Dynamic transport regulation by zonal flow-like structures in the TJ-II stellarator

Alonso, A.; Hidalgo, C.; Pedrosa, M. A.; Carralero, D.; Silva, Carlos

doi:10.1088/0029-5515/52/6/063010

Cited by 15 publications

(42 citation statements)

References 22 publications

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“…The assumption of dynamically incompressible E × B flow fluctuations is justified for fluctuation frequencies below the acoustic characteristic frequency of GAM oscillations. As shown in Section 6, this frequency is about 40 kHz for the TJ-II plasmas under study, to be compared with typical zonal flow frequencies 10kHz [17,10].…”

Section: Neoclassical Equations and Simulationsmentioning

confidence: 99%

“…Note that we have dropped the inertia of the electrons, given their much lower mass, m e /m i 1, but kept the electron viscosity tensor as it cannot be neglected in our low-n, high-T e ECH-heated plasmas [18]. We work in Hamada magnetic coordinates (ψ, θ, ξ), and follow the notation of reference [10]. The lowest order incompressible ion flow is conveniently written as…”

Section: Neoclassical Equations and Simulationsmentioning

confidence: 99%

“…When a critical density n cr is reached, a spontaneous confinement transition takes place, associated with the formation of a shear layer. Experimentally, one of its most salient features is the emergence of zonal-flow-like electric potential structures [7,10]. When the density decreases, the reverse transition occurs at a similar n cr , but the amplitude of the zonal flows is smaller.…”

Section: Introductionmentioning

confidence: 99%

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Damping of radial electric field fluctuations in the TJ-II stellarator

Velasco¹,

Alonso²,

Calvo³

et al. 2013

Plasma Phys. Control. Fusion

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The drift kinetic equation is solved for low density TJ-II plasmas employing slowly varying, time-dependent profiles. This allows to simulate density ramp-up experiments and to describe from first principles the formation and physics of the radial electric field shear, which is associated to the transition from electron to ion root. We show that the range of frequencies of plasma potential fluctuations in which zonal flows are experimentally observed is neoclassically undamped in a neighborhood of the transition. This makes the electron root regime of stellarators, close to the transition to ion root, a propitious regime for the study of zonal-flow evolution. We present simulations of collisionless relaxation of zonal flows, in the sense of the Rosenbluth and Hinton test, that show an oscillatory behaviour in qualitative agreement with the experiment close to the transition.

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Section: Neoclassical Equations and Simulationsmentioning

confidence: 99%

Section: Neoclassical Equations and Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Damping of radial electric field fluctuations in the TJ-II stellarator

Velasco¹,

Alonso²,

Calvo³

et al. 2013

Plasma Phys. Control. Fusion

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“…In some experiments, bursty transport, Reynolds accelerations and edge flows have been shown to be linked. [12,13,[27][28][29] The role of blob and eddy tilting, also recently investigated in other studies [30][31][32], will be examined as both as a theoretical mechanism and a diagnostic of Reynolds stress in particular experimental discharges.…”

Section: Introductionmentioning

confidence: 98%

Edge sheared flows and the dynamics of blob-filaments

et al. 2013

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The edge and scrape-off-layer (SOL) region of a tokamak plasma is considered, with emphasis on sheared flow generation and the dynamics of blob-filaments. Both numerical simulations and experimental data analysis are employed. The simulations use the fluid-based 2D curvature-interchange model embedded in the SOLT code. A blob-tracking algorithm based on 2D time-resolved images from the gas puff imaging diagnostic has also been developed and applied to NSTX, Alcator C-Mod and simulation data. The algorithm is able to track the blob motion and changes in blob structure, such as elliptical deformations, that can be affected by sheared flows. Results of seeded blob simulations and quasi-steady turbulence simulations are compared with the experimental data to determine the role of plasma parameters on the blob tracks and to evaluate the exchange of momentum between the blobs and flows. The simulations are shown to reproduce many qualitative and quantitative features of the data including size, scale-length and direction of perpendicular (approximately poloidal) flows, the inferred Reynolds acceleration and residual stress, poloidal reversal of blob tracks, and blob trapping and/or ejection. Mechanisms related to blob motion, SOL currents and radial inhomogeneity are shown to be sufficient to explain the presence or absence of mean and oscillating zonal sheared flows in selected shots.

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“…[1]. In that reference, a method to extract the ZF component from a set of LRCed signals was introduced and tested.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of zonal-flow-like structures in the edge of the TJ-II stellarator

Alonso

Velasco

Arévalo

et al. 2012

Plasma Phys. Control. Fusion

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Abstract. The dynamics of fluctuating electric field structures in the edge of the TJ-II stellarator, that display zonal flow-like traits, is studied. These structures have been shown to be global and affect particle transport dynamically [1]. In this article we discuss possible drive (Reynolds stress) and damping (Neoclassical viscosity, geodesic transfer) mechanisms for the associated E × B velocity. We show that: (a) while the observed turbulence-driven forces can provide the necessary perpendicular acceleration, a causal relation could not be firmly established, possibly because of the locality of the Reynolds stress measurements, (b) the calculated neoclassical viscosity and damping times are comparable to the observed zonal flow relaxation times, and (c) although an accompanying density modulation is observed to be associated to the zonal flow, it is not consistent with the excitation of pressure side-bands, like those present in geodesic acoustic oscillations, caused by the compression of the E × B flow field.

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Dynamic transport regulation by zonal flow-like structures in the TJ-II stellarator

Cited by 15 publications

References 22 publications

Damping of radial electric field fluctuations in the TJ-II stellarator

Damping of radial electric field fluctuations in the TJ-II stellarator

Edge sheared flows and the dynamics of blob-filaments

Dynamics of zonal-flow-like structures in the edge of the TJ-II stellarator

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