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Journal Articles

Eddy current-adjusted plasma shape reconstruction by Cauchy condition surface method on QUEST

Nakamura, Kazuo*; Jiang, Y.*; Liu, X.*; Mitarai, Osamu*; Kurihara, Kenichi; Kawamata, Yoichi; Sueoka, Michiharu; Hasegawa, Makoto*; Tokunaga, Kazutoshi*; Zushi, Hideki*; et al.

Fusion Engineering and Design, 86(6-8), p.1080 - 1084, 2011/10

 Times Cited Count:4 Percentile:34.66(Nuclear Science & Technology)

Journal Articles

Application of tritium tracer techniques to observation of hydrogen on surface and in bulk of F82H

Otsuka, Teppei*; Tanabe, Tetsuo*; Tokunaga, Kazutoshi*; Yoshida, Naoaki*; Ezato, Koichiro; Suzuki, Satoshi; Akiba, Masato

Journal of Nuclear Materials, 417(1-3), p.1135 - 1138, 2011/10

 Times Cited Count:2 Percentile:19.41(Materials Science, Multidisciplinary)

Journal Articles

Hydrogen up-take in noble gas implanted W

Nagata, Shinji*; Yamamoto, Shunya; Tokunaga, Kazutoshi*; Tsuchiya, Bun*; To, Kentaro*; Shikama, Tatsuo*

Nuclear Instruments and Methods in Physics Research B, 242(1-2), p.553 - 556, 2006/01

 Times Cited Count:7 Percentile:48.31(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Present research status on divertor and plasma facing components for fusion power plants

Suzuki, Satoshi; Ueda, Yoshio*; Tokunaga, Kazutoshi*; Sato, Kazuyoshi; Akiba, Masato

Fusion Science and Technology, 44(1), p.41 - 48, 2003/07

 Times Cited Count:26 Percentile:84.5(Nuclear Science & Technology)

no abstracts in English

Oral presentation

Effect of hydrogen and helium irradiation on optical property of tungsten

Tokunaga, Kazutoshi*; Ezato, Koichiro; Suzuki, Satoshi; Akiba, Masato; Fujiwara, Tadashi*; Yoshida, Naoaki*

no journal, , 

Polycrystalline tungsten samples have been irradiated by 19 keV pulsed hydrogen and helium beam up to 1$$times$$10$$^{24}$$/m$$^{2}$$. Optical reflectivity has been measured with an ultraviolet-visible and near-infrared spectrophotometer, and a Fourier transform-infrared (FT-IR) spectrometer for the wave length between 190 - 2400 nm, 1.4 - 20 $$mu$$m, respectively. In addition, optical constants have been calculated by results measured using a spectroscopic ellipsometer. Surface morphology has been also examined with a scanning electron microscope. Loss of metallic gloss and remarkable reduction of reflectivity (190-2400 nm) occurs by the hydrogen and helium irradiation of $$sim$$1022 He$$^{+}$$/m$$^{2}$$. In particular, helium beam irradiation at a peak temperature 2600 $$^{circ}$$C causes remarkably decrease of the reflectivity due to fine uneven morphology and bubble formation near-surface. The reduction of the reflectivity is considered to be mainly due to the porous structure with nano-scale hydrogen and helium bubbles.

Oral presentation

Irradiation experiments of high heat flux hydrogen and helium dual beams on tungsten materials

Tokunaga, Kazutoshi*; Fujiwara, Tadashi*; Ezato, Koichiro; Suzuki, Satoshi; Akiba, Masato; Kurishita, Hiroaki*; Yoshida, Naoaki*

no journal, , 

no abstracts in English

Oral presentation

Characteristics of SVD in ST plasma shape reproduction method based on CCS

Nakamura, Kazuo*; Matsufuji, Shinji*; Tomoda, Seiji*; Wang, F.*; Mitarai, Osamu*; Kurihara, Kenichi; Kawamata, Yoichi; Sueoka, Michiharu; Hasegawa, Makoto*; Tokunaga, Kazutoshi*; et al.

no journal, , 

no abstracts in English

Oral presentation

Eddy current effect on plasma shape reconstruction based on CCS method in QUEST

Nakamura, Kazuo*; Yi, J.*; Liu, X.*; Mitarai, Osamu*; Kurihara, Kenichi; Kawamata, Yoichi; Sueoka, Michiharu; Hasegawa, Makoto*; Tokunaga, Kazutoshi*; Zushi, Hideki*; et al.

no journal, , 

no abstracts in English

Oral presentation

Real time reconstruction of spherical tokamak plasma shape by CCS method with eddy current in QUEST

Yi, J.*; Nakamura, Kazuo*; Liu, X.*; Mitarai, Osamu*; Kurihara, Kenichi; Kawamata, Yoichi; Sueoka, Michiharu; Hasegawa, Makoto*; Tokunaga, Kazutoshi*; Zushi, Hideki*; et al.

no journal, , 

no abstracts in English

Oral presentation

Multiple irradiation experiment of tungsten materials by negative hydrogen ion beam, 1; Study of beam target materials

Hirano, Koichiro; Fukuda, Makoto*; Ezato, Koichiro*; Tokunaga, Kazutoshi*

no journal, , 

The beam targets of the J-PARC linac are multiply irradiated by hydrogen negative ion beams with beam energy of 3 MeV. The purpose of this study is to clarify the pulsed heat load conditions that can withstand multiple irradiations when beam targets made of tungsten materials are used. Using an off-line beam test-stand with a 3 MeV hydrogen negative ion beam, multiple irradiation tests were conducted on tungsten materials for ITER, in which temperature changes of heating (3200 degree) and cooling (160 degree) were repeatedly given at a period of 5 Hz. This paper reports on the surface observation of the tungsten materials and the partial pressure measurements by a quadrupole mass spectrometer.

Oral presentation

Multiple irradiation experiment of tungsten materials by negative hydrogen ion beam, 2; Evaluation as material for ITER divertor

Fukuda, Makoto*; Hirano, Koichiro; Tokunaga, Kazutoshi*; Ezato, Koichiro*

no journal, , 

Tungsten which is used as a plasma-facing material for ITER divertor is expected to receive heat flux under various conditions during ITER operation. Therefore, it is necessary to understand the modification of tungsten surface under various heat load conditions. In this work, as part of the investigation of the repeated short pulse heat load effect on tungsten, the effect of multiple irradiation (3MeV, 5Hz) with a negative hydrogen ion beam was evaluated. As a result, unevenness and cracks were observed on the surface after irradiation, and different surface modification behavior was observed compared with previous experiment which performed with almost constant heat load (10s On and 20-30 s Off as one cycle).

Oral presentation

Multiple irradiation experiment of tungsten materials by negative hydrogen ion beam, 3; Observation of material degradation by multiple irradiation

Tokunaga, Kazutoshi*; Nomiyama, Yukino*; Fukuda, Makoto*; Ezato, Koichiro*; Hirano, Koichiro

no journal, , 

The surface modification of tungsten materials exposed by multiple irradiations of a negative hydrogen ion beam is examined to investigate the influence of the repeated short pulse heat loading. Grid-like cracks are formed on the sample surfaces which the surface is perpendicular to the rolling direction. On the other hand, ellipsoidal cracks are formed on the sample surfaces which the surface is parallel to the rolling direction. These results show crack formation is different depending on the orientation of grain boundaries. The surface modification by plastic formation due to the repeated heat loading in the center area surrounded by the cracks is observed. Furthermore, in the case of high heat loading conditions, a number of cone-like protuberances are melted and resolidified, and deep cracks are formed in the vicinity. The peculiar surface such as the deep cracks and the cone-like protuberances are formed.

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