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Journal Articles

Overview of plasma-material interaction experiments on EAST employing MAPES

Ding, F.*; Luo, G.-N.*; Pitts, R.*; Litnovsky, A.*; Gong, X.*; Ding, R.*; Mao, H.*; Zhou, H.*; Wampler, W. R.*; Stangeby, P. C.*; et al.

Journal of Nuclear Materials, 455(1-3), p.710 - 716, 2014/12

 Times Cited Count:20 Percentile:8.06(Materials Science, Multidisciplinary)

Journal Articles

Investigation of carbon dust accumulation in the JT-60U tokamak vacuum vessel

Asakura, Nobuyuki; Hayashi, Takao; Ashikawa, Naoko*; Fukumoto, Masakatsu

Journal of Nuclear Materials, 438, p.S659 - S663, 2013/07

 Times Cited Count:1 Percentile:86.44(Materials Science, Multidisciplinary)

Dust generated by the plasma-wall interaction is a potential source of the tritium retention in a fusion reactor. Dust samples were collected at 3, 5 and 3 different toroidal locations of the first wall, divertor surface and exhaust route under the divertor, respectively. On the tile surface, large number of dust was found, in particular, at the inner divertor rather upper area of the deposition layers, where recycling neutrals are increased during discharges. On the other hand, significant amount of dust (20-50 times larger) was generally accumulated at the bottom divertor, in particular, the plasma-unexposed area (remote area). It was found that the poloidal distribution is relatively symmetrical in the toroidal direction within a factor of three. Recently, analysis of dust spatial and size distributions, and evaluation of fuel retention in dust have been progressed. The total amount of the hydrogen isotope contained in the dust was estimated.

Journal Articles

Characteristics of tungsten and carbon dusts in JT-60U and evaluation of hydrogen isotope retention

Ashikawa, Naoko*; Asakura, Nobuyuki; Fukumoto, Masakatsu; Hayashi, Takao; Ueda, Yoshio*; Muroga, Takeo*

Journal of Nuclear Materials, 438, p.S664 - S667, 2013/07

 Times Cited Count:5 Percentile:52.28(Materials Science, Multidisciplinary)

In this study, W concentrations of dusts at P-8 section and hydrogen isotope retentions in dusts are analyzed. Compositions of C including W material dusts were observed in JT-60U. For an enhanced resolution of the XPS measurement to analyze quantitatively the composition of the dust flakes, the new analysis using XPS with indium foil was done and showed that the dust flakes contains about less than 1% of tungsten in carbon. Compositions of tungsten-carbon mixed dusts at different poloidal positions are reported. Produced areas of dust including W is estimated on the outer doom wing by IMPGYRO code. Relative intensities at low temperature regions were smaller than bulk divertor target, which may be caused by the high baking/operation temperature. Amounts of retained Hydrogen/Deuterium in dust particles depend on internal defects and carbon composition of dusts.

Journal Articles

In-vessel tritium

Ueda, Yoshio*; Oya, Kaoru*; Ashikawa, Naoko*; Ito, Atsushi*; Ono, Tadayoshi*; Kato, Daiji*; Kawashima, Hisato; Kawamura, Gakushi*; Kenmotsu, Takahiro*; Saito, Seiki*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 88(9), p.484 - 502, 2012/09

no abstracts in English

Journal Articles

Measurements of carbon dust property in experiment and post-campaign sampling on JT-60U Tokamak

Asakura, Nobuyuki; Hayashi, Takao; Ashikawa, Naoko*; Hatae, Takaki; Nakano, Tomohide

Fusion Science and Technology, 60(4), p.1572 - 1575, 2011/11

 Times Cited Count:5 Percentile:54.65(Nuclear Science & Technology)

Dust research has been performed in JT-60U in order to predict the plasma performance and the tritium retention in a fusion reactor. Laser scattering measurement showed, in specific discharge after disruptions, both the size and number were peaked in the far-SOL and they decreased near the separatrix. This result shows that sublimation of dust is dominant in the SOL. Dust collection after the experiment campaign showed that large weight of the dust was cumulated on the exhaust route of gas flow under the divertor. The total amount of the hydrogen isotope contained in the dust were estimated for the cases with deposited in the volume and near the surface.

Journal Articles

Measurement of dust quantity and distribution collected from JT-60U

Hayashi, Takao; Asakura, Nobuyuki; Ashikawa, Naoko*; Nakano, Tomohide

Fusion Science and Technology, 60(4), p.1548 - 1551, 2011/11

 Times Cited Count:2 Percentile:77.85(Nuclear Science & Technology)

A real mass densities of carbon dust collected in the baffle and divertor regions of JT-60U were investigated. On the plasma-exposed surface, large areal density of 610 mg/m$$^{2}$$ is found at the upper tile of the inner divertor, which is much larger than other areas due to the soft deposition. On the other hand, as for the plasma-shadowed area, largest areal density of 5,100 mg/m$$^{2}$$ was found underneath the dome structure. The total dust weights at the plasma-exposed surface and the shadowed areas were estimated to be 1.3 g and 22.2 g, respectively, assuming the toroidal symmetry. Count-based size distributions were also investigated. The average dust size of the main population is less than 20 $$mu$$m for both the plasma-exposed surface and the shadowed area.

Journal Articles

Report on ITPA meeting, 33

Asakura, Nobuyuki; Ashikawa, Naoko*; Ueda, Yoshio*; Ono, Noriyasu*; Tanabe, Tetsuo*; Nakano, Tomohide; Masuzaki, Suguru*; Itami, Kiyoshi; Kawano, Yasunori; Kawahata, Kazuo*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 87(7), p.485 - 486, 2011/07

no abstracts in English

Journal Articles

28th report on the ITPA (International Tokamak Physics Activity) meeting

Asakura, Nobuyuki; Nakano, Tomohide; Masuzaki, Takashi*; Ashikawa, Naoko*; Ueda, Yoshio*; Tanabe, Tetsuo*; Ono, Noriyasu*

Purazuma, Kaku Yugo Gakkai-Shi, 86(2), P. 124, 2010/02

no abstracts in English

Journal Articles

Tritium science and technology for fusion reactor, 3; Theory and code development for evaluation of tritium retention and exhaust in fusion reactor

Oya, Kaoru*; Inai, Kensuke*; Shimizu, Katsuhiro; Takizuka, Tomonori; Kawashima, Hisato; Hoshino, Kazuo; Hatayama, Akiyoshi*; Toma, Mitsunori*; Tomita, Yukihiro*; Kawamura, Gakushi*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 85(10), p.695 - 703, 2009/10

no abstracts in English

Journal Articles

Report on ITPA meetings, 24

Idomura, Yasuhiro; Yoshida, Maiko; Yagi, Masatoshi*; Tanaka, Kenji*; Hayashi, Nobuhiko; Sakamoto, Yoshiteru; Tamura, Naoki*; Oyama, Naoyuki; Urano, Hajime; Aiba, Nobuyuki; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 84(12), p.952 - 955, 2008/12

no abstracts in English

Journal Articles

Research and development of imaging bolometers

Peterson, B. J.*; Konoshima, Shigeru; Kostryukov, A. Y.*; Seo, D. C.*; Liu, Y.*; Miroshnikov, I. V.*; Ashikawa, Naoko*; Parchamy, H.*; Kawashima, Hisato; Iwama, Naofumi*; et al.

Plasma and Fusion Research (Internet), 2, p.S1018_1 - S1018_4, 2007/11

An overview of the research and development of imaging bolometers giving a perspective on the applicability of this diagnostic to a fusion reactor is presented. Traditionally the total power lost from a high temperature has been measured using one dimensional arrays of resistive bolometers. The large number of signal wires associated with these resistive bolometers poses hazards not only at the vacuum interface, but also in the loss of electrical contacts that has been observed in the presence of fusion reactor levels of neutron flux. Infrared imaging video bolometers (IRVB), on the other hand, use the infrared radiation from the absorbing metal foil to transfer the signal through the vacuum interface and out from behind a neutron shield. The IRVB can provide hundreds of channels of bolometric signal in an image of the plasma radiation. Recently a prototype IRVB has been deployed on the JT-60U tokamak which demonstrates the ability of this diagnostic to operate in a reactor environment.

Journal Articles

Spatial variation of the foil parameters from in situ calibration of the JT-60U imaging bolometer foil

Araghy, H. P.*; Peterson, B. J.*; Hayashi, Hiromi*; Konoshima, Shigeru; Ashikawa, Naoko*; Seo, D. C.*; JT-60U Team

Plasma and Fusion Research (Internet), 2, p.S1116_1 - S1116_4, 2007/11

We obtain the local foil properties of the JT-60U imaging bolometer foil (a single graphite-coated gold foil with an effective area of 9 $$times$$ 7 cm$$^{2}$$ and a nominal thickness of 2.5 microns) such as the thermal diffusivity and the product of the thermal conductivity and the thickness of the foil by the foil calibration. Calibration of the foil was made in situ using a He-Ne laser ($$sim$$27 mW) as a known radiation source to heat the foil. The thermal images of the foil are provided by an IR camera (micro-bolometer type). The parameters are determined by finite element modeling of the foil temperature and comparing the solution to the experimental results. In this work we apply this calibration technique to investigate the spatial variation of the foil parameters. Significant variation in the local temperature rise of the foil due to local heating by the laser beam indicates a spatial variation of the foil parameters. This variation is possibly due to nonuniformity in the carbon coating and/or the thickness of the foil. In a separate work, the spatial calibration data will be used to produce the bolometer intensity data to be utilized in the tomographic analyses.

Journal Articles

Dynamics of deuterium implanted in boron coating film for wall conditioning

Nakahata, Toshihiko*; Yoshikawa, Akira*; Oyaizu, Makoto*; Oya, Yasuhisa*; Ishimoto, Yuki*; Kizu, Kaname; Yagyu, Junichi; Ashikawa, Naoko*; Nishimura, Kiyohiko*; Miya, Naoyuki; et al.

Journal of Nuclear Materials, 367-370(2), p.1170 - 1174, 2007/08

 Times Cited Count:2 Percentile:79.35(Materials Science, Multidisciplinary)

Retention and desorption behavior of deuterium implanted into pure boron films has been studied by means of the secondary ion mass spectroscopy. It was found that the factor dominating deuterium desorption was the sample temperature. At stage 1, below 573 K, the desorption of deuterium from B-D-B bond dominated and diffusion was the rate-determining process in this stage. Above 573 K, deuterium was mainly desorbed from B-D bonds, and recombination was the rate-determining process in this stage. The effective molecular recombination rate constant of deuterium trapped as B-D bond was determined by an isothermal annealing experiment.

Journal Articles

Observation of divertor and core radiation in JT-60U by means of bolometric imaging

Peterson, B. J.*; Konoshima, Shigeru; Parchamy, H.*; Kaneko, Masashi*; Omori, Toshimichi*; Seo, D. C.*; Ashikawa, Naoko*; Sukegawa, Atsuhiko; JT-60 Team

Journal of Nuclear Materials, 363-365, p.412 - 415, 2007/06

 Times Cited Count:11 Percentile:34.46(Materials Science, Multidisciplinary)

Diagnosis of the radiation from both the divertor and core plasma regions is a key issue for the study of impurities resulting from plasma-surface interaction in existing magnetic plasma confinement experiments and future fusion reactors. An infrared imaging video bolometer has been designed, fabricated and installed on the JT-60U tokamak. This diagnostic utilizes an IR camera to image the temperature change of a thin foil which is exposed to plasma radiation through an aperture resulting in an image of the incident plasma radiation absorbed by the foil. In the 2004-2005 experimental campaign intitial data was taken which was limited to 8-bit analog video data from ohmic and hydrogen neutral beam discharges due to inadequate shielding. The semitangential, wide-angle view of the plasma covers the entire poloidal cross-section and the divertor extending over 90 degrees toroidally. This preliminary data showed a strong radiation zone from the divertor that moved up into the core plasma as the discharge terminated in agreement with the data from the resistive bolometer arrays. For the current campaign we have upgraded the system by improving the shielding against neutrons, $$gamma$$ and magnetic field. This has enabled operation of the camera during high magnetic field and some high power deuterium neutral beam discharges. We also improved the triggering and data transmission system to acquire 14-bit digital data. This will allow processing of the IR camera data to produce images of the radiation brightness at the foil which can be viewed as a movie with a frame rate of 30 fps. This data is used to study the toroidal uniformity of the radiation from the divertor in JT-60U.

Journal Articles

Comparison of boronized wall in LHD and JT-60U

Ashikawa, Naoko*; Kizu, Kaname; Yagyu, Junichi; Nakahata, Toshihiko*; Nobuta, Yuji; Nishimura, Kiyohiko*; Yoshikawa, Akira*; Ishimoto, Yuki*; Oya, Yasuhisa*; Okuno, Kenji*; et al.

Journal of Nuclear Materials, 363-365, p.1352 - 1357, 2007/06

 Times Cited Count:9 Percentile:40.6(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

The Effect of argon and helium glow discharge cleaning on boronized surface in LHD

Kizu, Kaname; Yagyu, Junichi; Ishimoto, Yuki*; Nakano, Tomohide; Tsuzuki, Kazuhiro*; Miya, Naoyuki; Ashikawa, Naoko*; Nishimura, Kiyohiko*; Sagara, Akio*

Annual Report of National Institute for Fusion Science; April 2005 - March 2006, P. 65, 2006/11

no abstracts in English

Journal Articles

Detailed ${it in situ}$ laser calibration of the infrared imaging video bolometer for the JT-60U tokamak

Parchamy, H.*; Peterson, B. J.*; Konoshima, Shigeru; Hayashi, Hiromi*; Seo, D. C.*; Ashikawa, Naoko*; JT-60U Team

Review of Scientific Instruments, 77(10), p.10E515_1 - 10E515_4, 2006/10

 Times Cited Count:13 Percentile:41.57(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Radiated power profile observed by a tangentially viewing IR imaging bolometer in JT-60U tokamak

Konoshima, Shigeru; Peterson, B. J.*; Ashikawa, Naoko*; Miura, Yukitoshi; JT-60 Team

Europhysics Conference Abstracts (CD-ROM), 29C, 4 Pages, 2005/00

An IR imaging bolometer with semi-tangential views of the diverted tokamak has been designed and installed in JT-60U in 2003-2004. A 2.5 microns gold absorber foil of 9 cm $$times$$ 7 cm was shown to be durable during two years of operation with 1800 tokamak discharges including disruptions. Some unique analog video data from the IR camera characterizing diverted tokamak discharges have been obtained during test operation. A radiating toroidal ring has been mapped and recorded onto the foil as a clear high temperature zone at the disruption, consistent with huge core radiation measured by the resistive bolometers. Divertor radiation near the W-shaped divertor tiles of JT-60U could be identified also in the foil image as a thick line having toroidal curvature.

Journal Articles

Imaging bolometer for a burning plasma experiment

Peterson, B. J.*; Ashikawa, Naoko*; Konoshima, Shigeru; Ingesson, L. C.*; Walker, C. I.*

Proceedings of 30th EPS Conference on Controlled Fusion and Plasma Physics (CD-ROM), 4 Pages, 2003/00

Research and development of imaging bolometers has progressed from the Segmented Mask IR Imaging Bolometer to the IR Imaging Video Bolometer (IRVB). Meanwhile tests of conventional resistive bolometers have shown their weakness to the high neutron flux. In this paper we compare the IRVBs currently installed in the Large Helical Device with a conceptual design for the JT-60U tokamak and a feasibility study for the International Thermonuclear Experimental Reactor. Comparisons are made with conventional resistive bolometers in terms of sensitivity, spatial and time resolution, port access requirements, steady-state operation, long term durability and shielding of stray ECH power.

Oral presentation

Imaging bolometer development for application to fusion reactor diagnostics

Peterson, B. J.*; Alekseyev, A. G.*; Konoshima, Shigeru; Ashikawa, Naoko*; Parchamy, H.*; Sasao, Mamiko*; Miura, Yukitoshi

no journal, , 

The imaging bolometer concept is based on a thin foil which absorbs the broad-band radiation and/or energetic particles from the plasma. The resulting temperature change in the foil is measured by an infrared camera located outside the vacuum vessel. Development of imaging bolometers is being carried out for application in bolometry and lost alpha diagnosis for fusion reactors. In the case of an imaging bolometer, placing the foil behind a pinhole camera provides a two-dimensional image of the plasma radiation. In the case of a lost alpha diagnostic the foil is placed behind multiple layers of thin foils with one dimension being used for energy discrimination and the other layer being used for pitch angle discrimination. The work described includes the operation of imaging bolometers on the Large Helical Device and the JT-60U Tokamak, calibration experiments, testing prototype lost alpha diagnostic detectors on an ion beam facility and the design of an imaging bolometer and a lost alpha diagnostic for ITER.

35 (Records 1-20 displayed on this page)