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Your search keyword '"Nagashima, Y."' showing total 22 results
Start Over Author "Nagashima, Y." Journal physics of plasmas
22 results on '"Nagashima, Y."'

1. Non-Gaussian properties of global momentum and particle fluxes in a cylindrical laboratory plasma

Author

Nagashima, Y, Itoh, SI, Inagaki, S, Arakawa, H, Kasuya, N, Fujisawa, A, Kamataki, K, Yamada, T, Shinohara, S, Oldenbürger, S, Yagi, M, Takase, Y, Diamond, PH, and Itoh, K

Subjects
Fluids & Plasmas, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Classical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Non-Gaussian statistical properties of the azimuthally averaged momentum and particle fluxes driven by turbulence have been simultaneously observed in inhomogeneous magnetized plasmas for the first time. We identified the stretched Gaussian distribution of the both fluxes and the transition from the point-wise distribution to averaged ones was confirmed. The change of the particle flux precedes that of the momentum flux, demonstrating that the momentum flux is induced by the relaxation of density gradient. © 2011 American Institute of Physics.

Published
2011

2. Observation of the parametric-modulational instability between the drift-wave fluctuation and azimuthally symmetric sheared radial electric field oscillation in a cylindrical laboratory plasma

Author

Nagashima, Y, Itoh, SI, Shinohara, S, Fukao, M, Fujisawa, A, Terasaka, K, Kawai, Y, Tynan, GR, Diamond, PH, Yagi, M, Inagaki, S, Yamada, T, and Itoh, K

Subjects
modulational instability, parametric instability, plasma drift waves, plasma fluctuations, plasma nonlinear processes, plasma oscillations, Fluids & Plasmas, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Classical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Observation of the parametric-modulational interaction between the drift-wave fluctuation (7-8 kHz) and azimuthally symmetric sheared radial electric field structure (∼0.4 kHz) in a cylindrical laboratory plasma is presented. Oscillation of the sheared radial electric field is synchronized at modulations of the radial wave number and Reynolds stress per mass density of the drift-wave spectrum. Bispectral analysis at the location where the sheared radial electric field has finite radial wave numbers shows that nonlinear energy transfers from the drift wave to the sheared radial electric field occur. Nonlocal energy transfers of fluctuations via "channel of the azimuthally symmetric sheared radial electric field" in spectral space as well as real space are discovered. © 2009 American Institute of Physics.

Published
2009

3. Experimental studies of zonal flow and field in compact helical system plasma

Author

Fujisawa, A, Itoh, K, Shimizu, A, Nakano, H, Ohshima, S, Iguchi, H, Matsuoka, K, Okamura, S, Minami, T, Yoshimura, Y, Nagaoka, K, Ida, K, Toi, K, Takahashi, C, Kojima, M, Nishimura, S, Isobe, M, Suzuki, C, Akiyama, T, Ido, T, Nagashima, Y, Itoh, SI, and Diamond, PH

Subjects
Fluids & Plasmas, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Classical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

The experimental studies on zonal flows and turbulence have been carried out in Compact Helical System [K. Matsuoka, S. Kubo, M. Hosokawa, in Plasma Physics and Controlled Nuclear Fusion Research, Proc. 12th Int. Conf., Nice, 1988 (International Atomic Energy Agency, Vienna, 1989, Vol. 2, p. 411] using twin heavy ion beam probes. The paper presents the experimental observations of stationary zonal flow, nonlinear couplings between zonal flow and turbulence, and the role of zonal flow in the improved confinement, together with the recent discovery of zonal magnetic field. The presented experimental results strongly support the new paradigm that the plasma transport should be considered as a system of drift wave and zonal flows, and provides the first direct evidence for turbulence dynamo that the structured magnetic field can be really generated by turbulence. © 2008 American Institute of Physics.

Published
2008

4. Physics of zonal flowsa)

Author

Itoh, K, Itoh, S-I, Diamond, PH, Hahm, TS, Fujisawa, A, Tynan, GR, Yagi, M, and Nagashima, Y

Subjects
Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Classical Physics, Fluids & Plasmas
Abstract

Zonal flows, which means azimuthally symmetric band-like shear flows, are ubiquitous phenomena in nature and the laboratory. It is now widely recognized that zonal flows are a key constituent in virtually all cases and regimes of drift wave turbulence, indeed, so much so that this classic problem is now frequently referred to as "drift wave-zonal flow turbulence." In this review, new viewpoints and unifying concepts are presented, which facilitate understanding of zonal flow physics, via theory, computation and their confrontation with the results of laboratory experiment. Special emphasis is placed on identifying avenues for further progress. © 2006 American Institute of Physics.

Published
2006

5. On the bicoherence analysis of plasma turbulence

Author

Itoh, K, Nagashima, Y, Itoh, SI, Diamond, PH, Fujisawa, A, Yagi, M, and Fukuyama, A

Subjects
Fluids & Plasmas, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Classical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

The bicoherence of fluctuations in a system of drift waves and zonal flows is discussed. In strong drift-wave turbulence, where broadband fluctuations are excited, the bicoherence is examined. A Langevin equation formalism of turbulent interactions allows us to relate the bicoherence coefficient to the projection of nonlinear force onto the test mode. The dependence of the summed bicoherence on the amplitude of zonal flows is clarified. The importance of observing biphase is also stressed. The results provide a basis for measurement of nonlinear interaction in a system of drift waves and zonal flow. © 2005 American Institute of Physics.

Published
2005

8. Observations of radially elongated particle flux induced by streamer in a linear magnetized plasma

Author

Kin, F., primary, Fujisawa, A., additional, Itoh, K., additional, Kosuga, Y., additional, Sasaki, M., additional, Inagaki, S., additional, Nagashima, Y., additional, Yamada, T., additional, Kasuya, N., additional, Yamasaki, K., additional, Hasamada, K., additional, Zhang, B. Y., additional, Kawachi, Y., additional, Arakawa, H., additional, Kobayashi, T., additional, and Itoh, S.-I., additional

Published
2019
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10. Extraction of nonlinear waveform in turbulent plasma

Author

Kin, F., primary, Itoh, K., additional, Fujisawa, A., additional, Kosuga, Y., additional, Sasaki, M., additional, Yamada, T., additional, Inagaki, S., additional, Itoh, S.-I., additional, Kobayashi, T., additional, Nagashima, Y., additional, Kasuya, N., additional, Arakawa, H., additional, Yamasaki, K., additional, and Hasamada, K., additional

Published
2018
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12. Measurements of edge plasma parameters during internal reconnection events in the TST-2 spherical tokamak

Author

Furui, H., primary, Ejiri, A., additional, Nagashima, Y., additional, Takase, Y., additional, Sonehara, M., additional, Tsujii, N., additional, Roidl, B., additional, Shinya, T., additional, Togashi, H., additional, Homma, H., additional, Nakamura, K., additional, Takeuchi, T., additional, Yajima, S., additional, Yoshida, Y., additional, Toida, K., additional, Takahashi, W., additional, and Yamazaki, H., additional

Published
2017
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14. Observation of an edge coherent mode and poloidal flow in the electron cyclotron wave induced high βp plasma in QUEST

Author

Banerjee, Santanu, primary, Zushi, H., additional, Nishino, N., additional, Mishra, K., additional, Mahira, Y., additional, Tashima, S., additional, Ejiri, A., additional, Yamaguchi, T., additional, Onchi, T., additional, Nagashima, Y., additional, Hanada, K., additional, Nakamura, K., additional, Idei, H., additional, Hasegawa, M., additional, Fujisawa, A., additional, Kuzmin, A., additional, and Matsuoka, K., additional

Published
2016
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16. Heat flux and plasma flow in the far scrape-off layer of the inboard poloidal field null configuration in QUEST

Author

Onchi, T., primary, Zushi, H., additional, Mishra, K., additional, Mahira, Y., additional, Nagaoka, K., additional, Hanada, K., additional, Idei, H., additional, Hasegawa, M., additional, Nakamura, K., additional, Fujisawa, A., additional, Nagashima, Y., additional, Matsuoka, K., additional, Tashima, S., additional, Banerjee, S., additional, Kuzmin, A., additional, Kawasaki, S., additional, Nakashima, H., additional, Higashijima, A., additional, and Watanabe, O., additional

Published
2015
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17. Role of stochasticity in turbulence and convective intermittent transport at the scrape off layer of Ohmic plasma in QUEST

Author

Banerjee, Santanu, primary, Zushi, H., additional, Nishino, N., additional, Hanada, K., additional, Ishiguro, M., additional, Tashima, S., additional, Liu, H. Q., additional, Mishra, K., additional, Nakamura, K., additional, Idei, H., additional, Hasegawa, M., additional, Fujisawa, A., additional, Nagashima, Y., additional, and Matsuoka, K., additional

Published
2014
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18. Observation of an edge coherent mode and poloidal flow in the electron cyclotron wave induced high βp plasma in QUEST.

Author

Banerjee, Santanu, Zushi, H., Nishino, N., Mishra, K., Mahira, Y., Tashima, S., Ejiri, A., Yamaguchi, T., Onchi, T., Nagashima, Y., Hanada, K., Nakamura, K., Idei, H., Hasegawa, M., Fujisawa, A., Kuzmin, A., and Matsuoka, K.

Subjects
CYCLOTRON resonance, PLASMA gases, COHERENCE (Nuclear physics), OHMIC contacts, TOKAMAKS
Abstract

Fluctuations are measured in the edge and scrape-off layer (SOL) of QUEST using fast visible imaging diagnostic. Electron cyclotron wave injection in the Ohmic plasma features excitation of low frequency coherent fluctuations near the separatrix and enhanced cross-field transport. Plasma shifts from initial high field side limiter bound (inboard limited, IL) towards inboard poloidal null (IPN) configuration with steepening of the density profile at the edge. This may have facilitated the increased edge and SOL fluctuation activities. Observation of the coherent mode, associated plasma flow, and particle out-flux, for the first time in the IPN plasma configuration in a spherical tokamak may provide further impetus to the edge and SOL turbulence studies in tokamaks. [ABSTRACT FROM AUTHOR]

Published
2016
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22. Reduction effect of neutral density on the excitation of turbulent drift waves in a linear magnetized plasma with flow

Author

Saitou, Y., primary, Yonesu, A., additional, Shinohara, S., additional, Ignatenko, M. V., additional, Kasuya, N., additional, Kawaguchi, M., additional, Terasaka, K., additional, Nishijima, T., additional, Nagashima, Y., additional, Kawai, Y., additional, Yagi, M., additional, Itoh, S.-I., additional, Azumi, M., additional, and Itoh, K., additional

Published
2007
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