Nonlinear energy transfer from low frequency electromagnetic fluctuations to broadband turbulence during edge localized mode crashes

Kim, Jaewook; Choi, M.; Nam, Y. U.; Jhang, Hogun; Bak, J. G.; Hahn, S.H.; Sung, C.; Choe, Wonho; Ghim, Young-chul

doi:10.1088/1741-4326/abb2d6

Cited by 7 publications

(4 citation statements)

References 54 publications

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“…For instance, edge electrostatic turbulence related to MHD relaxation events has been observed in a reversed field pinch plasma [33]. Similar nonlinear interactions between MHD modes and turbulences during ELMs are reported in KSTAR [34]. Moreover, the correlation between MHD modes and blobs is observed in NSTX (although without relaxation events) [35].…”

Section: Discussionsupporting

confidence: 65%

Observation of MHD-correlated blobs during internal reconnection events in VEST

Jung¹,

Na²,

Kim³

et al. 2022

Nucl. Fusion

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Internal reconnection events (IREs), one of the relaxation events driven by internal magnetohydrodynamic (MHD) instabilities in fusion plasmas, are accompanied by a strongly MHD-correlated blob at the edge in the VEST spherical tokamak. The MHD-correlated blob plays a significant role in the onset and the strength of IREs. Various techniques analyzing visible camera images show correlated waveforms between blobs and magnetic fluctuations, and they produce visualized images of corotating structures of the MHD modes and the MHD-correlated blobs. In the images, a phase drag in the rotations of the two structures initially appears and vanishes on the verge of IREs. IREs maintaining the phase drag, however, leads to a less violent impact in terms of current decrease and magnetic field bursting. In addition, the MHD-correlated blobs are followed by the increasing degree of nonlinear interactions between the internal MHD mode and high-frequency broadband fluctuations (> 60 kHz) at the edge. These results suggest that boundary plasmas can impact internally driven relaxation events via MHD-correlated edge phenomena.

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Section: Discussionsupporting

confidence: 65%

Observation of MHD-correlated blobs during internal reconnection events in VEST

Jung¹,

Na²,

Kim³

et al. 2022

Nucl. Fusion

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“…• Given that the modes co-exist in narrow pedestal, is there condition by which the modes will non-linearly interact [86]? What is the role played by these modes in the triggering mechanism of ELMs [47,87,88]? What is the role played by MHD-like modes in the pedestal and do they compete micro-turbulence?…”

Section: The Challenge To Extrapolate To Lowρ *mentioning

confidence: 99%

Review: Turbulence dynamics during the pedestal evolution between edge localized modes in magnetic fusion devices

Diallo

Laggner

2020

Plasma Phys. Control. Fusion

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Fusion performance has been shown to be related to the H-mode pedestal structure. The pedestal is associated with steep gradients that are the source of free energy for microinstabilities. A variety of instabilities have been shown to co-exist in the pedestal. This paper reviews the experimentally observed signatures of instabilities during the pedestal parameters’ evolutions, with a focus on turbulence observations, made in between edge localized modes (ELMs), in multiple tokamaks. ELMs are cyclic events associated with bursty relaxations of the pedestal. The multiple machine results point to very similar pedestal localized modes suggesting the existence of a unifying mechanism governing the modes’ onset and dynamics. Modeling efforts to identify the generation mechanism of these instabilities are introduced. Several remaining challenges include the study of the instability saturation mechanisms and impact on the pedestal structure formation. Potential future research avenues will require multiscale-non-linear-gyrokinetic analyses to study the non-linear interaction between these instabilities, and which pedestal conditions facilitate such non-linear interactions, as well as the relationship with the formation of the pedestal through transport.

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“…Density fluctuations ( ) for the bispectral analysis are measured with beam emission spectroscopy (BES) in KSTAR. The bispectral analysis of the conditionally ensemble-averaged BES signal is commonly used to show the three-wave non-linear interactions, as studied in KSTAR 60 . Here, squared bicoherence of is defined by where the angle brackets denote ensemble averaging during the analysis period.…”

Section: Methodsmentioning

confidence: 99%

Tailoring tokamak error fields to control plasma instabilities and transport

Yang,

Park,

Jeon

et al. 2024

Nat Commun

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A tokamak relies on the axisymmetric magnetic fields to confine fusion plasmas and aims to deliver sustainable and clean energy. However, misalignments arise inevitably in the tokamak construction, leading to small asymmetries in the magnetic field known as error fields (EFs). The EFs have been a major concern in the tokamak approaches because small EFs, even less than 0.1%, can drive a plasma disruption. Meanwhile, the EFs in the tokamak can be favorably used for controlling plasma instabilities, such as edge-localized modes (ELMs). Here we show an optimization that tailors the EFs to maintain an edge 3D response for ELM control with a minimized core 3D response to avoid plasma disruption and unnecessary confinement degradation. We design and demonstrate such an edge-localized 3D response in the KSTAR facility, benefiting from its unique flexibility to change many degrees of freedom in the 3D coil space for the various fusion plasma regimes. This favorable control of the tokamak EF represents a notable advance for designing intrinsically 3D tokamaks to optimize stability and confinement for next-step fusion reactors.

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Nonlinear energy transfer from low frequency electromagnetic fluctuations to broadband turbulence during edge localized mode crashes

Cited by 7 publications

References 54 publications

Observation of MHD-correlated blobs during internal reconnection events in VEST

Observation of MHD-correlated blobs during internal reconnection events in VEST

Review: Turbulence dynamics during the pedestal evolution between edge localized modes in magnetic fusion devices

Tailoring tokamak error fields to control plasma instabilities and transport

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