Experimental evidence of electron-cyclotron current drive-based neoclassical tearing mode suppression threshold reduction during mode locking on DIII-D

Nelson, A.; Logan, N. C.; Choi, W.; Strait, E. J.; Kolemen, Egemen

doi:10.1088/1361-6587/ab9b3b

Cited by 7 publications

(9 citation statements)

References 70 publications

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“…Another concern relates to the loss of H-mode incurred after mode locking, as the locked island couples to modes at other rational surfaces and viscously brakes the background plasma rotation [13,14]. Recent DIII-D experiments suggest loss of H-mode may proceed on a momentum confinement timescale [15], allowing for H-mode to be preserved by quickly stabilising the island after locking, as was experimentally demonstrated for large locked islands in DIII-D [3,16]. Furthermore, small locked islands might not have as deleterious an impact on the background rotation [17], and the small locked NTMs considered here might not lead to loss of H-mode, similarly to the small LMs induced by resonant magnetic perturbations (RMPs) in the context of edge localised mode (ELM) suppression [18].…”

Section: Loss Of H-modementioning

confidence: 99%

On the stabilisation of locked tearing modes in ITER and other large tokamaks

Nies¹,

Reiman²,

Fisch³

2022

Nucl. Fusion

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Tearing modes in tokamaks typically rotate while small and then lock at a fixed location when larger. Research on present-day devices has focused almost exclusively on stabilisation of rotating modes, as it has been considered imperative to avoid locked modes. However, in larger devices, stabilisation during the rotating phase is made difficult by fast locking at small island widths, and large broadening of the stabilising wave-driven current profile. In contrast, the smaller island width at locking not only mitigates the deleterious consequences of locked modes, but also permits their efficient stabilisation. On large devices, it thus becomes surprisingly advantageous to allow the mode to grow and lock naturally before stabilising it, challenging the mainstream strategy of neoclassical tearing mode stabilisation during the rotating phase. Calculations indicate that a locked island stabilisation strategy should be adopted in the ITER tokamak, with a large potential impact on the fusion gain and disruptivity.

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Section: Loss Of H-modementioning

confidence: 99%

On the stabilisation of locked tearing modes in ITER and other large tokamaks

Nies¹,

Reiman²,

Fisch³

2022

Nucl. Fusion

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“…• From the hardware point of view, the 40 ECE probes are installed close to one another and their radial locations can vary significantly in each discharge. Therefore, it is likely that the collected information by these probes overlap both in the spatial and temporal domain [62]. As a result, the missing information in one probe might be covered by the neighboring probes.…”

Section: Impact Of Ece Signal Resolutionmentioning

confidence: 99%

Alfvén eigenmode classification based on ECE diagnostics at DIII-D using deep recurrent neural networks

et al. 2021

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Modern tokamaks have achieved significant fusion production, but further progress towards steady-state operation has been stymied by a host of kinetic and MHD instabilities. Control and identification of these instabilities is often complicated, warranting the application of data-driven methods to complement and improve physical understanding. In particular, Alfvén eigenmodes are a class of ubiquitous mixed kinetic and MHD instabilities that are important to identify and control because they can lead to loss of confinement and potential damage to the walls of a plasma device. In the present work, we use reservoir computing networks (RCNs) to classify Alfvén eigenmodes in a large, expert-identified database of DIII-D discharges, covering a broad range of operational parameter space. Despite the large parameter space, we show excellent classification and prediction performance, with an average hit rate of 91% and false alarm ratio of 7%, indicating promise for future implementation with additional diagnostic data and consolidation into a real-time control strategy.

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“…As for the dynamic RMP, it can be utilized to unlock the magnetic island and maintain a stable toroidal and poloidal rotation [18]. Lately, experimental and numerical results show that the synergetic application of RMP and electron cyclotron current drive (ECCD) is a promising and effective method to control the NTM [19][20][21]. The RMP can be used as an auxiliary method to lock and locate the phase of the NTM, and then to enhance the accuracy and effectiveness of the ECCD.…”

Section: Introductionmentioning

confidence: 99%

Screening of resonant magnetic perturbation penetration by flows in tokamak plasmas based on two-fluid model

Tang¹,

Wang²,

Wei³

et al. 2021

Preprint

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Numerical simulation on the resonant magnetic perturbation penetration is carried out by the newly-updated initial value code MDC (MHD@Dalian Code). Based on a set of two-fluid four-field equations, the bootstrap current, parallel and perpendicular transport effects are included appropriately. Taking into account the bootstrap current, a mode penetration like phenomenon is found, which is essentially different from the classical tearing mode model. It may provide a possible explanation for the finite mode penetration threshold at zero rotation detected in experiments. To reveal the influence of diamagnetic drift flow on the mode penetration process, E × B drift flow and diamagnetic drift flow are separately applied to compare their effects. Numerical results show that, a sufficiently large diamagnetic drift flow can drive a strong stabilizing effect on the neoclassical tearing mode. Furthermore, an oscillation phenomenon of island width is discovered. By analyzing in depth, it is found that, this oscillation phenomenon is due to the negative feedback regulation of pressure on the magnetic island. This physical mechanism is verified again by key parameter scanning.

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Experimental evidence of electron-cyclotron current drive-based neoclassical tearing mode suppression threshold reduction during mode locking on DIII-D

Cited by 7 publications

References 70 publications

On the stabilisation of locked tearing modes in ITER and other large tokamaks

On the stabilisation of locked tearing modes in ITER and other large tokamaks

Alfvén eigenmode classification based on ECE diagnostics at DIII-D using deep recurrent neural networks

Screening of resonant magnetic perturbation penetration by flows in tokamak plasmas based on two-fluid model

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