Faculty Profiles - OHNO, Noriyasu

Papers - OHNO, Noriyasu

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Deuterium Atomic Density Estimation in Recombining Plasmas Using Self-Absorption Spectroscopy Reviewed

S.Kajita, T.Nishiwaki, N.Ohno, K.Sawada, M.Takagi

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING Vol. 8 ( 1 ) page： 1-6 2013

Observation of Arc Spots Initiated on Nanostructured Tungsten Reviewed

S.Kajita, N.Ohno, S.Takamura

IEEE TRANSACTIONS ON PLASMA SCIENCE Vol. 41 ( 8, Part 2 ) page： 1889-1895 2013

Intermittent transport in edge plasma with a 3-D magnetic geometry in the Large Helical Device Reviewed

H.Tanaka, S.Masuzaki, N.Ohno, T.Morisaki, Y.Tsuji, the LHD Experiment Group

Journal of Nuclear Materials Vol. 438 page： S563-S566 2013

Extension of operation regimes and investigation of three-dimensional currentless plasmas in the Large Helical Device Reviewed

O.Kaneko, H.Yamada, S.Inagaki, M.Jakubowski, S.Kajita, et al.(N.Ohno is the 104th author))

Nucl. Fusion Vol. 53 page： 104015(11 pp) 2013

First-Principles Investigation on Trapping of Multiple Helium Atoms within a Tungsten Monovacancy Reviewed

A.Takayama, A.M.Ito, S.Saito, N.Ohno, H.Nakamura

Jpn. J. Appl. Phys. Vol. 52 page： 01AL023(4 pp) 2013

Effect of resistivity profile on current decay time of initial phase of current quench in neon-gas-puff inducing disruptions of JT-60U Reviewed

S.Kawakami, Y.Shibata, K.Y.Watanabe, N.Ohno, A.Isayama, T.Takizuka, Y.Kawano, M.Okamoto

Physics of Plasmas Vol. 20 page： 112507(6 pp) 2013

Degradation of optical reflectivity of in-vessel mirror materials by helium bombardment Reviewed

S.Kajita, M.Tokitani, T.Saekim N.Ohno, N.Yoshida

J. Nucl. Mater. Vol. 417 page： 838-841 2013

Behavior of Plasma Response Field in Detached Plasma Reviewed International journal

NARUSHIMA Yoshiro, KOBAYASHI Masahiro, AKIYAMA Tsuyoshi, SAKAKIBARA Satoru, MASUZAKI Suguru, ASHIKAWA Naoko, OHNO Noriyasu

Plasma and Fusion Research Vol. 8 ( 0 ) page： 1402058 - 1402058 2013

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：プラズマ・核融合学会

Sustaining a detached plasma is important for the reduction of the heat load on a divertor. The externally controlled methods such as gas puffing in the divertor region, etc. have been studied for maintaining detached plasmas. In the recent LHD experiments, a resonant magnetic perturbation (RMP) is utilized to establish the detached plasma, which is one of the candidates to reduce the divertor heat load. The finite plasma response field has been detected when the RMP is imposed, and its behavior is investigated from the viewpoint of the magnetic island dynamics. A parameter of the phase difference, Δθ (defined as the phase difference between the plasma response field and the RMP), changes from antiphase to in-phase while the plasma transits from the attached to the detached states. Finally, when the Δθ reaches at certain critical value, Δθcrit, the plasma enters the detached state. Since this critical value does not have a dependency on plasma beta and collisionality, Δθcrit seems to be a threshold to establish the detached plasma. From the viewpoint of magnetic island dynamics, the behavior of Δθ approaching in-phase implies the "trend" of island growth. The detached plasma might be established in the case of the tendency for the plasma response field to reinforce the island width.

DOI： 10.1585/pfr.8.1402058

Thermal radiation characteristics and direct evidence of tungsten cooling on the way to nanostructure formation on its surface Reviewed International journal

Takamura S., Miyamoto T., Ohno N.

Journal of Nuclear Materials Vol. 438 ( SUPPL ) 2013

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Nuclear Materials

The physical properties of tungsten with nanostructure on its surface are investigated focusing on the thermal radiation and cooling characteristics. First, direct evidence of substantial W surface cooling has been clearly shown with use of a very thin thermocouple inserted into W target, which solves an uncertainty associated with a radiation thermometer. Second, the above measurements of W surface temperature make it possible to estimate quantitatively the total emissivity from which we may evaluate the radiative power through the Stefan-Boltzmann equation, which is very important for mitigation evaluation of a serious plasma heat load to the plasma-facing component. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnucmat.2013.01.176

Scopus

Preliminary experiments on the vertical stability with helical coils in a small tokamak, HYBTOK-II Reviewed International journal

Hatakeyama S., Shibata Y., Kawakami S., Tsutsui H., Tsuji-Iio S., Shimada R., Ohno N., Akiyama T., Suzuki Y., Watanabe K.

39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics Vol. 1 page： 285 - 288 2012.12

Language：English Publishing type：Research paper (international conference proceedings) Publisher：39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics

In summary, we proposed saddle shaped stellarator system for vertical mode in toka-mak. These preliminary results demonstrate the feasibility of vertical stability, even if only two selected coils which are localized at one side of the torus. However as noted earlier, the experiment were conducted with the circular cross-section tokamak which is stable vertically. Further work is needed to confirm the improvement in the vertical stability in elongated tokamaks. In addition, very large coil current comparable to the plasma current are needed in our system. In order to reduce the current, future work also should focus on optimal configuration of the coils.

Scopus

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

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Papers - OHNO, Noriyasu