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Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku*; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*
Scientific Reports (Internet), 7(1), p.14971_1 - 14971_8, 2017/11
Times Cited Count:23 Percentile:77.76(Multidisciplinary Sciences)Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*; et al.
Scientific Reports (Internet), 6, p.30720_1 - 30720_7, 2016/08
Times Cited Count:14 Percentile:64.85(Multidisciplinary Sciences)In this Letter, we report model verifications for a key physics for the L-H transition. Radial electric field excitation, using discharges having a two-step transition. Examining time derivative of Poissons equation, it is found that the sum of the loss cone loss current and neoclassical bulk viscosity current agrees the experimentally observed current in the order of magnitude at the first transition. Following second transition and an ambipolar condition in the L-mode cannot be explained by the models.
Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*; et al.
Nuclear Fusion, 54(7), p.073017_1 - 073017_14, 2014/07
Times Cited Count:28 Percentile:76.90(Physics, Fluids & Plasmas)In the JFT-2M tokamak, limit-cycle oscillation among several variables is observed before L-to-H transition. Spatiotemporal dynamics of the LCO is analyzed in detail. Zonal fows are not seen, and modulation in edge-localized poloidal flow and density gradient is observed. Modulation is also seen in Reynolds stress, caused by that in turbulence intensity and turbulence wavenumber. However, flow acceleration is not able to be explained by the modulation in the Reynolds stress. Rapid inward propagation in density gradient and turbulence packet is also observed. Characteristics of the propagation are veried by means of turbulence spreading theory and diffusion theory.
Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*; et al.
Physical Review Letters, 111(3), p.035002_1 - 035002_5, 2013/07
Times Cited Count:96 Percentile:94.08(Physics, Multidisciplinary)In this Letter, we report analyses of spatiotemporal dynamics of turbulence and structure in the limit cycle oscillation that precedes L-to-H transition. Zonal flows are not observed during LCO, and the oscillation is the periodic generations/decays of barrier with edge localized mean flow. Oscillatory Reynolds stress is found too small to accelerate the LCO flow. Changes of the density gradient and turbulence amplitude are found to propagate into the core in a ballistic manner, suggesting a cause of fast change of core transport after H-mode transition.
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:31.74(Nuclear Science & Technology)Fujisawa, Akihide*; Ido, Takeshi*; Shimizu, Akihiro*; Okamura, Shoichi*; Matsuoka, Keisuke*; Iguchi, Harukazu*; Hamada, Yasuji*; Nakano, Haruhisa*; Oshima, Shinsuke*; Ito, Kimitaka*; et al.
Nuclear Fusion, 47(10), p.S718 - S726, 2007/10
Times Cited Count:103 Percentile:95.12(Physics, Fluids & Plasmas)Present status of experiments on zonal flows is overviewed. Innovative use of modern diagnostics has revealed the existence of zonal flows, their spatio-temporal characteristics, their relationship with turbulence, and their effects on confinement. Particularly a number of observations have been accumulated on the oscillatory branch of the zonal flow, dubbed as geodesic acoustic modes suggesting necessity of theories to give their proper description. Several new methods have elucidated the zonal flow generation processes from the turbulence. Further investigation of relationship between the zonal flows and confinement is strongly encouraged as cross-device activity.
Nagashima, Yoshihiko*; Ito, Kimitaka*; Ito, Sanae*; Fujisawa, Akihide*; Yagi, Masatoshi*; Hoshino, Katsumichi; Shinohara, Koji; Ejiri, Akira*; Takase, Yuichi*; Ido, Takeshi*; et al.
Plasma Physics and Controlled Fusion, 49(10), p.1611 - 1625, 2007/10
Times Cited Count:45 Percentile:80.75(Physics, Fluids & Plasmas)It was found that the envelope of the ambient density fluctuation of the drift wave turbulence has spectral peaks aroound zonal flow frequencies. A method to detect the zonal flow using this characteristic was considered using the JFT-2M density fluctuation data. There is a possibility that the zonal flow will be able to be detected in the future burning plasmas by using the density fluctuations measured by some density fluctuation measurement by such as the microwave reflectometer and so on.
Fujisawa, Akihide*; Ido, Takeshi*; Shimizu, Akihiro*; Okamura, Shoichi*; Matsuoka, Keisuke*; Hamada, Yasuji*; Hoshino, Katsumichi; Nagashima, Yoshihiko*; Shinohara, Koji; Nakano, Haruhisa*; et al.
Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 12 Pages, 2007/03
Present status of experiments on zonal flows is overviewed. Innovative use of traditional and modern diagnostics has revealed unambiguously the existense of the zonal flows, their spatio-temporal caracteristics, their relationship with turbulence, and their effects on confinement. Particularly, a number of observations have been accumulated on the oscillatory branch of zonal flows, dubbed geodesic acoustic modes, suggesting necessity of theories to give their proper description. Furthur investigation of relationship between zonal flows and confinement is strongly encouraged as cross-device activity.
Nagashima, Yoshihiko*; Ito, Kimitaka*; Fujisawa, Akihide*; Ito, Sanae*; Yagi, Masatoshi*; Hoshino, Katsumichi; Shinohara, Koji; Ido, Takeshi*; Miura, Yukitoshi; Ejiri, Akira*; et al.
Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00
The recent results on the identification of the outer most magnetic surface and on the identification of the characteristic of the zonal flow are presented by using the measured data of the zonal flow which is a plasma flow in the tokamak plasma. The positon of the outermost magnetic surface was identified using the characteristic of the oscillating zonal flow called as the geodesic acoutic mode (GAM) that the mode exists only in the closed magnetic surface, and the position of the surface was in agreement with that by the magnetic equilibrium reconstruction. Some coincidence with the drift wave - zonal flow theory was obtained by using the finding that the envelope of the density fluctuation of the background turbulence is modulated by the GAM.
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.
Nagashima, Yoshihiko*; Ito, Kimitaka*; Ito, Sanae*; Hoshino, Katsumichi; Fujisawa, Akihide*; Ejiri, Akira*; Takase, Yuichi*; Yagi, Masatoshi*; Shinohara, Koji; Uehara, Kazuya; et al.
Plasma Physics and Controlled Fusion, 48(5A), p.A377 - A386, 2006/05
Times Cited Count:25 Percentile:62.42(Physics, Fluids & Plasmas)A bispector analysis and envelope moduration analysis of the potential oscillations of a low frequency (1kHz) oscillation, a high frequency (10-15kHz) oscillation and background turbulence are presented. The low frequency mode and the high frequency mode are considered to be a low frequency zonal flow and a geodesic acoustic mode respectively. We could found that the low frequency oscillation has a three wave interaction with the background turbulence as well as the high frequency oscillation does from the bicoherence (nonlinear coupling coefficient), biphase and envelope moduration relation. Apparently, the modulation of the high frequency mode by the low frequency mode was suggested, but it was found that the bicoherence between them is small and the modulation relation was not concluded. Therefore, it is concluded that the nonlinear interaction between the zonal flow - zonal flow system does not exist or the interaction of them is linear if any. Thus it was found that the marked nonlinear interaction occurs only in the turbulence - zonal flow system and not in the zonal flow - zonal flow system.
Ido, Takeshi*; Miura, Yukitoshi; Kamiya, Kensaku; Hamada, Yasuji*; Hoshino, Katsumichi; Fujisawa, Akihide*; Ito, Kimitaka*; Ito, Sanae*; Nishizawa, Akimitsu*; Ogawa, Hiroaki; et al.
Plasma Physics and Controlled Fusion, 48(4), p.S41 - S50, 2006/04
Times Cited Count:129 Percentile:96.47(Physics, Fluids & Plasmas)The potential and density fluctuations of Geodesic-Acoustic-Mode (GAM) were investigated through the direct and simultaneous measurement of electrostatic and density fluctuations with a heavy ion beam probe(HIBP). It was found that the amplitude of the fluctuation has a maximum inside of the plasma boundary and that it has an almost constant frequency. It was also found that the mode propagates in the radial direction and that the GAM affects the background turbulence. The influence to the background turbulence was found to be in consistent with a theoretical prediction.
Nagashima, Yoshihiko*; Ito, Kimitaka*; Ito, Sanae*; Fujisawa, Akihide*; Hoshino, Katsumichi; Takase, Yuichi*; Yagi, Masatoshi*; Ejiri, Akira*; Ida, Katsumi*; Shinohara, Koji; et al.
Plasma Physics and Controlled Fusion, 48(4), p.S1 - S15, 2006/04
Times Cited Count:36 Percentile:74.84(Physics, Fluids & Plasmas)This paper presents the results of bispectral analysis of floating potential fluctuations in the edge region of ohmically heated plasmas in the JFT-2M tokamak. Inside of the outermost magnetic surface,coherent modes were observed around the frequency of geodesic acoustic mode which is a kind of the zonal flow. The squared bicoherence shows significant nonlinear couplings between the coherent fluctuations and the background fluctuations (which are likely to contain drift wave turbulent fluctuations). The experimental results that the total bicoherence is proportional to the squared amplitude of the coherent fluctuation, and that the biphase of the coherent modes localizes around a constant value , are consistent with the theoretical prediction on the drift wave - zonal flow systems based on the Hasegawa-Mima model.
Nagashima, Yoshihiko*; Ito, Sanae*; Yagi, Masatoshi*; Ito, Kimitaka*; Fujisawa, Akihide*; Hoshino, Katsumichi; Shinohara, Koji; Uehara, Kazuya; Kusama, Yoshinori; Ejiri, Akira*; et al.
Review of Scientific Instruments, 77(4), p.045110_1 - 045110_6, 2006/04
Times Cited Count:12 Percentile:51.71(Instruments & Instrumentation)A convergence study of bispector non-linear analysis applied to the fluctuation of toroidal plasmas is studied. A theoretical study of the convergence is presented. And it was found that the convergence property of the total bicoherence and bispector of the fluctuations of drift wave or zonal flow observed in the JFT-2M tokamak plasma is consistent with the theoretical analysis, and also found that the realization number for the convergence is fairly large, for example about 1000 for the JFT-2M experimental fluctuation data. As stated, we made a base for such fluctuation analysis.
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.
Ida, Katsumi*; Fujita, Takaaki; Fukuda, Takeshi*; Sakamoto, Yoshiteru; Ide, Shunsuke; Toi, Kazuo*; Inagaki, Shigeru*; Shimozuma, Takashi*; Kubo, Shin*; Idei, Hiroshi*; et al.
Plasma Physics and Controlled Fusion, 46(5A), p.A45 - A50, 2004/05
Times Cited Count:19 Percentile:52.43(Physics, Fluids & Plasmas)no abstracts in English
Fujita, Takaaki; Fukuda, Takeshi*; Sakamoto, Yoshiteru; Ide, Shunsuke; Suzuki, Takahiro; Takenaga, Hidenobu; Ida, Katsumi*; Idei, Hiroshi*; Shimozuma, Takashi*; Fujisawa, Akihide*; et al.
Plasma Physics and Controlled Fusion, 46(5A), p.A35 - A43, 2004/05
Times Cited Count:26 Percentile:63.12(Physics, Fluids & Plasmas)no abstracts in English
Ida, Katsumi*; Okano, Kunihiko*; Ogawa, Yuichi*; Kamada, Yutaka; Kimura, Haruyuki; Nishihara, Katsunobu*; Fujisawa, Akihide*; Yagi, Masatoshi*; Iio, Shunji*
Purazuma, Kaku Yugo Gakkai-Shi, 72(12), p.1417 - 1423, 1996/12
no abstracts in English
Kikuchi, Mitsuru; Fasoli, A.*; Takizuka, Tomonori*; Diamond, P.*; Medvedev, S.*; Duan, X.*; Zushi, Hideki*; Furukawa, Masaru*; Kishimoto, Yasuaki*; Wu, Y.*; et al.
no journal, ,
Power and particle control is challenging for standard D-shaped H-mode scenario in tokamak. Possibility of negative triangularity as innovative tokamak concept is discussed by Kikuchi et al. Experimental and numerical studies of negative triangular plasma at CRPP-EPFL success-fully demonstrated improved connement and the weakening of the SOL flow acceleration is implied for the negative triangularity. Recent studies on mechanism of type II and grassy ELM show importance of closure of second stability access to achieve small ELM regimes and also kinetic effects. Medvedev showed that closure of second stability also occurs for negative triangularity. But the MHD stability in negative triangularity is a bit more complicated so that closure of second stability does not imply easy access to small ELM regimes. We discuss critical elements behind.
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.
Nagashima, Yoshihiko*; Ito, Kimitaka*; Ito, Sanae*; Fujisawa, Akihide*; Yagi, Masatoshi*; Hoshino, Katsumichi; Shinohara, Koji; Uehara, Kazuya; Miura, Yukitoshi; Ido, Takeshi*; et al.
no journal, ,
The observation of the zonal flow by the analysis of the density fluctuations is presented. Previously, we have observed the oscillating zonal flow (GAM) by the analysis of the potential fluctuations. This time we took notice of the generation mechanism of the GAM, parametric modulational instability, and analysed the density fluctuation data of the JFT-2M tokamak. By the statistical analysis we found that the biphase of the GAM and turbulence changes its sign according to the direction of the magnetic field in consistent with a drift wave turbulence theory. Also we have first found that the magnitude of the nonlinear interaction can be obtained from the density fluctuation as previously obtained from the potential fluctuations.