Quiescent double barrier high-confinement mode plasmas in the DIII-D tokamak

Burrell, K.H.; Austin, M. E.; Brennan, D. P.; DeBoo, J. C.; Doyle, E. J.; Fenzi, C.; Fuchs, C.; Gohil, P.; Greenfield, C. M.; Groebner, R. J.; Lao, L. L.; Luce, T.C.; Makowski, M. A.; McKee, G. R.; Moyer, R. A.; Petty, C. C.; Porkoláb, M.; Rettig, C. L.; Rhodes, T. L.; Rost, J. C.; Stallard, B. W.; Strait, E. J.; Synakowski, E. J.; Wade, M. R.; Watkins, J. G.; West, W. P.

doi:10.1063/1.1355981

Cited by 195 publications

(242 citation statements)

References 21 publications

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“…They originate in part from time varying plasma currents driven by magnetohydrodynamical (MHD) modes [1] and tearing instabilities on rational flux surfaces [2], thermoelectric currents flowing on open field lines [3], coherent modes [4], edge harmonic oscillations [5] and edge localized modes (ELMs) [6] as well as an array of higher frequency electromagnetic waves and turbulence [7]. Outside the plasma, sources such as field-errors from asymmetries in toroidal and poloidal magnetic field coils, magnetic materials, vacuum vessel image and return currents [8], external control coils used to stabilize plasma modes, and correction coils [9] used to minimize perturbations from known field-errors on low integer rational surfaces all contribute to the structure of the magnetic field in which the plasma resides.…”

Section: Introductionmentioning

confidence: 99%

The physics of edge resonant magnetic perturbations in hot tokamak plasmas

et al. 2006

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Small edge resonant magnetic perturbations are used to control the pedestal transport and stability in low electron collisionality ( e * ), ITER relevant, poloidally diverted plasmas. The applied perturbations reduce the height of the density pedestal and increase its width while increasing the height of the electron pedestal temperature and its gradient.The effect of the perturbations on the pedestal gradients is controlled by the current in the perturbation coil, the poloidal mode spectrum of the coil, the neutral beam heating power and the divertor deuterium fueling rate. Large pedestal instabilities, referred to as edge as an array of higher frequency electromagnetic waves and turbulence [7]. Outside the plasma, sources such as field-errors from asymmetries in toroidal and poloidal magnetic field coils, magnetic materials, vacuum vessel image and return currents [8], external control coils used to stabilize plasma modes, and correction coils [9] used to minimize perturbations from known field-errors on low integer rational surfaces all contribute to the structure of the magnetic field in which the plasma resides. At the edge of the plasma where the safety factor [ q ( ) defined as the rate of change in toroidal magnetic flux with poloidal magnetic flux ] increases rapidly, all of these perturbations contribute to the creation of closely spaced resonant magnetic islands which may result in the formation of edge stochastic layers. In a poloidally diverted tokamak, the high magnetic shear q across the edge of the plasma results in an increased density of island states and a significantly higher probability of forming open stochastic layers that connect magnetic field lines to plasma facing material surfaces [10]. Thus, the edge plasma is immersed in a dynamically complex magnetic topology over the same region where substantial radial flows of mass and energy, driven by large gradients, compete with strong turbulent transport in highly sheared toroidal and poloidal plasma flow fields. Large radial gradients in the plasma pressure are often established by a strong reduction in turbulent 4 transport due to sheared plasma flow. The large edge gradients are a key factor in the establishment of good confinement levels that make the tokamak the leading candidate for fusion reactors. However, they also lead to the instabilities known as ELMs which drive impulsive energy losses that can be detrimental to plasma facing surfaces. It is easy to understand why the development of tools to control the pedestal transport and stability is a compelling issue for improving the performance and operational safety of high energy density tokamak based fusion confinement systems.A strong motivation for understanding the physics of edge stochastic layers is to enable the development of predictable and reliable tools for controlling key fusion plasma pedestal processes such as: the plasma temperature and pressure at the top of the pedestal, the size and frequency of ELMs, the energy and particle exhaust rate in steady-state cond...

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Section: Introductionmentioning

confidence: 99%

The physics of edge resonant magnetic perturbations in hot tokamak plasmas

et al. 2006

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“…32͒ and DIII-D, 33 and ELM-free operation in the QH-mode. [34][35][36][37][38][39] Pioneering work on the effect of edge stochastic fields in circular limited plasmas was done by the TEXT group, [40][41][42][43] by the Tore-Supra group ͑Refs. 44 and 45, and references therein͒, and by the TEXTOR group.…”

Section: Introductionmentioning

confidence: 99%

Effect of island overlap on edge localized mode suppression by resonant magnetic perturbations in DIII-D

Fenstermacher¹,

Evans²,

Osborne³

et al. 2008

Physics of Plasmas

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Recent DIII-D [J. L. Luxon et al., Nucl. Fusion 43, 1813 (2003)] experiments show a correlation between the extent of overlap of magnetic islands induced in the edge plasma by perturbation coils and complete suppression of Type-I edge localized modes (ELMs) in plasmas with ITER-like electron pedestal collisionality νe*∼0.1, flux surface shape and low edge safety factor (q95≈3.6). With fixed amplitude n=3 resonant magnetic perturbation (RMP), ELM suppression is obtained only in a finite window in the edge safety factor (q95) consistent with maximizing the resonant component of the applied helical field. ELM suppression is obtained over an increasing range of q95 by either increasing the n=3 RMP strength, or by adding n=1 perturbations to “fill in” gaps between islands across the edge plasma. The suppression of Type-I ELMs correlates with a minimum width of the edge region having magnetic islands with Chirikov parameter >1.0, based on vacuum calculations of RMP mode components excluding the plasma response or rotational shielding. The fraction of vacuum magnetic field lines that are lost from the plasma, with connection length to the divertor targets comparable to an electron-ion collisional mean free path, increases throughout the island overlap region in the ELM suppressed case compared with the ELMing case.

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“…In experiments, much effort has been devoted to reducing the size of ELMs to an acceptable level [7][8][9]. In contrast to the large crash of the pressure profile in the ELMy H mode, the edge pressure profile finds a steady weak oscillatory state in the QH mode, so impurities are expelled effectively and the plasma facing components are not eroded [10]. Thus, the QH mode is an attractive scenario for a fusion reactor.…”

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From Phase Locking to Phase Slips: A Mechanism for a QuiescentHmode

Guo

Diamond

2015

Phys. Rev. Lett.

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We demonstrate that E × B shear, V 0 E×B , governs the dynamics of the cross phase of the peelingballooning-(PB-)mode-driven heat flux, and so determines the evolution from the edge-localized (ELMy) H mode to the quiescent (Q) H mode. A physics-based scaling of the critical E × B shearing rate (V 0 E×B;cr ) for accessing the QH mode is predicted. The ELMy H mode to the QH-mode evolution is shown to follow from the conversion from a phase locked state to a phase slip state. In the phase locked state, PB modes are pumped continuously, so bursts occur. In the slip state, the PB activity is a coherent oscillation. Stronger E × B shearing implies a higher phase slip frequency. This finding predicts a new state of cross phase dynamics and shows a new way to understand the physics mechanism for ELMy to the QH-mode evolution.

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Quiescent double barrier high-confinement mode plasmas in the DIII-D tokamak

Cited by 195 publications

References 21 publications

The physics of edge resonant magnetic perturbations in hot tokamak plasmas

The physics of edge resonant magnetic perturbations in hot tokamak plasmas

Effect of island overlap on edge localized mode suppression by resonant magnetic perturbations in DIII-D

From Phase Locking to Phase Slips: A Mechanism for a QuiescentHmode

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