Faculty Profiles - OHNO, Noriyasu

Papers - OHNO, Noriyasu

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Blob/Hole Generation in the Divertor Leg of the Large Helical Device Reviewed

H.Tanaka, N.Ohno, Y.Tsuji, S.Kajita, S.Masuzaki, M.Kobayashi, T.Morisaki, A.Komori and the LHD Experimental Group

Plasma and Fusion Research Vol. 7 page： 1402152(6 pp) 2012.11

Fatal Damages due to Breakdown on a Diagnostic Mirror Located outside the Vacuum Vessel in JT-60U Reviewed

S.Kajita, T.Hatae, T.Sakuma, S.Takamura, N.Ohno, K.Itami

Plasma and Fusion Research Vol. 7 page： 2405121(4 pages) 2012.9

Optical properties of nanostructured tungsten in near infrared range Reviewed

S.Kajita, N.Ohno, T.Yokochi, N.Yoshida, R.Yoshihara, S.Takamura, T.Hatae

Plasma Physics and Controlled Fusion Vol. 54 page： 105015(7 pages) 2012.9

Superimposition of Pulses to Steady Arc Discharge in Toroidal Divertor Simulator Reviewed

S.Kajita, T.Uchiyama, N.Ohno

Plasma and Fusion Research Vol. 7 page： 1405100(6 pages) 2012.7

Statistical Analysis of the Spatial Behavior of Plasma Blobs Around the Plasma Column in a Linear Plasma Device Reviewed

H.Tanaka, N.Ohno, Y.Tsuji, K.Okazaki, S.Kajita

Contrib. Plasma Phys. Vol. 52 ( 5-6 ) page： 424 - 428 2012.6

Effect of Externally Applied Resonance Magnetic Perturbation on Current Decay during Tokamak Disruption Reviewed

Y.Kanazawa, Y.Shibata, M.Okamoto, N.Ohno, S.Kajita

Plasma and Fusion Research Vol. 7 page： 1202049(2 pages) 2012.6

Effect of neutral pressure on the He plasma flow measurement in a linear device Reviewed International coauthorship

E.-K.Park, H.-J.Woo, K.-S.Chung, H.Tanaka, S.Kajita, N.Ohno

Current Applied Physics Vol. 12 page： 1479 - 1502 2012.5

Transition in Plasma Fluctuation between Attached and Detached Plasmas Reviewed

K.Okazaki, H.Tanaka, N.Ohno, S.Kajita

Plasma and Fusion Research Vol. 7 page： 1201033(2 pages) 2012.4

Arcing on tungsten subjected to helium and transients: ignition conditions and erosion rates Reviewed International journal

S.Kajita, N.Ohno, N.Yoshida, R.Yoshihara, S.Takamura

PLASMA PHYSICS AND CONTROLLED FUSION Vol. 54 ( 3 ) 2012.2

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

Arcing is a long standing plasma-surface interaction issue in nuclear fusion research, and the issue has been revived recently from new points of view. In this study, arcing under fusion relevant conditions is demonstrated in a linear plasma device using a pulsed laser to mimic the transient heat load. Ignition conditions of arcing were investigated systematically by changing the laser power, plasma conditions, surface nature and so on. Moreover, the cross-sectional view of arc trail was observed by transmission electron microscope, and the erosion of nanostructured tungsten due to arcing was estimated. It was found that more than half of the nanostructured tungsten still remained after an arc spot run on the nanostructure.

DOI： 10.1088/0741-3335/54/3/035009

Web of Science

TEM analysis of high temperature annealed W nanostructure surfaces Reviewed International journal

Shin Kajita, Naoaki Yoshida, Reiko Yoshihara, Noriyasu Ohno, Takanori Yokochi, Masayuki Tokitani, Shuichi Takamura

JOURNAL OF NUCLEAR MATERIALS Vol. 421 ( 1-3 ) page： 22 - 27 2012.2

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

Helium plasma irradiation and electron heating experiments were conducted using tungsten in the divertor simulator NAGDIS-II. Helium plasma irradiation to tungsten led to the formation of nanostructures on the surface, while the nanostructures were annihilated after the potential of the specimen was changed to positive for several 10 min so that electrons irradiated the sample without ion irradiation. The specimens were analyzed in detail by transmission electron microscope with the help of focused ion beam technique. It is revealed that the helium nano-bubbles still remained even after the nanostructures were disappeared from the surface. Porosity of the nanostructured tungsten was measured from the TEM images. (c) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnucmat.2011.11.044

Web of Science

Anisotropic Graphite Erosion in Low-Temperature and high-Density Deuterium Plasma Reviewed

M.Teraoka, N.Ohno, S.Kajita, T.Nishiwaki, A.M.Ito, H.Nakamura

Jpn. J. Appl. Phys. Vol. 51 page： 01AB03 (5pp) 2012.1

Near Infrared Radiation from Heated Nanostructured Tungsten Reviewed

S.Kajita, T.Yokochi, N.Ohno, T.Kumano

Jpn. J. Appl. Phys. Vol. 51 page： 01AJ03 (5pp) 2012.1

Measurement of ion and electron temperatures in plasma blobs by using an improved ion sensitive probe system and statistical analysis methods Reviewed International journal Open Access

K. Okazaki, H. Tanaka, H. Tanaka, N. Ohno, N. Ezumi, Y. Tsuji, S. Kajita

Review of Scientific Instruments Vol. 83 2012.1

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

We have measured ion temperature as well as electron temperature in plasma blobs observed in a linear plasma device by using an improved ion sensitive probe. Current-voltage characteristics of the ion sensitive probe inside and outside plasma blobs were re-constructed with a conditional sampling method. It is clearly found that both ion and electron temperatures in plasma blobs decrease more slowly in a cross-field direction than those in a bulk plasma without plasma blobs. © 2012 American Institute of Physics.

DOI： 10.1063/1.3681778

Scopus

Electric Field at a Plasma-Facing Wall for a Two-Temperature Electron Distribution Reviewed

Y.Tomita, G.Kawamura, M.Ueno, N.Ohno, Z.H.Huang, Y.D.Pan, L.W.Yan

Contrib. Plasma Phys. Vol. 52 ( 5-6 ) page： 484-489 2012

Thermionic Energy Converter System Using Heat Flux in Divertor Region Reviewed

D.Oikawa, N.Ohno, S.Kajita, M.Takagi, S.Masuzaki, M.Tokitani, K.Asano

Plasma and Fusion Research Vol. 7 page： 1405050(8 pages) 2012

Conditions for the Release of a Metallic Dust Particle from a Plasma-Facing Wall Reviewed

M.Ueno, N.Ohno, Y.Tomita, G.Kawamura

Contrib. Plasma Phys. Vol. 52 ( 5-6 ) page： 478-483 2012

Effects of fibre-form nanostructures on particle emissions from a tungsten surface in plasmas Reviewed

S.Takamura, T.Miyamoto, N.Ohno

Nuclear Fusion Vol. 52 page： 123001(8 pages) 2012

Validation of the current decay model in the initial phase of current quench in high disruptive discharges of JT-60U Reviewed International journal

Shibata Y., Watanabe K., Ohno N., Okamoto M., Isayama A., Kurihara K., Oyama N., Nakano T., Kawano Y., Sugihara M.

38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts Vol. 35 2 page： 1628 - 1631 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts

The validation of current decay model during the current quench was investigated in high (3p disruptive discharges on JT-60U. It is experimentally confirmed that the electron temperature does not play an important role in the determination of the current decay time in the initial phase of current quench and that values obtained from L/R model are two orders of magnitude larger than the experimental current decay time. The current decay time predicted by the modified L/R model, in which the time derivative of plasma inductance is taken into account, is in fairly good agreement with the experimental data. In future work, we need to perform the MHD equilibrium code for free-boundary condition such as DINA [5] and TSC [6] code under the axisymmetric assumption in order to clear up the determination mechanism of time derivative of plasma inductance.

Scopus

Recent progress of tungsten R&D for fusion application in Japan Reviewed International journal

Ueda Y., Lee H.T., Ohno N., Kajita S., Kimura A., Kasada R., Nagasaka T., Hatano Y., Hasegawa A., Kurishita H., Oya Y.

Physica Scripta T Vol. T145 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Scripta T

The status of ongoing research projects of tungsten R&D in Japan is summarized in this paper. For tungsten material development, a new improved fabrication technique, the so-called superplasticity-based microstructural modification, is described. This technique successfully improved fracture strength and ductility at room temperature. Recent results on vacuum plasma spray W coating and W brazing on ferritic steels and vanadium alloys are explained. Feasibility of these techniques for the manufacture of the blanket is successfully demonstrated. The latest findings on the effect of neutron damage in tungsten on T retention and on the change in mechanical and electrical properties are described. Retention characteristics for neutron-damaged W were different compared to those for ion-damaged W. Upon neutron irradiation, tungsten alloys containing transmutation elements of W (Re and Os) show changes in properties that are different compared with those shown by pure W. The effects of mixed plasma exposure (D/He/C) are described. Both D/He and D/C mixed ion irradiations significantly affect ion-driven permeation in W. He bubble dynamics play a key role in nano-structure formation on the W surface. © 2011 The Royal Swedish Academy of Sciences.

DOI： 10.1088/0031-8949/2011/T145/014029

Scopus

Deuterium retention in Fe <inf>2</inf>O <inf>3</inf> under low-energy deuterium-plasma exposure Reviewed International journal

Matsunami N., Sogawa T., Sakuma Y., Ohno N., Tokitani M., Masuzaki S.

Physica Scripta T Vol. T145 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Scripta T

Stainless steel (SUS) is used as the structure material in nuclear fusion devices. Heating and O 2 plasma discharge are considered for the removal of tritium. Oxide layer growth is anticipated on heating SUS at a high temperature in low-pressure residual O 2 gas. When O 2 plasma discharge is performed, oxygen plasma reaches the structure material and iron oxides such as Fe 2O 3 are formed. Thus, a knowledge of the retention behavior of hydrogen isotopes or deuterium (D) in the oxide layers is important in designing the devices. We investigated D retention in Fe 2O 3 films and the influence of Fe 2O 3 crystal structure on D retention and found that D retention in γ-Fe 2O 3 (cubic-maghemite) is larger than that in α-Fe 2O 3 (hexagonal-hematite). The results for Fe 2O 3 are compared with those for SUS and Fe. © 2011 The Royal Swedish Academy of Sciences.

DOI： 10.1088/0031-8949/2011/T145/014042

Scopus

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Papers - OHNO, Noriyasu