He plasma-irradiated tungsten and ethylene gas decomposition Reviewed

Y.Tomita, S.Kajita, E.Yasunaga, T.Yoshida, N.Ohno, H.Tanaka

Japanese Journal of Applied Physics Vol. 58 ( SE ) page： SEEG01(6 pp) 2019.5

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

© 2019 The Japan Society of Applied Physics. Decomposition of ethylene gas by a photocatalyst is an environmentally friendly and sustainable process. We fabricated titanium dioxide thin films deposited on nanostructured tungsten substrates formed by exposure to helium plasma and evaluated their photocatalytic performance. The nanostructures were maintained even after sputtering and annealing, and the proportion of tungsten inside the thin film increased with increasing oxidation temperature. The photocatalytic activity was improved due to formation of the nanostructure.

DOI： 10.7567/1347-4065/ab09c8

Investigation of recombination front region in detached plasmas in a linear divertor plasma simulator Reviewed International coauthorship Open Access

N.Ohno, M.Seki, H.Ohshima, H.Tanaka, S.Kajita, Y.Hayashi, H.Natsume, H.Takano, I.Saeki, M.Yoshikawa, H.van der Meiden

Nuclear Materials and Energy Vol. 19 page： 458 - 462 2019.5

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

We have investigated detailed plasma structure around the recombination front region (RFR), where volume electron-ion recombination (EIR) strongly occurs in detached plasmas, by using two-dimensional (2D) movable probe system as well as laser Thomson scattering diagnostics. The 2D distribution of electron density, electron temperature, and plasma potential around the RFR, has been revealed for the first time. The spatial distribution of the particle loss rate due to EIR estimated from electron temperature and electron density profiles indicated that the three-dimensional structure of the RFR adopts a cone structure. Furthermore, in the peripheral region of the RFR, the radial profile of the electron density was widened locally with increasing cross-field transport caused by plasma fluctuation. From the heat transport analysis of electrons, it was found that the thermal relaxation process between electrons and ions is important for the cooling of electrons, and that the convection of electrons regulates electron heat transport near the RFR.

DOI： 10.1016/j.nme.2019.03.010

Generation of Spiral Shape Nitrogen Recombining Plasma for Atomic Nitrogen Source Reviewed

K. Asaoka, N. Ohno, Y. Hayashi, S. Kajita, and H. Tanaka

Plasma and Fusion Research Vol. 14 page： 3401069(4 pp) 2019.4

Characterization of He induced nanostructures using SEM image analysis Reviewed Open Access

H.Tanaka, S.Kajita, N.Ohno

Plasma and Fusion Research Vol. 14 ( Specialissue2 ) page： 3402049(6 pp) 2019.4

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

© 2019 The Japan Society of Plasma Science and Nuclear Fusion Research. Helium induced nanostructures on tungsten were characterized by applying basic statistical analysis techniques to scanning electron microscope (SEM) images. As the analysis targets, pinhole- and fuzz-dominant surfaces irradiated with different ion fluences were employed. Although two-dimensional Fourier analysis of the normalized brightness of SEM images clarified several characteristic features, their differences are small to distinguish the dominant nanostructures. On the other hand, probability density functions (PDFs) of the normalized brightness indicate that hole- and fuzz-dominant surfaces have long tail and Gaussian-like shape, respectively. By using several indexes with considering the black and white saturation, it was found that kurtosis and Kullback- Leibler divergence could provide reasonable judgement as the characterization index.

DOI： 10.1585/pfr.14.3402049