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Ye Pang - One of the best experts on this subject based on the ideXlab platform.

  • themis observation of multiple dipolarization fronts and associated wave characteristics in the near earth magnetotail
    Geophysical Research Letters, 2009
    Co-Authors: M Zhou, Maha Ashourabdalla, X H Deng, David Schriver, M Elalaoui, Ye Pang
    Abstract:

    [1] Multiple dipolarization fronts were observed by THEMIS spacecraft in the near-Earth magnetotail during a substorm. The dipolarization fronts were located at the leading edge of earthward propagating plasma bubbles. Major energetic electron flux enhancements were observed at the dipolarization fronts, which were also associated with large wave fluctuations extending from below the lower hybrid frequency to above the electron cyclotron frequency. Intense electric field wave packets, primarily contributed by the Hall electric field and lower hybrid drift (LHD) wave, were observed right at the front, which was a thin current layer with size of the order of the ion inertial length. The LHD wave was believed to be generated by a diamagnetic current in the presence of density and temperature gradients. Electrostatic electron cyclotron harmonic (ECH) waves were detected slightly after the front. The ECH waves were probably generated by the positive slope of the electron Perpendicular Velocity distribution. Both of these waves are suggested to be able to heat electrons. The observation of these waves at the dipolarization front could be important for the understanding of electron energization during substorm injection, as well as the mechanism of current disruption.

  • themis observation of multiple dipolarization fronts and associated wave characteristics in the near earth magnetotail
    Geophysical Research Letters, 2009
    Co-Authors: M Zhou, Maha Ashourabdalla, David Schriver, M Elalaoui, Ye Pang, Xiaohua Deng
    Abstract:

    [1] Multiple dipolarization fronts were observed by THEMIS spacecraft in the near-Earth magnetotail during a substorm. The dipolarization fronts were located at the leading edge of earthward propagating plasma bubbles. Major energetic electron flux enhancements were observed at the dipolarization fronts, which were also associated with large wave fluctuations extending from below the lower hybrid frequency to above the electron cyclotron frequency. Intense electric field wave packets, primarily contributed by the Hall electric field and lower hybrid drift (LHD) wave, were observed right at the front, which was a thin current layer with size of the order of the ion inertial length. The LHD wave was believed to be generated by a diamagnetic current in the presence of density and temperature gradients. Electrostatic electron cyclotron harmonic (ECH) waves were detected slightly after the front. The ECH waves were probably generated by the positive slope of the electron Perpendicular Velocity distribution. Both of these waves are suggested to be able to heat electrons. The observation of these waves at the dipolarization front could be important for the understanding of electron energization during substorm injection, as well as the mechanism of current disruption.

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

  • themis observation of multiple dipolarization fronts and associated wave characteristics in the near earth magnetotail
    Geophysical Research Letters, 2009
    Co-Authors: M Zhou, Maha Ashourabdalla, X H Deng, David Schriver, M Elalaoui, Ye Pang
    Abstract:

    [1] Multiple dipolarization fronts were observed by THEMIS spacecraft in the near-Earth magnetotail during a substorm. The dipolarization fronts were located at the leading edge of earthward propagating plasma bubbles. Major energetic electron flux enhancements were observed at the dipolarization fronts, which were also associated with large wave fluctuations extending from below the lower hybrid frequency to above the electron cyclotron frequency. Intense electric field wave packets, primarily contributed by the Hall electric field and lower hybrid drift (LHD) wave, were observed right at the front, which was a thin current layer with size of the order of the ion inertial length. The LHD wave was believed to be generated by a diamagnetic current in the presence of density and temperature gradients. Electrostatic electron cyclotron harmonic (ECH) waves were detected slightly after the front. The ECH waves were probably generated by the positive slope of the electron Perpendicular Velocity distribution. Both of these waves are suggested to be able to heat electrons. The observation of these waves at the dipolarization front could be important for the understanding of electron energization during substorm injection, as well as the mechanism of current disruption.

  • themis observation of multiple dipolarization fronts and associated wave characteristics in the near earth magnetotail
    Geophysical Research Letters, 2009
    Co-Authors: M Zhou, Maha Ashourabdalla, David Schriver, M Elalaoui, Ye Pang, Xiaohua Deng
    Abstract:

    [1] Multiple dipolarization fronts were observed by THEMIS spacecraft in the near-Earth magnetotail during a substorm. The dipolarization fronts were located at the leading edge of earthward propagating plasma bubbles. Major energetic electron flux enhancements were observed at the dipolarization fronts, which were also associated with large wave fluctuations extending from below the lower hybrid frequency to above the electron cyclotron frequency. Intense electric field wave packets, primarily contributed by the Hall electric field and lower hybrid drift (LHD) wave, were observed right at the front, which was a thin current layer with size of the order of the ion inertial length. The LHD wave was believed to be generated by a diamagnetic current in the presence of density and temperature gradients. Electrostatic electron cyclotron harmonic (ECH) waves were detected slightly after the front. The ECH waves were probably generated by the positive slope of the electron Perpendicular Velocity distribution. Both of these waves are suggested to be able to heat electrons. The observation of these waves at the dipolarization front could be important for the understanding of electron energization during substorm injection, as well as the mechanism of current disruption.

T Estrada - One of the best experts on this subject based on the ideXlab platform.

  • doppler reflectometer system in the stellarator tj ii
    Review of Scientific Instruments, 2009
    Co-Authors: T Happel, T Estrada, E Blanco, V Tribaldos, A Cappa, A Bustos
    Abstract:

    A Doppler reflectometer system has recently been installed in the stellarator TJ-II. The system is optimized for the Q-band (33–50 GHz) and the high-curvature plasmas produced in TJ-II. The launch angle of the microwave beam can be controlled by a steerable mirror to obtain angles between ±20° enabling the measurement of Perpendicular wave numbers in the range of 3–15 cm−1. The available angular range allows for comparisons between positive and negative values and additionally for calibration of the system. Localization and k⊥-estimation is done via the three-dimensional ray/beam-tracing code TRUBA. First measured spectra and radial profiles of the Perpendicular Velocity of plasma density fluctuations are presented.

  • doppler reflectometer system in the stellarator tj ii
    Review of Scientific Instruments, 2009
    Co-Authors: T Happel, T Estrada, E Blanco, V Tribaldos, A Cappa, A Bustos
    Abstract:

    A Doppler reflectometer system has recently been installed in the stellarator TJ-II. The system is optimized for the Q-band (33-50 GHz) and the high-curvature plasmas produced in TJ-II. The launch angle of the microwave beam can be controlled by a steerable mirror to obtain angles between +/-20 degrees enabling the measurement of Perpendicular wave numbers in the range of 3-15 cm(-1). The available angular range allows for comparisons between positive and negative values and additionally for calibration of the system. Localization and k(Perpendicular)-estimation is done via the three-dimensional ray/beam-tracing code TRUBA. First measured spectra and radial profiles of the Perpendicular Velocity of plasma density fluctuations are presented.

  • parametric dependence of the Perpendicular Velocity shear layer formation in tj ii plasmas
    Plasma and Fusion Research, 2008
    Co-Authors: L Guimarais, T Happel, T Estrada, E Blanco, E Ascasibar, M Manso, L Cupido, Francisco Castejon, R Jimenezgomez, Maria A Pedrosa
    Abstract:

    In TJ-II plasmas, the Perpendicular rotation Velocity of the turbulence changes from positive to negative (from ion to electron diamagnetic direction) inside the Last Closed Magnetic Surface (LCMS) when the lineaveraged plasma density exceeds some critical value, this change being dominated by the inversion in the radial electric field. In this work we study the parameters that control the inversion in the Perpendicular rotation. A parametric dependence of the critical density has been obtained studying plasmas confined in different magnetic configurations (different rotational transform and/or plasma volume) and heated with different ECH power levels. The studied data set shows a positive exponential dependence on heating power and a negative one on plasma radius, while the dependence on rotational transform has low statistical meaning. Besides, analysis of local plasma parameters points to plasma collisionality as the parameter that controls the inversion of the Perpendicular rotation Velocity of the turbulence.

  • study of doppler reflectometry capability to determine the Perpendicular Velocity and the k spectrum of the density fluctuations using a 2d full wave code
    Plasma Physics and Controlled Fusion, 2008
    Co-Authors: E Blanco, T Estrada
    Abstract:

    The capability of Doppler reflectometry to determine the Perpendicular Velocity and the Perpendicular wave-number spectrum of the density fluctuations has been studied using a two-dimensional full-wave code. The numerical results show that the Perpendicular Velocity of the density fluctuations can be obtained with high accuracy for broad ranges of antenna tilt angles, turbulence levels and radial correlation lengths of the density fluctuations. The diagnostic potential of Doppler reflectometry to determine the Perpendicular wave-number spectrum of the density fluctuations depends on the reflectometer response at different probed wave numbers and different turbulence levels. A linear dependence between the scattered wave amplitude and the turbulence level has been found for low turbulence levels and short radial correlation lengths of the density fluctuations, whereas at high turbulence levels and/or large radial correlation lengths the relationship becomes non-linear. In addition, numerical results show that the reflectometer response depends only very slightly on the probed wave number.

T Happel - One of the best experts on this subject based on the ideXlab platform.

  • poloidally resolved measurements of the Perpendicular propagation Velocity of density fluctuations in asdex upgrade l mode plasmas
    Plasma Physics and Controlled Fusion, 2021
    Co-Authors: K Hofler, T Happel, U Stroth, P Hennequin, M Cavedon, R Dux, R Fischer, R M Mcdermott, E Poli, C Schuster
    Abstract:

    Poloidal asymmetries of the propagation Velocity of density fluctuations Perpendicular to the magnetic field measured with Doppler reflectometry have been reported in several magnetic confinement plasma devices. Careful analysis of a large variety of different low confinement mode plasma scenarios performed at the ASDEX Upgrade tokamak does not reveal such an asymmetry outside the uncertainties of the evaluation process of the measurement data. The Perpendicular Velocity is investigated between mid-radius and the plasma edge and follows the poloidal dependence of the E × B drift Velocity regardless of the probed turbulence structure size. Compared to measurements of a charge exchange recombination spectroscopy diagnostic this points towards a significantly smaller phase Velocity than the E × B drift Velocity. The analysis technique is presented in a representative discharge together with a sensitivity study of the impact of density, magneto hydrodynamic equilibrium and diagnostic alignment on the interpretation of the measured Doppler shift using ray tracing and thus on poloidal asymmetries. Three more highly different plasma scenarios with poloidally symmetric Velocity profiles are shown.

  • magnetic field pitch angle and Perpendicular Velocity measurements from multi point time delay estimation of poloidal correlation reflectometry
    Plasma Physics and Controlled Fusion, 2017
    Co-Authors: D Prisiazhniuk, G D Conway, T Happel, A Kramerflecken, A Lebschy, P Manz, V Nikolaeva, U Stroth
    Abstract:

    In fusion machines, turbulent eddies are expected to be aligned with the direction of the magnetic field lines and to propagate in the Perpendicular direction. Time delay measurements of density fluctuations can be used to calculate the magnetic field pitch angle α and Perpendicular Velocity profiles. The method is applied to poloidal correlation reflectometry installed at ASDEX Upgrade and TEXTOR, which measure density fluctuations from poloidally and toroidally separated antennas. Validation of the method is achieved by comparing the Perpendicular Velocity (composed of the drift and the phase Velocity of turbulence ) with Doppler reflectometry measurements and with neoclassical calculations. An important condition for the application of the method is the presence of turbulence with a sufficiently long decorrelation time. It is shown that at the shear layer the decorrelation time is reduced, limiting the application of the method. The magnetic field pitch angle measured by this method shows the expected dependence on the magnetic field, plasma current and radial position. The profile of the pitch angle reproduces the expected shape and values. However, comparison with the equilibrium reconstruction code cliste suggests an additional inclination of turbulent eddies at the pedestal position (2–3°). This additional angle decreases towards the core and at the edge.

  • doppler reflectometer system in the stellarator tj ii
    Review of Scientific Instruments, 2009
    Co-Authors: T Happel, T Estrada, E Blanco, V Tribaldos, A Cappa, A Bustos
    Abstract:

    A Doppler reflectometer system has recently been installed in the stellarator TJ-II. The system is optimized for the Q-band (33–50 GHz) and the high-curvature plasmas produced in TJ-II. The launch angle of the microwave beam can be controlled by a steerable mirror to obtain angles between ±20° enabling the measurement of Perpendicular wave numbers in the range of 3–15 cm−1. The available angular range allows for comparisons between positive and negative values and additionally for calibration of the system. Localization and k⊥-estimation is done via the three-dimensional ray/beam-tracing code TRUBA. First measured spectra and radial profiles of the Perpendicular Velocity of plasma density fluctuations are presented.

  • doppler reflectometer system in the stellarator tj ii
    Review of Scientific Instruments, 2009
    Co-Authors: T Happel, T Estrada, E Blanco, V Tribaldos, A Cappa, A Bustos
    Abstract:

    A Doppler reflectometer system has recently been installed in the stellarator TJ-II. The system is optimized for the Q-band (33-50 GHz) and the high-curvature plasmas produced in TJ-II. The launch angle of the microwave beam can be controlled by a steerable mirror to obtain angles between +/-20 degrees enabling the measurement of Perpendicular wave numbers in the range of 3-15 cm(-1). The available angular range allows for comparisons between positive and negative values and additionally for calibration of the system. Localization and k(Perpendicular)-estimation is done via the three-dimensional ray/beam-tracing code TRUBA. First measured spectra and radial profiles of the Perpendicular Velocity of plasma density fluctuations are presented.

  • parametric dependence of the Perpendicular Velocity shear layer formation in tj ii plasmas
    Plasma and Fusion Research, 2008
    Co-Authors: L Guimarais, T Happel, T Estrada, E Blanco, E Ascasibar, M Manso, L Cupido, Francisco Castejon, R Jimenezgomez, Maria A Pedrosa
    Abstract:

    In TJ-II plasmas, the Perpendicular rotation Velocity of the turbulence changes from positive to negative (from ion to electron diamagnetic direction) inside the Last Closed Magnetic Surface (LCMS) when the lineaveraged plasma density exceeds some critical value, this change being dominated by the inversion in the radial electric field. In this work we study the parameters that control the inversion in the Perpendicular rotation. A parametric dependence of the critical density has been obtained studying plasmas confined in different magnetic configurations (different rotational transform and/or plasma volume) and heated with different ECH power levels. The studied data set shows a positive exponential dependence on heating power and a negative one on plasma radius, while the dependence on rotational transform has low statistical meaning. Besides, analysis of local plasma parameters points to plasma collisionality as the parameter that controls the inversion of the Perpendicular rotation Velocity of the turbulence.

Weihao Liu - One of the best experts on this subject based on the ideXlab platform.

  • study of the effects of the Perpendicular Velocity gradient on a doppler backscattering system using a 2d full wave code
    Physics of Plasmas, 2017
    Co-Authors: M Y Wang, C Zhou, A D Liu, Xiang Zhang, T Lan, J L Xie, W X Ding, Weihao Liu
    Abstract:

    Doppler backscattering is a powerful diagnostic technique that is used to perform turbulence measurements in magnetic confinement devices. The effects of the Perpendicular Velocity distribution on a Doppler backscattering system are studied using a 2D full wave code, in which the finite-difference time-domain method is used to solve Maxwell's equations. A constant Velocity and several different Velocity gradients are considered, along with a wide range of density fluctuation levels. The numerical results show that the Doppler backscattering mainly occurs around the cut-off layer, and that it has a linear response to turbulence when the fluctuation level is low. However, at higher density fluctuation levels, nonlinear effects become important, and the influence of the area outside the cut-off layer becomes significant. The Velocity gradient causes the backscattering spectrum to become non-Gaussian and asymmetrical; this effect has also been noticed in experiments in the Experimental Advanced Superconductin...