3D field phase-space control in tokamak plasmas

Park, Jong‐Kyu; Jeon, Y.M.; In, Y.; Ahn, J.-W.; Nazikian, R.; Park, Gunyoung; Kim, Jae Hyun; Lee, Hyung Ho; Ko, W. H.; Kim, Hyun‐Seok; Logan, N. C.; Wang, Zhirui; Feibush, Eliot; Ménard, J.; Zarnstroff, Michael C.

doi:10.1038/s41567-018-0268-8

Cited by 96 publications

(129 citation statements)

References 49 publications

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“…In parallel, dedicated RMP spectral optimization studies have converged on the crucial role of maximizing resonant coupling to the edge rational surfaces [21,7,22], and if conditions require it, maximizing edge resonant coupling while holding core resonant coupling to a sufficiently low value to avoid penetration of the core resonant surfaces [10,23,24]. Though the reason ∆ up was so effective in AUG is not yet resolved, an increase in edge resonant coupling may partially explain this result.…”

Section: Introductionmentioning

confidence: 99%

The effect of plasma shape and neutral beam mix on the rotation threshold for RMP-ELM suppression

et al. 2019

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Varying the neutral beam injection (NBI) mix reveals a clear pedestal-top rotation threshold for edge localized mode (ELM) suppression by resonant magnetic perturbations. Guided by expectations for the RMP penetration mechanism, the rotation threshold is found to correspond to a critical radius for the ExB rotation zero-crossing. No such critical radius is observed for the electron perpendicular rotation zero-crossing. Varying the amount and ratio of power in different NBI source geometries (termed the NBI mix) also reveals that the rotation threshold can be crossed at widely varying total injected NBI torques. Computing the local torque density at the edge, the rotation threshold is found to be crossed when the local edge NBI torque is negative in nearly all discharges. Reducing the upper triangularity from the ITERsimilar value of 0.3 to 0.1 significantly reduces the pedestal height and width. This in turn: 1) Increases the rotation threshold and yields a more outward critical ExB rotation zero-crossing location. 2) Decreases the density threshold, consistent with a comparable collisionality range at lower pedestal temperatures. 3) Increases the input torque requirement, due to observed lower confinement and smaller intrinsic torque. These findings represent an important step along the road to predicting ELM suppression access conditions in future tokamaks such as ITER, where the toroidal rotation is expected to be low and consequently the rotation zero-crossing far from the pedestal-top.

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Section: Introductionmentioning

confidence: 99%

The effect of plasma shape and neutral beam mix on the rotation threshold for RMP-ELM suppression

et al. 2019

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“…1 This method was first demonstrated in DIII-D 2 and thereafter observed on several tokamaks worldwide. [3][4][5][6][7][8][9] Various models have been proposed to explain the causes of ELM suppression, [10][11][12][13] however important characteristics of ELM suppression remain unexplained. One characteristic of ELM suppression in DIII-D low collisionality (ν * e <0.5) ITER-similar-shape (ISS) plasmas is the low pedestal density n e,ped ≈ 2-3×10 19 m -3 required for access to ELM suppression.…”

mentioning

confidence: 99%

Multi-diagnostic analysis of plasma filaments in the island divertor

Zoletnik

Anda

Biedermann

et al. 2019

Plasma Phys. Control. Fusion

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Filaments or blobs are well known structures in turbulence in magnetic fusion devices, they are considered to be the major cross-transport channel in the scrape off layer. They originate at the last closed magnetic flux surface and propagate out on the low field side of toroidal devices due to polarization in the curved magnetic field. The Wendelstein 7-X stellarator has a complex three-dimensional magnetic field structure and additionally the plasma is bounded by a chain of magnetic islands, forming an island divertor. After the first observation of filaments in Wendelstein 7-X with video cameras a multi-diagnostic study is presented in this paper to reveal their 3D structure and dynamics. Filaments are seen to be born at the edge and, at least in some cases, seen to extend to up to 4 toroidal turns. After moving radially out a few cm they enter the edge island. Here they disappear from the equatorial plane and about 200 microseconds later reappear on the outboard side of the island. A long-wavelength (∼20–30 cm) quasi coherent mode is observed in both regions where filaments appear. The similarities and differences between the filaments seen in W7-X and other devices are discussed. Possible explanations for this strange radial propagation are considered, together with the likely role of filaments in the edge and island density profile.

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“…However, the operation window of the 'ELM' suppressed regime is quite limited and efforts to expand the operating window have been largely empirical. Recently a successful suppression experiment with a pre-designed polar diagram, calculated with IPEC code including the plasma response model, spanned by the amplitude and phase of RMP coils has been conducted [122]. Here, one can select the amplitude and phase of RMP coils to operate in the region where suppression of the 'ELM' is expected for given RMP coil configurations for a specific helicity and set of physical parameters.…”

Section: What Are the New Findings In The Study Of Alfvén Mode Instabmentioning

confidence: 99%

Newly uncovered physics of MHD instabilities using 2-D electron cyclotron emission imaging system in toroidal plasmas

Park

2019

Advances in Physics: X

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Validation of physics models using the newly uncovered physics with a 2-D electron cyclotron emission imaging (ECEi) system for magnetic fusion plasmas has either enhanced the confidence or substantially improved the modeling capability. The discarded "full reconnection model" in sawtooth instability is vindicated and established that symmetry and magnetic shear of the 1/1 kink mode are critical parameters in sawtooth instability. For the 2/ 1 instability, it is demonstrated that the 2-D data can determine critical physics parameters with a high confidence and the measured anisotropic distribution of the turbulence and its flow in presence of the 2/1 island is validated by the modelled potential and gyro-kinetic calculation. The validation process of the measured reversed-shear Alfvéneigenmode (RSAE) structures has improved deficiencies of prior models. The 2-D images of internal structure of the ELMs and turbulence induced by the resonant magnetic perturbation (RMP) have provided an opportunity to establish firm physics basis of the ELM instability and role of RMPs. The importance of symmetry in determining the reconnection time scale and role of magnetic shear of the 1/1 kink mode in sawtooth instability may be relevant to the underlying physics of the violent kink instability of the filament ropes in a solar flare.

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3D field phase-space control in tokamak plasmas

Cited by 96 publications

References 49 publications

The effect of plasma shape and neutral beam mix on the rotation threshold for RMP-ELM suppression

The effect of plasma shape and neutral beam mix on the rotation threshold for RMP-ELM suppression

Multi-diagnostic analysis of plasma filaments in the island divertor

Newly uncovered physics of MHD instabilities using 2-D electron cyclotron emission imaging system in toroidal plasmas

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