Two-dimensional imaging of edge-localized modes in KSTAR plasmas unperturbed and perturbed by n=1 external magnetic fields

Yun, G. S.; Lee, W.; Choi, M.; Lee, J.; Park, H. K.; Domier, Calvin; Luhmann, N. C.; Tobias, Benjamin; Donné, A. J. H.; Lee, J. H.; Jeon, Y.M.; Yoon, S. W.; Team, Kstar

doi:10.1063/1.3694842

Cited by 36 publications

(46 citation statements)

References 24 publications

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“…where α Ã is the pitch angle near the midplane, v ⊥ is the perpendicular plasma flow velocity, and v ph is the phase velocity of mode in the plasma frame [13]. In the rising phase of the RMP current (I RMP ), the amplitude of the ELM crash slightly reduced but the mode number (n ∼ 15) remained the same.…”

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confidence: 99%

Nonlinear Interaction of Edge-Localized Modes and Turbulent Eddies in Toroidal Plasma undern=1Magnetic Perturbation

et al. 2016

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The effect of static n ¼ 1 resonant magnetic perturbation (RMP) on the spatial structure and temporal dynamics of edge-localized modes (ELMs) and edge turbulence in tokamak plasma has been investigated. Two-dimensional images measured by a millimeter-wave camera on the KSTAR tokamak revealed that the coherent filamentary modes (i.e., ELMs) are still present in the edge region when the usual large scale collapse of the edge confinement, i.e., the ELM crash, is completely suppressed by n ¼ 1 RMP. Cross-correlation analyses on the 2D images show that (1) the RMP enhances turbulent fluctuations in the edge toward the ELM-crash-suppression phase, (2) the induced turbulence has a clear dispersion relation for wide ranges of wave number and frequency, and (3) the turbulence involves a net radially outward energy transport. Nonlinear interactions of the turbulent eddies with the coexisting ELMs are clearly observed by bispectral analysis, which implies that the exchange of energy between them may be the key to the prevention of large scale crashes.

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confidence: 99%

Nonlinear Interaction of Edge-Localized Modes and Turbulent Eddies in Toroidal Plasma undern=1Magnetic Perturbation

et al. 2016

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“…5). (3) Alterations of ELM structure and dynamics caused by n=1 magnetic perturbations (MPs) [11] and supersonic molecular beam injection (SMBI) [12] have been measured to study the mechanisms of ELM suppression and mitigation ( Fig. 6) (4) Various modified sawtooth structures different from the normal internal kink [13,14] have been found under electron cyclotron resonance heating (ECRH) conditions (Fig.…”

Section: Summary Of Kstar Ecei Resultsmentioning

confidence: 99%

Visualization of core and edge MHD instabilities in 2D using ECEI

Yun

Lee

Choi

et al. 2012

EPJ Web of Conferences

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Abstract. MHD instabilities in the core and edge of the KSTAR plasmas have been visualized in 2D using an electron cyclotron emission imaging (ECEI) system with sufficient time and space resolutions for the study of the underlying dynamics. In the core region where the ECE optical depth is large, the ECEI has provided localized measurements of fast MHD phenomena such as the crash of internal kinks and coalescence of dual flux tubes. In the edge pedestal region of H-mode plasmas where the optical depth is marginal, the ECEI measurements were found to be still localized and were able to provide detailed 2D images of edge localized modes (ELMs) such as the growth of multiple filamentary structures and the crash of the pedestal characterized by fast localized bursts of the filaments [3]. The effect of electron temperature and density fluctuations on the ECE signals has been analysed to understand the limitations of the edge ECEI measurements.

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“…If there are long-lived coherent modes in the Hmode, exact apparent velocities can be easily determined as demonstrated in Ref. 17. …”

Section: Discussionmentioning

confidence: 99%

“…pedestal of H-mode plasmas (probably due to the slow toroidal rotation in the edge region but large pressure gradient). 17 From Eqs. (4) and (5), it can be understood that the apparent poloidal velocity in the ion diamagnetic direction can be significantly reduced or reversed to the electron diamagnetic direction by the enhanced diamagnetic term in the steep ion pressure region (edge pedestal or internal transport barrier).…”

Section: E 3 B Flow Velocity Deduced From the Apparent Poloidal Rmentioning

confidence: 99%

“…are the turbulence length scales parallel and perpendicular, respectively, to the magnetic field line within the flux surface). The poloidal velocity of the elongated turbulent structures measured by multichannel diagnostics (dubbed as "apparent poloidal velocity" in this paper) is given by 17,18 …”

Section: E 3 B Flow Velocity Deduced From the Apparent Poloidal Rmentioning

confidence: 99%

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E × B flow velocity deduced from the poloidal motion of fluctuation patterns in neutral beam injected L-mode plasmas on KSTAR

et al. 2016

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Articles you may be interested inA method for direct assessment of the equilibrium E Â B flow velocity (E Â B flow shear is responsible for the turbulence suppression and transport reduction in tokamak plasmas) is investigated based on two facts. The first one is that the apparent poloidal rotation speed of density fluctuation patterns is close to the turbulence rotation speed in the direction perpendicular to the local magnetic field line within the flux surface. And the second "well-known" fact is that the turbulence rotation velocity consists of the equilibrium E Â B flow velocity and intrinsic phase velocity of turbulence in the E Â B flow frame. In the core region of the low confinement (L-mode) discharges where a strong toroidal rotation is induced by neutral beam injection, the apparent poloidal velocities (and turbulence rotation velocities) are good approximations of the E Â B flow velocities since linear gyrokinetic simulations suggest that the intrinsic phase velocity of the dominant turbulence is significantly lower than the apparent poloidal velocity. In the neutral beam injected L-mode plasmas, temporal and spatial scales of the measured turbulence are studied by comparing with the local equilibrium parameters relevant to the ion-scale turbulence. Published by AIP Publishing. [http://dx

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Two-dimensional imaging of edge-localized modes in KSTAR plasmas unperturbed and perturbed by n=1 external magnetic fields

Cited by 36 publications

References 24 publications

Nonlinear Interaction of Edge-Localized Modes and Turbulent Eddies in Toroidal Plasma undern=1Magnetic Perturbation

Nonlinear Interaction of Edge-Localized Modes and Turbulent Eddies in Toroidal Plasma undern=1Magnetic Perturbation

Visualization of core and edge MHD instabilities in 2D using ECEI

E × B flow velocity deduced from the poloidal motion of fluctuation patterns in neutral beam injected L-mode plasmas on KSTAR

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