The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform

Sumio Kitajima - One of the best experts on this subject based on the ideXlab platform.

  • Spontaneous L-H transitions under marginal Hot Cathode biasing in the Tohoku University Heliac
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Yokoyama, Shigeru Inagaki, Yasuhiro Suzuki, Kiyohiko Nishimura, M. Ogawa
    Abstract:

    A series of Hot Cathode biasing experiments with marginal conditions for improved mode transition were carried out in the Tohoku University Heliac (TU-Heliac). Spontaneous transitions were observed accompanied by a delay of a few milliseconds. Transition conditions were explored over a wide operation range. The transition points can be identified clearly and easily in the operation range, because the plasma parameters changed slowly until the spontaneous transition. Although operation conditions were spread over a wide range, poloidal Mach numbers for transitions were concentrated in the range of -Mp = 1-2 and normalized driving forces for poloidal rotation agreed well with the local maximum value of ion viscosity predicted by neoclassical theory. The local maximum of ion viscosity against the poloidal Mach number was found to play a key role in the L-H transition. Marginal Hot Cathode biasing is suitable to determine the threshold conditions for the L-H transition.

  • Measurement of fluctuations in the supersonic poloidal flow driven by a Hot Cathode
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, Atsushi Okamoto, K. Shinto, Sumio Kitajima
    Abstract:

    The density and potential fluctuations were measured in Hot-Cathode biasing plasma at the Tohoku University Heliac. In the improved mode, high-frequency fluctuations (> 100 kHz) appeared in the density signal. On the other hand, low-frequency fluctuations (

  • LH transition by a biased Hot Cathode in the Tohoku University Heliac
    Nuclear Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Mamiko Sasao, Hiromi Takahashi, H. Utoh, Shigeru Inagaki, Kiyohiko Nishimura, Masakazu Takayama, M. Yokoyama
    Abstract:

    In the Tohoku University Heliac (TU-Heliac), a helical axis stellarator, an electron injection electrode using a Hot Cathode made of LaB6 was developed and the transition mechanism to an improved mode has been intensively studied. In the electrode current-sweep mode of biasing experiments, a bifurcation phenomenon, i.e. a negative resistance feature in the electrode characteristics was observed accompanied with transition to an improved mode (H-mode) or transition from H-mode to L-mode, in helium plasma discharges of a wide range of collisionality. The ion viscous damping force was estimated from the J ? B driving force for poloidal rotation. The local maxima in viscosity were found at the poloidal Mach number around ?Mp ~ 1?3, as predicted by neoclassical theory. It was also found that the negative resistance (a bifurcation phenomenon) was observed when the poloidal viscosity showed a local maximum.

  • Radial electric field control by biased Hot Cathode in Tohoku University Heliac
    The 30th International Conference on Plasma Science 2003. ICOPS 2003. IEEE Conference Record - Abstracts., 1
    Co-Authors: Sumio Kitajima, H. Takahasi, Y. Tanaka, Hidetoshi Hashizume, Mamiko Sasao
    Abstract:

    Summary form only given, as follows. The influence of a negative biased electrode on the plasma parameters is investigated by using an emissive Hot Cathode made of LaB/sub 6/ in the Tohoku University Heliac. We have already succeeded in inducing the strong negative radial electric field by the negative biased Hot Cathode, which works as an electron source. In order to clarify the radial electric field formation in the heliac system, we attempted the following experiment, (i) radial current control with a constant current power supply, (ii) radial electric field control by the radial current.

Y. Tanaka - One of the best experts on this subject based on the ideXlab platform.

  • Potential and density fluctuation characteristics of the Hot-Cathode-biased supersonic plasma in TU-Heliac
    Fusion Science and Technology, 2007
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, H. Umetsu, Atsushi Okamoto, K. Shinto
    Abstract:

    In the Tohoku University Heliac (TU-Heliac), Hot-Cathode biasing experiment has been carried out. Poloidal Mach number exceeded unity, and reached 5 (supersonic regime). Increase of the electron density and decrease of the impurity influx were observed. It is important to study the anomalous transport for evaluation of the improvement. Then potential and density fluctuation (∼600 kHz) measurement system were installed to the TU-Heliac. Characteristics of the fluctuations in the Hot-Cathode-biased supersonic plasma were measured. The fluctuation of (i) low frequency band (

  • Measurement of fluctuations in the supersonic poloidal flow driven by a Hot Cathode
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, Atsushi Okamoto, K. Shinto, Sumio Kitajima
    Abstract:

    The density and potential fluctuations were measured in Hot-Cathode biasing plasma at the Tohoku University Heliac. In the improved mode, high-frequency fluctuations (> 100 kHz) appeared in the density signal. On the other hand, low-frequency fluctuations (

  • Spontaneous L-H transitions under marginal Hot Cathode biasing in the Tohoku University Heliac
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Yokoyama, Shigeru Inagaki, Yasuhiro Suzuki, Kiyohiko Nishimura, M. Ogawa
    Abstract:

    A series of Hot Cathode biasing experiments with marginal conditions for improved mode transition were carried out in the Tohoku University Heliac (TU-Heliac). Spontaneous transitions were observed accompanied by a delay of a few milliseconds. Transition conditions were explored over a wide operation range. The transition points can be identified clearly and easily in the operation range, because the plasma parameters changed slowly until the spontaneous transition. Although operation conditions were spread over a wide range, poloidal Mach numbers for transitions were concentrated in the range of -Mp = 1-2 and normalized driving forces for poloidal rotation agreed well with the local maximum value of ion viscosity predicted by neoclassical theory. The local maximum of ion viscosity against the poloidal Mach number was found to play a key role in the L-H transition. Marginal Hot Cathode biasing is suitable to determine the threshold conditions for the L-H transition.

  • measurement of fluctuations in the supersonic poloidal flow driven by a Hot Cathode
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, K. Iwazaki, H. Aoyama, Atsushi Okamoto, K. Shinto, Masayuki Ogawa, S Kitajima
    Abstract:

    The density and potential fluctuations were measured in Hot-Cathode biasing plasma at the Tohoku University Heliac. In the improved mode, high-frequency fluctuations (> 100 kHz) appeared in the density signal. On the other hand, low-frequency fluctuations (<100 kHz) in the density and potential signals were suppressed. The characteristics of high-frequency fluctuation were compared with three kinds of instability, and they were consistent with those of the flute instability driven by the supersonic poloidal rotation. The suppression of low-frequency fluctuations in improved mode is considered the effect of E x B poloidal rotation or its shear. The profile of the anomalous particle flux was estimated by analysing the low-frequency fluctuation signals. The flux decreased in the improved mode in most of the region, although the decrease in flux was small near the rational surface (n/m = 5/3).

  • LH transition by a biased Hot Cathode in the Tohoku University Heliac
    Nuclear Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Mamiko Sasao, Hiromi Takahashi, H. Utoh, Shigeru Inagaki, Kiyohiko Nishimura, Masakazu Takayama, M. Yokoyama
    Abstract:

    In the Tohoku University Heliac (TU-Heliac), a helical axis stellarator, an electron injection electrode using a Hot Cathode made of LaB6 was developed and the transition mechanism to an improved mode has been intensively studied. In the electrode current-sweep mode of biasing experiments, a bifurcation phenomenon, i.e. a negative resistance feature in the electrode characteristics was observed accompanied with transition to an improved mode (H-mode) or transition from H-mode to L-mode, in helium plasma discharges of a wide range of collisionality. The ion viscous damping force was estimated from the J ? B driving force for poloidal rotation. The local maxima in viscosity were found at the poloidal Mach number around ?Mp ~ 1?3, as predicted by neoclassical theory. It was also found that the negative resistance (a bifurcation phenomenon) was observed when the poloidal viscosity showed a local maximum.

Hiromi Takahashi - One of the best experts on this subject based on the ideXlab platform.

  • Potential and density fluctuation characteristics of the Hot-Cathode-biased supersonic plasma in TU-Heliac
    Fusion Science and Technology, 2007
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, H. Umetsu, Atsushi Okamoto, K. Shinto
    Abstract:

    In the Tohoku University Heliac (TU-Heliac), Hot-Cathode biasing experiment has been carried out. Poloidal Mach number exceeded unity, and reached 5 (supersonic regime). Increase of the electron density and decrease of the impurity influx were observed. It is important to study the anomalous transport for evaluation of the improvement. Then potential and density fluctuation (∼600 kHz) measurement system were installed to the TU-Heliac. Characteristics of the fluctuations in the Hot-Cathode-biased supersonic plasma were measured. The fluctuation of (i) low frequency band (

  • Measurement of fluctuations in the supersonic poloidal flow driven by a Hot Cathode
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, Atsushi Okamoto, K. Shinto, Sumio Kitajima
    Abstract:

    The density and potential fluctuations were measured in Hot-Cathode biasing plasma at the Tohoku University Heliac. In the improved mode, high-frequency fluctuations (> 100 kHz) appeared in the density signal. On the other hand, low-frequency fluctuations (

  • Spontaneous L-H transitions under marginal Hot Cathode biasing in the Tohoku University Heliac
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Yokoyama, Shigeru Inagaki, Yasuhiro Suzuki, Kiyohiko Nishimura, M. Ogawa
    Abstract:

    A series of Hot Cathode biasing experiments with marginal conditions for improved mode transition were carried out in the Tohoku University Heliac (TU-Heliac). Spontaneous transitions were observed accompanied by a delay of a few milliseconds. Transition conditions were explored over a wide operation range. The transition points can be identified clearly and easily in the operation range, because the plasma parameters changed slowly until the spontaneous transition. Although operation conditions were spread over a wide range, poloidal Mach numbers for transitions were concentrated in the range of -Mp = 1-2 and normalized driving forces for poloidal rotation agreed well with the local maximum value of ion viscosity predicted by neoclassical theory. The local maximum of ion viscosity against the poloidal Mach number was found to play a key role in the L-H transition. Marginal Hot Cathode biasing is suitable to determine the threshold conditions for the L-H transition.

  • measurement of fluctuations in the supersonic poloidal flow driven by a Hot Cathode
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, K. Iwazaki, H. Aoyama, Atsushi Okamoto, K. Shinto, Masayuki Ogawa, S Kitajima
    Abstract:

    The density and potential fluctuations were measured in Hot-Cathode biasing plasma at the Tohoku University Heliac. In the improved mode, high-frequency fluctuations (> 100 kHz) appeared in the density signal. On the other hand, low-frequency fluctuations (<100 kHz) in the density and potential signals were suppressed. The characteristics of high-frequency fluctuation were compared with three kinds of instability, and they were consistent with those of the flute instability driven by the supersonic poloidal rotation. The suppression of low-frequency fluctuations in improved mode is considered the effect of E x B poloidal rotation or its shear. The profile of the anomalous particle flux was estimated by analysing the low-frequency fluctuation signals. The flux decreased in the improved mode in most of the region, although the decrease in flux was small near the rational surface (n/m = 5/3).

  • LH transition by a biased Hot Cathode in the Tohoku University Heliac
    Nuclear Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Mamiko Sasao, Hiromi Takahashi, H. Utoh, Shigeru Inagaki, Kiyohiko Nishimura, Masakazu Takayama, M. Yokoyama
    Abstract:

    In the Tohoku University Heliac (TU-Heliac), a helical axis stellarator, an electron injection electrode using a Hot Cathode made of LaB6 was developed and the transition mechanism to an improved mode has been intensively studied. In the electrode current-sweep mode of biasing experiments, a bifurcation phenomenon, i.e. a negative resistance feature in the electrode characteristics was observed accompanied with transition to an improved mode (H-mode) or transition from H-mode to L-mode, in helium plasma discharges of a wide range of collisionality. The ion viscous damping force was estimated from the J ? B driving force for poloidal rotation. The local maxima in viscosity were found at the poloidal Mach number around ?Mp ~ 1?3, as predicted by neoclassical theory. It was also found that the negative resistance (a bifurcation phenomenon) was observed when the poloidal viscosity showed a local maximum.

H. Utoh - One of the best experts on this subject based on the ideXlab platform.

  • Potential and density fluctuation characteristics of the Hot-Cathode-biased supersonic plasma in TU-Heliac
    Fusion Science and Technology, 2007
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, H. Umetsu, Atsushi Okamoto, K. Shinto
    Abstract:

    In the Tohoku University Heliac (TU-Heliac), Hot-Cathode biasing experiment has been carried out. Poloidal Mach number exceeded unity, and reached 5 (supersonic regime). Increase of the electron density and decrease of the impurity influx were observed. It is important to study the anomalous transport for evaluation of the improvement. Then potential and density fluctuation (∼600 kHz) measurement system were installed to the TU-Heliac. Characteristics of the fluctuations in the Hot-Cathode-biased supersonic plasma were measured. The fluctuation of (i) low frequency band (

  • Measurement of fluctuations in the supersonic poloidal flow driven by a Hot Cathode
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, Atsushi Okamoto, K. Shinto, Sumio Kitajima
    Abstract:

    The density and potential fluctuations were measured in Hot-Cathode biasing plasma at the Tohoku University Heliac. In the improved mode, high-frequency fluctuations (> 100 kHz) appeared in the density signal. On the other hand, low-frequency fluctuations (

  • Spontaneous L-H transitions under marginal Hot Cathode biasing in the Tohoku University Heliac
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Yokoyama, Shigeru Inagaki, Yasuhiro Suzuki, Kiyohiko Nishimura, M. Ogawa
    Abstract:

    A series of Hot Cathode biasing experiments with marginal conditions for improved mode transition were carried out in the Tohoku University Heliac (TU-Heliac). Spontaneous transitions were observed accompanied by a delay of a few milliseconds. Transition conditions were explored over a wide operation range. The transition points can be identified clearly and easily in the operation range, because the plasma parameters changed slowly until the spontaneous transition. Although operation conditions were spread over a wide range, poloidal Mach numbers for transitions were concentrated in the range of -Mp = 1-2 and normalized driving forces for poloidal rotation agreed well with the local maximum value of ion viscosity predicted by neoclassical theory. The local maximum of ion viscosity against the poloidal Mach number was found to play a key role in the L-H transition. Marginal Hot Cathode biasing is suitable to determine the threshold conditions for the L-H transition.

  • measurement of fluctuations in the supersonic poloidal flow driven by a Hot Cathode
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, K. Iwazaki, H. Aoyama, Atsushi Okamoto, K. Shinto, Masayuki Ogawa, S Kitajima
    Abstract:

    The density and potential fluctuations were measured in Hot-Cathode biasing plasma at the Tohoku University Heliac. In the improved mode, high-frequency fluctuations (> 100 kHz) appeared in the density signal. On the other hand, low-frequency fluctuations (<100 kHz) in the density and potential signals were suppressed. The characteristics of high-frequency fluctuation were compared with three kinds of instability, and they were consistent with those of the flute instability driven by the supersonic poloidal rotation. The suppression of low-frequency fluctuations in improved mode is considered the effect of E x B poloidal rotation or its shear. The profile of the anomalous particle flux was estimated by analysing the low-frequency fluctuation signals. The flux decreased in the improved mode in most of the region, although the decrease in flux was small near the rational surface (n/m = 5/3).

  • LH transition by a biased Hot Cathode in the Tohoku University Heliac
    Nuclear Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Mamiko Sasao, Hiromi Takahashi, H. Utoh, Shigeru Inagaki, Kiyohiko Nishimura, Masakazu Takayama, M. Yokoyama
    Abstract:

    In the Tohoku University Heliac (TU-Heliac), a helical axis stellarator, an electron injection electrode using a Hot Cathode made of LaB6 was developed and the transition mechanism to an improved mode has been intensively studied. In the electrode current-sweep mode of biasing experiments, a bifurcation phenomenon, i.e. a negative resistance feature in the electrode characteristics was observed accompanied with transition to an improved mode (H-mode) or transition from H-mode to L-mode, in helium plasma discharges of a wide range of collisionality. The ion viscous damping force was estimated from the J ? B driving force for poloidal rotation. The local maxima in viscosity were found at the poloidal Mach number around ?Mp ~ 1?3, as predicted by neoclassical theory. It was also found that the negative resistance (a bifurcation phenomenon) was observed when the poloidal viscosity showed a local maximum.

M. Ogawa - One of the best experts on this subject based on the ideXlab platform.

  • Potential and density fluctuation characteristics of the Hot-Cathode-biased supersonic plasma in TU-Heliac
    Fusion Science and Technology, 2007
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, H. Umetsu, Atsushi Okamoto, K. Shinto
    Abstract:

    In the Tohoku University Heliac (TU-Heliac), Hot-Cathode biasing experiment has been carried out. Poloidal Mach number exceeded unity, and reached 5 (supersonic regime). Increase of the electron density and decrease of the impurity influx were observed. It is important to study the anomalous transport for evaluation of the improvement. Then potential and density fluctuation (∼600 kHz) measurement system were installed to the TU-Heliac. Characteristics of the fluctuations in the Hot-Cathode-biased supersonic plasma were measured. The fluctuation of (i) low frequency band (

  • Measurement of fluctuations in the supersonic poloidal flow driven by a Hot Cathode
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Ogawa, K. Iwazaki, H. Aoyama, Atsushi Okamoto, K. Shinto, Sumio Kitajima
    Abstract:

    The density and potential fluctuations were measured in Hot-Cathode biasing plasma at the Tohoku University Heliac. In the improved mode, high-frequency fluctuations (> 100 kHz) appeared in the density signal. On the other hand, low-frequency fluctuations (

  • Spontaneous L-H transitions under marginal Hot Cathode biasing in the Tohoku University Heliac
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Sumio Kitajima, Y. Tanaka, Hiromi Takahashi, H. Utoh, J. Shinde, M. Yokoyama, Shigeru Inagaki, Yasuhiro Suzuki, Kiyohiko Nishimura, M. Ogawa
    Abstract:

    A series of Hot Cathode biasing experiments with marginal conditions for improved mode transition were carried out in the Tohoku University Heliac (TU-Heliac). Spontaneous transitions were observed accompanied by a delay of a few milliseconds. Transition conditions were explored over a wide operation range. The transition points can be identified clearly and easily in the operation range, because the plasma parameters changed slowly until the spontaneous transition. Although operation conditions were spread over a wide range, poloidal Mach numbers for transitions were concentrated in the range of -Mp = 1-2 and normalized driving forces for poloidal rotation agreed well with the local maximum value of ion viscosity predicted by neoclassical theory. The local maximum of ion viscosity against the poloidal Mach number was found to play a key role in the L-H transition. Marginal Hot Cathode biasing is suitable to determine the threshold conditions for the L-H transition.