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Journal Articles

Dynamics of ion internal transport barrier in LHD heliotron and JT-60U tokamak plasmas

Ida, Katsumi*; Sakamoto, Yoshiteru; Yoshinuma, Mikiro*; Takenaga, Hidenobu; Nagaoka, Kenichi*; Hayashi, Nobuhiko; Oyama, Naoyuki; Osakabe, Masaki*; Yokoyama, Masayuki*; Funaba, Hisamichi*; et al.

Nuclear Fusion, 49(9), p.095024_1 - 095024_9, 2009/09

 Times Cited Count:26 Percentile:26.42(Physics, Fluids & Plasmas)

Dynamics of ion internal transport barrier (ITB) formation and impurity transport both in the Large Helical Device (LHD) heliotron and JT-60U tokamak are described. Significant differences between heliotron and tokamak plasmas are observed. The location of the ITB moves outward during the ITB formation regardless of the sign of magnetic shear in JT-60U and the ITB becomes more localized in the plasma with negative magnetic shear. In LHD, the low Te/Ti ratio ($$<$$ 1) of the target plasma for the high power heating is found to be necessary condition to achieve the ITB plasma and the ITB location tends to expand outward or inward depending on the condition of the target plasmas. Associated with the formation of ITB, the carbon density tends to be peaked due to inward convection in JT-60U, while the carbon density becomes hollow due to outward convection in LHD. The outward convection observed in LHD contradicts the prediction by neoclassical theory.

Journal Articles

Spectroscopic observations of beam and source plasma light and testing Cs-deposition monitor in the large area negative ion source for LHD-NBI

Oka, Yoshihide*; Tsumori, Katsuyoshi*; Ikeda, Katsunori*; Kaneko, Osamu*; Nagaoka, Kenichi*; Osakabe, Masaki*; Takeiri, Yasuhiko*; Asano, Eiji*; Komada, Seiji*; Kondo, Tomoki*; et al.

Review of Scientific Instruments, 79(2), p.02C105_1 - 02C105_4, 2008/02

 Times Cited Count:0 Percentile:100(Instruments & Instrumentation)

In the present studies, we studied the cesium lines in the source plasma during beam shots on the LND MN-NBI system. It was found for the first time in the LHD-source 2, that both the amount of Cs I (neutral Cs) and Cs II (Cs$$^{+}$$) in the source plasma light rose sharply when beam acceleration began, and continued rising during a 10 s pulse. We think that this was because the cesium was evaporated/sputtered from the source backplate by the back-streaming positive ions.

Journal Articles

Depositional records of plutonium and $$^{137}$$Cs released from Nagasaki atomic bomb in sediment of Nishiyama reservoir at Nagasaki

Kokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Yamazaki, Hideo*; Yoshikawa, Shusaku*; Nagaoka, Shinji*; Mitamura, Muneki*; et al.

Journal of Environmental Radioactivity, 99(1), p.211 - 217, 2008/01

 Times Cited Count:15 Percentile:61.68(Environmental Sciences)

In a sediment core of Nishiyama reservoir at Nagasaki, depth profiles of $$^{240}$$Pu/$$^{239}$$Pu ratio, $$^{239+240}$$Pu and $$^{137}$$Cs concentrations were determined. Sediments containing plutonium and $$^{137}$$Cs, which were fallout deposited immediately after a detonation of Nagasaki atomic bomb, were identified in the core. Observed below the sediments were macroscopic charcoals, providing evidence for initial deposit of the fallout. This is the first entire depositional records of plutonium and $$^{137}$$Cs released from the Nagasaki atomic bomb together with those from atmospheric nuclear tests.

Journal Articles

Escaping ion measurement with high time resolution during bursting modes induced by neutral beam injection on CHS

Shinohara, Koji; Isobe, Mitsutaka*; Darrow, D. S.*; Shimizu, Akihiro*; Nagaoka, Kenichi*; Okamura, Shoichi*

Plasma and Fusion Research (Internet), 2, p.042_1 - 042_8, 2007/09

Journal Articles

Studies of fast-ion transport induced by energetic particle modes using fast-particle diagnostics with high time resolution in CHS

Isobe, Mitsutaka*; Toi, Kazuo*; Matsushita, Hiroyuki*; Goto, Kazuyuki*; Suzuki, Chihiro*; Nagaoka, Kenichi*; Nakajima, Noriyoshi*; Yamamoto, Satoshi*; Murakami, Sadayoshi*; Shimizu, Akihiro*; et al.

Nuclear Fusion, 46(10), p.S918 - S925, 2006/10

 Times Cited Count:25 Percentile:32.42(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Experimental study of nonlinear processes in edge turbulence of toroidal plasmas

Nagashima, Yoshihiko*; Hoshino, Katsumichi; Nagaoka, Kenichi*; Shinohara, Koji; Fujisawa, Akihide*; Uehara, Kazuya; Kusama, Yoshinori; Ida, Katsumi*; Yoshimura, Yasuo*; Okamura, Shoichi*; et al.

Plasma and Fusion Research (Internet), 1(9), p.041_1 - 041_15, 2006/09

Nonlinear processes between meso-scale structures and turbulent fluctuations in the edge region of the toroidal plasmas were studied using the bispectrum analysis. In the JFT-2M tokamak, divertor plasmas were investigated as well as the limiter plasmas, and the amplitude and phase of the bispectrum function of the potential fluctuation were found to be consistent with an analysis of the drift wave-zonal flow system. In the CHS machine, the edge plasmas during the H-mode were investigated. It was found that the edge potential begins to decrease before the decrease of the intensity of the deuterium line (by about 30ms), and the edge fluctuations are found to be composed of low frequency MHD fluctuations, drift wave like broad band electrostatic fluctuations and high frequency electromagnetic fluctuations. Nonlinear coupling between the MHD fluctuations and the electrostatic fluctuations or the electromagnetic fluctuations were found for the first time.

Journal Articles

Energetic ion measurements using a directional probe

Nagaoka, Kenichi*; Isobe, Mitsutaka*; Shinohara, Koji; Osakabe, Masaki*; Shimizu, Akihiro*; Okamura, Shoichi*

Plasma and Fusion Research (Internet), 1(1), p.005_1 - 005_2, 2006/01

A directional Langmuir probe (DLP) method has been applied for energetic particles (ions) measurement in a magnetically confined plasma. Two experimental demonstrations have been performed in the compact helical system (CHS). One is neutral beam modulation experiment and the other is the measurement of energetic ion loss induced by MHD bursts. The results of the DLP are consistent with that of a neutral particle analyzer (NPA) and a lost ion probe (LIP). These experiments show that this method is applicable outside and also inside of the last closed flux surface.

Journal Articles

Observation of nonlinear processes between coherent fluctuations and turbulent fluctuations in the edge regions of JFT-2M and CHS

Nagashima, Yoshihiko*; Ito, Kimitaka*; Ito, Sanae*; Fujisawa, Akihide*; Hoshino, Katsumichi; Nagaoka, Kenichi*; Ejiri, Akira*; Takase, Yuichi*; Yagi, Masatoshi*; Shinohara, Koji; et al.

Europhysics Conference Abstracts (CD-ROM), 30I, 4 Pages, 2006/00

The results of the analyses of nonlinear processes in the plasma in JFT-2M tokamak and CHS machine are reported. In both machines, the measurements of the fluctuations were done by electrostatic probes. The obtained bicoherence and biphase from the potential data in JFT-2M were found to be close to the values obtained from a theoretical model of the interaction of the zonal flow and the drift wave turbulence. Therefore the experimentally obtained nonlinear interaction is considered to be that interaction of the zonal flow and the drift wave turbulence. By the analysis of the CHS H-mode plasma, a marked nonlinear interaction was found between a characteristic MHD magnetic fluctuation and density turbulence. By analysing the cross bispectrum of the density fluctuation and the potential fluctuation, it was found that the fluctuating particle flux is affected by the MHD oscillation. As stated above, we progressed in the investigation of the nonlinear processes of the edge plasmas.

Journal Articles

Heating and current drive by N-NBI in JT-60U and LHD

Kaneko, Osamu*; Yamamoto, Takumi; Akiba, Masato; Hanada, Masaya; Ikeda, Katsunori*; Inoue, Takashi; Nagaoka, Kenichi*; Oka, Yoshihide*; Osakabe, Masaki*; Takeiri, Yasuhiko*; et al.

Fusion Science and Technology, 44(2), p.503 - 507, 2003/09

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

High energy negative-ion-based neutral beam injection (N-NBI) is expected as an efficient and reliable tool of heating and current driving for reactor plasmas such as ITER. A world wide activity on developing technology of negative ion production and beam formation started in 1980ユs and the great progress has been achieved up to now. In particular, Japan has two large projects that planned adopting N-NBI for real plasma experiments; the JT-60U tokamak and the LHD heliotron, which further motivated the R&D activity. These R&D programs were carried out at JAERI and NIFS separately in Japan, and both were successfully done. The first beam injection experiment was made on the JT-60U in 1996, followed by the LHD in 1998. They were the first experiments on heating plasma by high energy beam in tokamaks and in stellerators, and the obtained results were very promising.

Oral presentation

Experimental study of nonlinear processes in edge turbulence of toroidal plasmas

Nagashima, Yoshihiko*; Hoshino, Katsumichi; Shinohara, Koji; Uehara, Kazuya; Kusama, Yoshinori; Nagaoka, Kenichi*; Fujisawa, Akihide*; Ida, Katsumi*; Yoshimura, Yasuo*; Okamura, Shoichi*; et al.

no journal, , 

We present an invited talk on the experimental study of the nonlinear interaction processes of the edge plasma turbulence studied in the JFT-2M tokamak machine of JAEA and in the CHS helical machine of the NIFS. We made a progress in understanding the nonlinear interaction of the drift wave turbulence and the zonal flow by measuring the potential fluctuations and density fluctuations by the measurement of the electrostatic probes. We found that the measured indices such as the bicoherence or the biphase are consistent with the results of a theoretical study of the drift-wave-zonal-flow system for the first time. We also made the convergence characteristic of these indices clear against the realization numbers for the first time. The study progresses the understanding of the plasma turbulence and structural formation in the plasma, and the results contributes much to the understanding of the transport process in the plasma.

Oral presentation

Trace of "Black rain" originated from the Nagasaki atomic bomb in sediment of the Nishiyama reservoir at Nagasaki City

Kokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Murakami, Akiko*; Inoue, Jun*; Yoshikawa, Shusaku*; Yamazaki, Hideo*; et al.

no journal, , 

no abstracts in English

Oral presentation

Origin of plutonium in sediments of the Nishiyama reservoir at Nagasaki city

Kokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Yoshikawa, Shusaku*; Yamazaki, Hideo*; Nagaoka, Shinji*

no journal, , 

no abstracts in English

Oral presentation

Plutonium in the Nishiyama area of Nagasaki city

Kokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Yoshikawa, Shusaku*; Yamazaki, Hideo*; Nagaoka, Shinji*

no journal, , 

no abstracts in English

Oral presentation

Escaping ion measurement with high speed camera on CHS

Shinohara, Koji; Isobe, Mitsutaka*; Darrow, D. S.*; Shimizu, Akihiro*; Nagaoka, Kenichi*; Okamura, Shoichi*

no journal, , 

no abstracts in English

Oral presentation

Plutonium and $$^{137}$$Cs derived from Nagasaki atomic bomb; The Sedimentation in Nishiyama reservoir for the last 60 years and the distribution in surface soil at present

Kokubu, Yoko; Yasuda, Kenichiro; Magara, Masaaki; Miyamoto, Yutaka; Sakurai, Satoshi; Usuda, Shigekazu; Yamazaki, Hideo*; Yoshikawa, Shusaku*; Nagaoka, Shinji*

no journal, , 

In order to determine sedimentation of plutonium and $$^{137}$$Cs derived from Nagasaki atomic bomb for the last 60 years, we measured $$^{240}$$Pu/$$^{239}$$Pu ratio and Pu and $$^{137}$$Cs concentration in a sediment core collected at Nishiyama reservoir in Nagasaki city. A layer where plutonium and $$^{137}$$Cs deposited immediately after the detonation was specified in the core. Even at present, the plutonium and $$^{137}$$Cs from the atomic bomb are continuously being deposited together with those of the atmospheric nuclear tests. We also measured the ratios in soils collected at eastern part of Nagasaki prefecture and Kumamoto prefecture and so on to determine the detailed distributions of the plutonium. The ratios in soils collected in the Shimabara peninsula, Kumamoto city and Aso city were relatively lower than value of global fallout from atmospheric nuclear tests. It indicates that the atomic bomb plutonium was deposited between 2 km and about 100 km east from the hypocenter.

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