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Journal Articles

Updating legacy CAMAC-based data acquisition system for extended pulse duration of JT-60U

Sato, Minoru; Kiyono, Kimihiro; Oshima, Takayuki; Sakata, Shinya; Konoshima, Shigeru; Ozeki, Takahisa

Fusion Engineering and Design, 83(2-3), p.334 - 336, 2008/04

 Times Cited Count:2 Percentile:18.72(Nuclear Science & Technology)

JT-60U's diagnostic systems have been using CAMAC systems for their control and data acquisition. But the transient recorders used to store the diagnostic data are rather old and lack in memory expansion. Therefore, for a long pulse discharge of more than 15 seconds, data sampling rate must be reduced to cover the whole discharge period. The acquired data has, however, low time resolution and is sometimes insufficient for detailed analysis. To solve this problem, the transient recorders should be replaced with those having larger memory, but without modification to the existing data processing infrastructure. For this purpose, we have developed a new data acquisition system with SPARC CPU on VMEbus and the associated software, to retain the functionality of CAMAC control. We have applied this system to the existing bolometric diagnostics. In this paper, detail of design will be described.

Journal Articles

Volume recombination of C$$^{4+}$$ in detached divertor plasmas of JT-60U

Nakano, Tomohide; Kubo, Hirotaka; Asakura, Nobuyuki; Shimizu, Katsuhiro; Konoshima, Shigeru; Fujimoto, Kayoko; Kawashima, Hisato; Higashijima, Satoru

Nuclear Fusion, 47(11), p.1458 - 1467, 2007/11

 Times Cited Count:20 Percentile:60.65(Physics, Fluids & Plasmas)

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

Application of tomographic imaging to multi-pixel bolometric measurements

Liu, Y.*; Tamura, Naoki*; Peterson, B. J.*; Iwama, Naofumi*; Konoshima, Shigeru; LHD Experimental Group*; JT-60 Team

Plasma and Fusion Research (Internet), 2, p.S1124_1 - S1124_4, 2007/11

Two improved tomographic algorithms, including a linear (Tikhonov-Phillips) and a nonlinear (maximum entropy) regularisation method, have been employed for multi-pixel bolometric measurements in order to get as much information as possible while keeping the assumptions to a minimum. The most important features of these improved methods are the capability of reconstructing radiation distributions without any symmetry assumptions, built-in smoothing, and useful reconstructions with relatively few detectors. Furthermore, the effects of finite detector size have been taken into account with a full three dimensional treatment of the detector geometry. The application of tomographic imaging was implemented to a two-array X-ray camera on the Large Helical Device (LHD) and a two-dimensional infrared imaging bolometric pinhole camera on JT-60U. Pertinent examples of the results are presented both to illustrate the analysis techniques and to demonstrate the wealth of physics which can be studied.

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

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:12 Percentile:66.47(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

Progress in the ITER physics basis, 4; Power and particle control

Loarte, A.*; Lipschultz, B.*; Kukushkin, A. S.*; Matthews, G. F.*; Stangeby, P. C.*; Asakura, Nobuyuki; Counsell, G. F.*; Federici, G.*; Kallenbach, A.*; Krieger, K.*; et al.

Nuclear Fusion, 47(6), p.S203 - S263, 2007/06

 Times Cited Count:726 Percentile:96.49(Physics, Fluids & Plasmas)

Progress, since the ITER Physics Basis publication (1999), in understanding the processes that will determine the properties of the plasma edge and its interaction with material elements in ITER is described. Significant progress in experiment area: energy and particle transport, the interaction of plasmas with the main chamber material elements, ELM energy deposition on material elements and the transport mechanism, the physics of plasma detachment and neutral dynamics, the erosion of low and high Z materials, their transport to the core plasma and their migration at the plasma edge, retention of tritium in fusion devices and removal methods. This progress has been accompanied by the development of modelling tools for the physical processes at the edge plasma and plasma-materials interaction. The implications for the expected performance in ITER and the lifetime of the plasma facing materials are discussed.

Journal Articles

Radiation processes of impurities and hydrogen in detached divertor plasmas of JT-60U

Nakano, Tomohide; Kubo, Hirotaka; Asakura, Nobuyuki; Shimizu, Katsuhiro; Konoshima, Shigeru; Fujimoto, Kayoko; Kawashima, Hisato; Higashijima, Satoru

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

Volume recombination of C$$^{4+}$$ and $$e^{-}$$ into C$$^{3+}$$ is observed for the first time in detached plasmas with MARFE. It is found that the recombination flux of C$$^{4+}$$ to C$$^{3+}$$ is comparable to the ionization flux of C$$^{3+}$$ to C$$^{4+}$$, and that the recombination zone is above an X-point and beneath the ionization zone. This result suggests that this volume recombination predominantly produces C$$^{3+}$$ ions, which contribute 60-80 % to the total radiation power in the divertor plasma.

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:57.01(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Impact of wall saturation on particle control in long and high-power-heated discharges in JT-60U

Nakano, Tomohide; Asakura, Nobuyuki; Takenaga, Hidenobu; Kubo, Hirotaka; Miura, Yukitoshi; Shimizu, Katsuhiro; Konoshima, Shigeru; Masaki, Kei; Higashijima, Satoru; JT-60 Team

Nuclear Fusion, 46(5), p.626 - 634, 2006/05

 Times Cited Count:19 Percentile:56.94(Physics, Fluids & Plasmas)

In order to understand plasma-wall interactions in a long time scale, the discharge pulse length has been extended from 15 s to 65 s, with the NB-heating duration extended to 30 s. Nearly-saturation of the divertor plates was observed in the latter half of long pulse ELMy H-mode discharges. Particle sink into the divertor plates gradually decreased, and subsequently, wall-pumping efficiency became zero. This wall saturation resulted in a rise of the main plasma density without any auxiliary particle supply besides NB with divertor-pumping. Even when the total injected energy reached up to $$sim$$ 350 MJ in a discharge, neither sudden increase of carbon generation such as carbon bloom nor increase of the dilution of the main plasma was observed.

Journal Articles

Study of global wall saturation mechanisms in long-pulse ELMy H-mode discharges on JT-60U

Takenaga, Hidenobu; Nakano, Tomohide; Asakura, Nobuyuki; Kubo, Hirotaka; Konoshima, Shigeru; Shimizu, Katsuhiro; Tsuzuki, Kazuhiro; Masaki, Kei; Tanabe, Tetsuo*; Ide, Shunsuke; et al.

Nuclear Fusion, 46(3), p.S39 - S48, 2006/03

 Times Cited Count:18 Percentile:54.9(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Modeling of impurity transport in high density plasma with highly enhanced radiation loss on JT-60U

Takenaga, Hidenobu; Asakura, Nobuyuki; Kubo, Hirotaka; Konoshima, Shigeru; Nakano, Tomohide; Porter, G.*; Rognlien, T.*; Rensink, M.*

Journal of Plasma and Fusion Research SERIES, Vol.7, p.35 - 39, 2006/00

no abstracts in English

Journal Articles

Compatibility of advanced tokamak plasma with high density and high radiation loss operation in JT-60U

Takenaga, Hidenobu; Asakura, Nobuyuki; Kubo, Hirotaka; Higashijima, Satoru; Konoshima, Shigeru; Nakano, Tomohide; Oyama, Naoyuki; Porter, G. D.*; Rognlien, T. D.*; Rensink, M. E.*; et al.

Nuclear Fusion, 45(12), p.1618 - 1627, 2005/12

 Times Cited Count:18 Percentile:53.86(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Study of plasma wall interactions in the long-pulse NB-heated discharges of JT-60U towards steady-state operation

Takenaga, Hidenobu; Asakura, Nobuyuki; Higashijima, Satoru; Nakano, Tomohide; Kubo, Hirotaka; Konoshima, Shigeru; Oyama, Naoyuki; Isayama, Akihiko; Ide, Shunsuke; Fujita, Takaaki; et al.

Journal of Nuclear Materials, 337-339, p.802 - 807, 2005/03

 Times Cited Count:14 Percentile:70.37(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Effects of long time scale variation of plasma wall interactions on particle control in JT-60U

Takenaga, Hidenobu; Nakano, Tomohide; Asakura, Nobuyuki; Kubo, Hirotaka; Konoshima, Shigeru; Shimizu, Katsuhiro; Tsuzuki, Kazuhiro; Ide, Shunsuke; Fujita, Takaaki

Proceedings of 4th IAEA Technical Meeting on Steady-State Operation of Magnetic Fusion Devices and MHD of Advanced Scenarios (Internet), 8 Pages, 2005/02

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

Characteristics of runaway plasmas in JT-60U

Kawano, Yasunori; Nakano, Tomohide; Isayama, Akihiko; Hatae, Takaki; Konoshima, Shigeru; Oyama, Naoyuki; Kondoh, Takashi; Tamai, Hiroshi; Kubo, Hirotaka; Asakura, Nobuyuki; et al.

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

In order to mitigate the post-disruption runaway electrons, experiments has been carried out with impurity pellet injection. As a result, we have observed the prompt exhaust of the runaway electrons and the reduction of runaway plasma. We have presented one possible explanation for basic behavior of the runaway plasma current that it follows the balance of the avalanche generation of runaway electrons and their slowing down predicted by the model, including effects by synchrotron radiation. On the other hand, standing on the fact that the current quench time is extended by runaway electrons, the experiment for avoiding the current quench by runaway electrons has been carried out. The runaway electrons reinforced the discharge to survive against the low Te of less than several tens eV and an additional impurity pellet injection, and thus the plasma current was maintained and terminated as programmed. To study the dynamics of runaway electrons precisely, a new active and direct diagnostic concept using the laser inverse Compton scattering has been proposed.

Journal Articles

Compatibility of advanced tokamak plasma with high density and high radiation loss operation in JT-60U

Takenaga, Hidenobu; Asakura, Nobuyuki; Kubo, Hirotaka; Higashijima, Satoru; Konoshima, Shigeru; Nakano, Tomohide; Oyama, Naoyuki; Porter, G. D.*; Rognlien, T. D.*; Rensink, M. E.*; et al.

Proceedings of 20th IAEA Fusion Energy Conference (FEC 2004) (CD-ROM), 8 Pages, 2004/11

no abstracts in English

Journal Articles

Two-dimensional distribution of divertor radiation in JT-60U

Konoshima, Shigeru; Tamai, Hiroshi; Miura, Yukitoshi; Higashijima, Satoru; Kubo, Hirotaka; Sakurai, Shinji; Shimizu, Katsuhiro; Takizuka, Tomonori; Koide, Yoshihiko; Hatae, Takaki; et al.

Journal of Nuclear Materials, 313-316(1-3), p.888 - 892, 2003/03

 Times Cited Count:18 Percentile:76.42(Materials Science, Multidisciplinary)

The emissivity distribution of the JT-60U divertor plasmas has been studied with the bolometer diagnostics. Line integrated bolometer signals of 48 chords have been successfully mapped onto the JT-60U W-shaped divertor geometry. 2D radiation profiles provide an intuitive understanding of the experiments and comparison of experiment with simulation for divertor characterization. An extended region of the radiation along both divertor legs was found in ELMing H-mode discharges with line-average density of 3.7x10$$^{19}$$m$$^{-3}$$. A highly radiative zone with an emissivity of around 15 MWm$$^{-3}$$ at the inboard side and around 8 MWm$$^{-3}$$ at outboard side has been identified to extend more than 10 cm from each target plate toward the x-point. About 70 % of the input neutral beam power, 11 MW, is dissipated as a divertor radiation in that region.

Journal Articles

Radiation enhancement and impurity behavior in JT-60U reversed shear discharges

Kubo, Hirotaka; Sakurai, Shinji; Higashijima, Satoru; Takenaga, Hidenobu; Itami, Kiyoshi; Konoshima, Shigeru; Nakano, Tomohide; Koide, Yoshihiko; Asakura, Nobuyuki; Shimizu, Katsuhiro; et al.

Journal of Nuclear Materials, 313-316(1-3), p.1197 - 1201, 2003/03

 Times Cited Count:18 Percentile:76.42(Materials Science, Multidisciplinary)

no abstracts in English

62 (Records 1-20 displayed on this page)