Synergy of Turbulent Momentum Drive and Magnetic Braking

Varennes, R; Garbet, X.; Vermare, Laure; Sarazin, Y.; Dif‐Pradalier, G.; Grandgirard, V.; Ghendrih, Ph.; Donnel, Peter; Peret, M; Obrejan, Kevin; Bourne, E

doi:10.1103/physrevlett.128.255002

Cited by 5 publications

(4 citation statements)

References 54 publications

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“…where χ ϕ , V P , and Π res represent diffusivity, pinch velocity, and nondiffusive residual stress, respectively. Previous simulations with adiabatic electron show that the momentum pinch is negligible in comparison to the residual stress [16,39,49,50]. In this study, we neglect the momentum pinch in transport analyses.…”

Section: Role Of Intrinsic Torque In Itb Formationmentioning

confidence: 98%

Global flux-driven gyrofluid simulations of internal transport barrier formation by external torque in weak magnetic shear configuration

Ko,

Kim,

Jhang

et al. 2024

Nucl. Fusion

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Using a global gyrofluid code, we conduct comprehensive flux-driven simulations incorporating external heat and momentum sources/sinks. They involve an external torque ramp keeping a heating power constant. Simulations show the formation of internal transport barriers (ITBs) in ion heat and parallel momentum in weak magnetic shear configuration. The ITB formation is attributed to the reduction of turbulent transport accompanied by strong E × B flow shear generation, where the majority of E × B shear arises from plasma rotation shear. In contrast, only a minor confinement improvement is observed in strong magnetic shear configuration. There exists a substantial difference in the rotation shear between the weak and strong magnetic shear cases at the same amount of external torque. Transport analysis implies that the difference comes from intrinsic rotation generated by residual stress. Global linear simulations demonstrate that the effect of E×B shear on k∥ symmetry breaking is enhanced in weak magnetic shear configuration, explaining the origin of the difference in intrinsic rotation. The ITB is not achieved when the external torque is injected in counter-direction to intrinsic rotation. It is also shown that threshold torque for the ITB formation depends on power and the ratio of external torque to heating power should exceed a critical value to attain an ITB.

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Section: Role Of Intrinsic Torque In Itb Formationmentioning

confidence: 98%

Global flux-driven gyrofluid simulations of internal transport barrier formation by external torque in weak magnetic shear configuration

Ko,

Kim,

Jhang

et al. 2024

Nucl. Fusion

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“…On the other hand, there is the contribution of the toroidal velocity V T . While in experiments one could expect that V T results from a competition between neoclassical processes and turbulence [30], here the presented simulations are performed in an axisymmetric magnetic configurationwhere E r and V T are degenerate if only neoclassical effects are considered-so only the turbulence contributes. Even if the associated contribution to V E is mild in simulations, interestingly the toroidal velocity appears to have a nonmonotonic trend with the safety factor.…”

Section: Reduced Model For Equilibrium E × B Velocitymentioning

confidence: 99%

Safety factor influence on the edge E × B velocity establishment in tokamak plasmas

Varennes,

Vermare,

Garbet

et al. 2023

Plasma Phys. Control. Fusion

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This study is motivated by experiments on Tore Supra and WEST tokamaks where a deepening of the E × B velocity—governed by the radial electric field Er —near the edge is observed when the safety factor decreases in L-mode plasmas. Flux-driven global simulations of ion temperature gradient turbulence recover qualitatively the trend observed in the experiments, i.e. the E × B velocity increases when decreasing the safety factor. From these simulations, multiple clues point out the role of turbulence in the establishment of the radial electric field even though the turbulent intensity increases with the safety factor. The proposed mechanism to elucidate this phenomenon, backed up by a reduced model, is that the damping of the poloidal flow, governed by the neoclassical friction, increases more strongly with the safety factor than the turbulent drive for Er , due to the ( r , θ ) component of the Reynolds stress.

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“…In the other half of this feedback loop, micro-turbulence can in turn slow down the growth of the large-scale cell via the turbulent viscosity and electrostatic scattering. In addition, stochastic magnetic fields can produce a magnetic braking effect [77], which enhances the plasma inertia and opposes the mode growth. This effect may be thoughts of a stochastic analogue of the nonlinear force identified by Rutherford [78].…”

Section: Effects Of Stochastic Magnetic Fields On Turbulencementioning

confidence: 99%

Theory of mean E × B shear in a stochastic magnetic field: ambipolarity breaking and radial current

Guo

Jiang²,

Diamond³

et al. 2022

Plasma Phys. Control. Fusion

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The mean E×B shear in a stochastic magnetic field is calculated, using the radial force balance relation and transport equations. This analysis is relevant to the L→H transition with resonant magnetic perturbations (RMP), and special focus is placed upon the physics of non-ambipolar transport and radial current. The key physical process is the flow of fluctuating current along wandering magnetic fields. The increments in poloidal and toroidal rotation, density and ion pressure are calculated. The radial envelope of the magnetic perturbations inside the plasma defines a new scale l_env, which is the characteristic scale of the magnetic fluctuation intensity profile. The net particle outflow due to stochastic magnetic fields is calculated and is determined by the net radial current through the separatrix. Implications for the L→H transition are discussed.

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Synergy of Turbulent Momentum Drive and Magnetic Braking

Cited by 5 publications

References 54 publications

Global flux-driven gyrofluid simulations of internal transport barrier formation by external torque in weak magnetic shear configuration

Global flux-driven gyrofluid simulations of internal transport barrier formation by external torque in weak magnetic shear configuration

Safety factor influence on the edge E × B velocity establishment in tokamak plasmas

Theory of mean E × B shear in a stochastic magnetic field: ambipolarity breaking and radial current

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