Effect of strong radial variation of the ion diamagnetic frequency on internal ballooning modes

Hastie, R. J.; Catto, Peter J.; Ramos, J. J.

doi:10.1063/1.1310201

Cited by 43 publications

(49 citation statements)

References 16 publications

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“…Due to diamagnetic effects in the pedestal region 15,42 , modes with high toroidal mode numbers are expected to be stabilized. The maximum unstable n is estimated by n max ∼ = ( L p ) / (qρ i ) assuming the diamagnetic drift frequency (ω * pi ) to be unchanged throughout the pedestal.…”

Section: Identification Of the Pedestal Pressure Gradient Limit Bmentioning

confidence: 99%

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

Pitzschke

Behn

Sauter

et al. 2011

Plasma Phys. Control. Fusion

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The dynamics of electron temperature and density profiles during quasi-stationary H-mode phases in the TCV tokamak has been investigated for type III and type I ELMs using electron cyclotron heating (ECH) to vary the collisionality. At heating power levels close to the threshold for the L-H transition, ELMs of type III were observed, with an energy loss per ELM below 10% of the total plasma energy. Electron temperature and pressure showed no significant increase during the phase before the ELM crash. ELMs of type I were characterized by a lower repetition rate, but caused fractional energy losses reaching 20%. For this ELM type, a clear increase in pedestal pressure and pressure gradient was observed before the collapse associated with the ELM event. The rapid drop in electron temperature also affected the plasma core explaining the rather large energy losses per ELM. Ideal MHD stability calculations of the edge pedestal with the KINX code showed that high-n ballooning modes restricted the achievable pressure gradient at high collisionality and ELMs of type III. With additional heating and type I ELMs, stability limits were set by medium-n kink-ballooning modes. Comparing the values of the pressure gradients and current densities obtained from experimental data with those of ideal MHD stability calculations showed good agreement. The model, however, needs to account for the radial displacement of the location of maximum pressure gradient during the ELM cycle.

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Section: Identification Of the Pedestal Pressure Gradient Limit Bmentioning

confidence: 99%

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

Pitzschke

Behn

Sauter

et al. 2011

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

show abstract

“…The discussion is based on the earlier research about diamagnetic stabilization effects on the ballooning modes in Ref. 10. When the bootstrap current effects on the equilibrium are taken into account, however, the infernal mode appears and its behavior deviates from that of ballooning modes.…”

Section: Numerical Resultsmentioning

confidence: 99%

“…The current investigation may be regarded as an extension of existing researches for diamagnetic stabilization. 10,12 So far in this field the fully kinetic treatment of pedestal physics is still limited to using the fixed boundary ballooning mode formalism. Most of peeling ballooning 9 mode calculations are still based on the ideal MHD framework.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…12. Based on the ballooning mode investigation, 10 Reference 12 concludes that, when there is a radial variation in the diamagnetic frequency ω * i , the diamagnetic stabilization is less effective. Instead, we find that, when the bootstrap current effect on the equilibrium is taken into account, the diamagnetic stabilization can be effective, depending sensitively on the safety factor value at the region where the safety factor is flat or reversed and also on the toroidal rotation direction.…”

Section: Introductionmentioning

confidence: 99%

“…Besides, we point out that the current investigation is based on the two dimensional free boundary AEGIS (Adaptive EiGenfunction Independent Solutions) code, 13 while the previous conclusion about the ineffectiveness of the diamagnetic stabilization is based on the conventional one dimensional ballooning representation. 10,12 As pointed out in Ref. 14 the conventional ballooning mode representation cannot be used at the plasma edge.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Diamagnetic drift effects on the low-n magnetohydrodynamic modes at the high mode pedestal with plasma rotation

Zheng¹,

Kotschenreuther²,

Valanju³

2014

Physics of Plasmas

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The diamagnetic drift effects on the low-n magnetohydrodynamic instabilities at the high-mode (H-mode) pedestal are investigated in this paper with the inclusion of bootstrap current for equilibrium and rotation effects for stability, where n is the toroidal mode number. The AEGIS ( (1983)], with bootstrap current taken into account. Generally speaking, the diamagnetic drift effects are stabilizing. Our results show that the effectiveness of diamagnetic stabilization depends sensitively on the safe factor value (q s ) at the safety-factor reversal or plateau region. The diamagnetic stabilization are weaker, when q s is larger than an integer; while stronger, when q s is smaller or less larger than an integer. We also find that the diamagnetic drift effects also depend sensitively on the rotation direction. The diamagnetic stabilization in the co-rotation case is stronger than in the counter rotation case with respect to the ion diamagnetic drift direction.

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ELMs and the Role of Current-Driven Instabilities in the Pedestal

Snyder

Wilson

2002

Contrib. Plasma Phys.

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Edge localized modes (ELMs) can limit tokamak performance both directly, via large tran‐sient heat loads to divertor plates, and indirectly, through constraints placed on the edge pedestal height which impact global confinement. Understanding the physics of ELMs has proved challenging, in part because the sharp edge pressure gradients and consequent large bootstrap currents in the pedestal provide drive for a variety of magnetohydrodynamic (MHD) instabilities over a wide range of toroidal mode numbers (n). We present a brief review of recent developments in ELM theory, focusing on ELMs whose frequency increases with input power, and emphasizing theories which incorporate current‐driven MHD instabilities such as external kink or “peeling” modes. We describe recent progress both in analytic theory of peeling‐ballooning modes, and in the development of computational tools which can calculate edge MHD growth rates in shaped toroidal geometry over the full relevant spectrum of n. This progress has led to the development and refinement of ELM theories based on peeling‐ballooning modes, including models for ELM characteristics and temperature pedestal limits. Comparisons of ELM theory with experiment, and recent experimental efforts to control ELMs will also be discussed.

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Effect of strong radial variation of the ion diamagnetic frequency on internal ballooning modes

Cited by 43 publications

References 16 publications

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

Diamagnetic drift effects on the low-n magnetohydrodynamic modes at the high mode pedestal with plasma rotation

ELMs and the Role of Current-Driven Instabilities in the Pedestal

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