Effect of resonant magnetic perturbations on microturbulence in DIII-D pedestal

Holod, I.; Zhang, Lin; Nazikian, R.; Spong, D. A.; Wingen, A.

doi:10.1088/0029-5515/57/1/016005

Cited by 32 publications

(43 citation statements)

References 22 publications

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“…We should note that the TM1 code does not include the non-resonant plasma kink response. While there has been consideration that the kink response can drive pump-out 37 and excite ballooning modes, 38,39 recent global gyro-kinetic simulations with the GTC 40 and XGC 41 codes do not show significant contribution of the kink response on finite-n ballooning stability and neoclassical cross-field transport for the low-collisionality plasmas studied in this Letter. This leaves the tearing response for which TM1 is well suited for performing analysis at ITER relevant resistivity and collisionality.…”

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confidence: 83%

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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confidence: 83%

Multi-diagnostic analysis of plasma filaments in the island divertor

Zoletnik

Anda

Biedermann

et al. 2019

Plasma Phys. Control. Fusion

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mentioning

confidence: 84%

The density dependence of edge-localized-mode suppression and pump-out by resonant magnetic perturbations in the DIII-D tokamak

Nazikian

Grierson

et al. 2019

Physics of Plasmas

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The density dependence of edge-localized-mode (ELM) suppression and density pump-out (density reduction) by n = 2 resonant magnetic perturbations (RMPs) is consistent with the effects of narrow well-separated magnetic islands at the top and bottom of the H-mode pedestal in DIII-D low-collisionality plasmas. Nonlinear two-fluid MHD simulations for DIII-D ITER Similar Shape (ISS) discharges show that, at low collisionality (ν * e <0.5), low pedestal density is required for resonant field penetration at the pedestal top (n e,ped ≈ 2.5×10 19 m -3 at ψ N ≈0.93), consistent with the ubiquitous low density requirement for ELM suppression in these DIII-D plasmas. The simulations predict a drop in the pedestal pressure due to parallel transport across these narrow width (Δψ N ≈0.02) magnetic islands at the top of the pedestal that is stabilizing to Peeling-Ballooning-Modes (PBMs), and comparable to the pedestal pressure reduction observed in experiment at the onset of ELM suppression. The simulations predict density pump-out at experimentally relevant levels (Δn e /n e ≈-20%) at low pedestal collisionality (ν * e ≈0.1) due to very narrow (Δψ N ≈0.01-0.02) RMP driven magnetic islands at the pedestal foot at ψ N ≈0.99. The simulations show decreasing pump-out with increasing density, consistent with experiment, resulting from the inverse dependence of parallel particle transport on collisionality at the foot of the pedestal. The robust screening of resonant fields is predicted between the top and bottom of the pedestal during density pump-out and ELM suppression, consistent with the preservation of strong temperature gradients in the edge transport barrier as seen in experiment.

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“…When spacing between adjacent rational surfaces is not large (as with high n RMPs or high q 95 operation) it is important to understand why penetration at one rational surface may be sufficient, but a nearby rational surface is not. Answering this question will require further coupling of microscale fluctuation models with global transport models [56,20] to understand this critical spacing.…”

Section: Extrapolation Of the Rotation Thresholdmentioning

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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Effect of resonant magnetic perturbations on microturbulence in DIII-D pedestal

Cited by 32 publications

References 22 publications

Multi-diagnostic analysis of plasma filaments in the island divertor

Multi-diagnostic analysis of plasma filaments in the island divertor

The density dependence of edge-localized-mode suppression and pump-out by resonant magnetic perturbations in the DIII-D tokamak

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

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