Pedestal Bifurcation and Resonant Field Penetration at the Threshold of Edge-Localized Mode Suppression in the DIII-D Tokamak

Nazikian, R.; Paz-Soldan, C.; Callen, J. D.; deGrassie, J.S.; Eldon, D.; Evans, T.E.; Ferraro, N.M.; Grierson, B. A.; Groebner, R. J.; Haskey, S. R.; Hegna, C. C.; King, J. D.; Logan, N. C.; McKee, G. R.; Moyer, R. A.; Okabayashi, M.; Orlov, D. M.; Osborne, T.H.; Park, Jong‐Kyu; Rhodes, T. L.; Shafer, Morgan; Snyder, P. B.; Solomon, W. M.; Strait, E. J.; Wade, M. R.

doi:10.1103/physrevlett.114.105002

Cited by 152 publications

(219 citation statements)

References 27 publications

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“…This may also explain a similar discrepancy between the measured response and MARS-F modeling found in DIII-D recently [24]. Different from the observation of field penetration on ELM suppression in DIII-D [17], the penetrated toroidal mode number here is the same as the applied one.…”

contrasting

confidence: 50%

“…This is the first observation of full ELM suppression using RMPs in the medium plasma collisionality regime in EAST, and it expands beyond the previous observations of ELM suppression on DIII-D [1,3] and KSTAR [7]. It is found that not only the formation of a magnetic island near the edge [17] but also a critical level of magnetic topological change, taking into account plasma response, play a key role in accessing final ELM suppression. This observation also reveals different roles of linear and nonlinear response effects on ELM suppression.…”

supporting

confidence: 49%

“…Nonlinear plasma response has been observed in the JET totamak [15]. The possible formation of a magnetic island near the plasma edge [16] with a toroidal Fourier mode number n ¼ 1 during ELM suppression by using n ¼ 2 RMP has been recently observed on DIII-D [17]. However, the key difference between ELM suppression and mitigation and the different roles of linear and nonlinear plasma response on ELM suppression are still not clear.…”

mentioning

confidence: 98%

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Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak

et al. 2016

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Evidence of a nonlinear transition from mitigation to suppression of the edge localized mode (ELM) by using resonant magnetic perturbations (RMPs) in the EAST tokamak is presented. This is the first demonstration of ELM suppression with RMPs in slowly rotating plasmas with dominant radio-frequency wave heating. Changes of edge magnetic topology after the transition are indicated by a gradual phase shift in the plasma response field from a linear magneto hydro dynamics modeling result to a vacuum one and a sudden increase of three-dimensional particle flux to the divertor. The transition threshold depends on the spectrum of RMPs and plasma rotation as well as perturbation amplitude. This means that edge topological changes resulting from nonlinear plasma response plays a key role in the suppression of ELM with RMPs. DOI: 10.1103/PhysRevLett.117.115001 Magnetic reconnection and the resultant topological change play an important role in plasma dynamics in both laboratory and space plasma physics research. The formation of an edge stochastic magnetic field caused by resonant magnetic perturbations (RMPs) is believed to be the reason for the suppression of periodic crash events near the plasma edge known as the edge localized mode (ELM) observed in the DIII-D tokamak [1]. The ELM causes transient heat loads to the plasma facing components and may degrade them on the next generation fusion device like ITER [2]. The reduction of free energy in the edge pressure gradient and current because of field stochasticity moves the plasma into a stable regime against the ELM [3]. This successful experiment motivated ELM control using RMPs in many other tokamaks [4][5][6][7]. However, the plasma response effect usually shields the external applied RMPs and may significantly reduce the magnetic field stochasticity [8][9][10][11], which makes this mechanism questionable. Different from topological change, the linear peelinglike magneto hydro dynamics (MHD) response has been found to play an important role in ELM control [12][13][14]. Nonlinear plasma response has been observed in the JET totamak [15]. The possible formation of a magnetic island near the plasma edge [16] with a toroidal Fourier mode number n ¼ 1 during ELM suppression by using n ¼ 2 RMP has been recently observed on DIII-D [17]. However, the key difference between ELM suppression and mitigation and the different roles of linear and nonlinear plasma response on ELM suppression are still not clear.In this Letter, we report the first observation of full ELM suppression using low n RMPs in slowly rotating plasmas with dominant radio-frequency (rf) wave heating, which is potentially important for the application of this method for a future fusion device. This is the first observation of full ELM suppression using RMPs in the medium plasma collisionality regime in EAST, and it expands beyond the previous observations of ELM suppression on DIII-D [1,3] and KSTAR [7]. It is found that not only the formation of a magnetic island near the edge [17] but also a critical leve...

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supporting

confidence: 49%

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confidence: 98%

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Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak

et al. 2016

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“…At the same time, the absence of H α spikes at those burst events indicates that the bursts are localized in the plasma edge region, which is distinguished from the usual ELM crashes involving the collapse of the pedestal with large particle transport. The pattern velocity of the ELMs in the crash-suppression phase is typically small on the order of ∼1 km=s and sometimes they appear to halt, similar to the reduction of perpendicular electron flow in the ELM-crash-suppression phase observed in DIII-D [15]. On the other hand, the pattern velocity of ordinary ELMs in the KSTAR device is observed in a wide range (up to several 10s km=s) in both electron and ion diamagnetic directions.…”

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confidence: 57%

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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“…Significant E r profile change at the plasma edge usually accompanies the application of RMPs [20][21][22][23][24][25][26]. Our results suggest that the E × B flow shear may influence ELMs through its influence on the kink/peeling instabilities.…”

Section: E × B Flow Shear Drive Of the Linear Low-n Modes Of Eho In Tmentioning

confidence: 72%

E × Bflow shear drive of the linear low-nmodes of EHO in the QH-mode regime

Wan

Wang

et al. 2017

Nucl. Fusion

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A new model for the edge harmonic oscillations (EHOs) in the quiescent H-mode regime has been developed, which successfully reproduces the recent observations in the DIII-D tokamak. In particular, at high E × B flow shear only a few low-n kink modes remain unstable at the plasma edge, consistent with the EHO behavior, while at low E × B flow shear, the unstable mode spectrum is significantly broadened, consistent with the low-n broadband electromagnetic turbulence behavior. The model is based on a new mechanism for destabilizing low-n kink/peeling modes by the E × B flow shear, which underlies the EHOs, separately from the previously found Kelvin-Helmholtz drive. We find that the differential advection of mode vorticity by sheared E × B flows modifies the 2D pattern of mode electrostatic potential perpendicular to the magnetic field lines, which in turn causes a radial expansion of the mode structure, an increase of field line bending away from the mode rational surface, and a reduction of inertial stabilization. This enhances the kink drive as the parallel wavenumber increases significantly away from the rational surface at the plasma edge where the magnetic shear is also strong. This destabilization is also shown to be independent of the sign of the flow shear, as observed experimentally, and has not been taken into account in previous pedestal linear stability analyses. Verification of the veracity of this EHO mechanism will require analysis of the nonlinear evolution of low-n kink/peeling modes so destabilized in the linear regime.

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Pedestal Bifurcation and Resonant Field Penetration at the Threshold of Edge-Localized Mode Suppression in the DIII-D Tokamak

Cited by 152 publications

References 27 publications

Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak

Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak

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

E × Bflow shear drive of the linear low-nmodes of EHO in the QH-mode regime

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