Electron temperature gradient induced instability in tokamak scrape-off layers

Berk, H. L.; Cohen, R. H.; Ryutov, D. D.; Tsidulko, Yu. A.; Xu, X. Q.

doi:10.1088/0029-5515/33/2/i07

Cited by 82 publications

(67 citation statements)

References 14 publications

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“…These blobs are the nonlinear limit of the conductingwall temperature-gradient modes described in Ref. [21]. The terminal velocity in the case where this drive dominates over curvature drive (valid for ΛaRF a /ρ i L c > 1, where…”

Section: Blobsmentioning

confidence: 86%

Theory and fluid simulations of boundary-plasma fluctuations

et al. 2007

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Abstract. Theoretical and computational investigations are presented of boundaryplasma microturbulence that take into account important effects of the geometry of diverted tokamaks -in particular, the effect of x-point magnetic shear and the termination of field lines on divertor plates. We first generalize our previous "heuristic boundary condition" which describes, in a lumped model, the closure of currents in the vicinity of the x-point region to encompass three current-closure mechanisms. We then use this boundary condition to derive the dispersion relation for low-beta flutelike modes in the divertor-leg region under the combined drives of curvature, sheath impedance, and divertor tilt effects. The results indicate the possibility of strongly growing instabilities, driven by sheath boundary conditions, and localized in either the private or common flux region of the divertor leg depending on the radial tilt of divertor plates. We re-visit the issue of x-point effects on blobs, examining the transition from blobs terminated by x-point shear to blobs that extend over both the main SOL and divertor legs. We find that, for a main-SOL blob, this transition occurs without a free-acceleration period as previously thought, with x-point termination conditions applying until the blob has expanded to reach the divertor plate. We also derive propagation speeds for divertor-leg blobs. Finally, we present fluid simulations of the C-Mod tokamak from the BOUT edge fluid turbulence code, which show main-SOL blob structures with similar spatial characteristics to those observed in the experiemnt, and also simulations which illlustrate the possibility of fluctuations confined to divertor legs.

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Section: Blobsmentioning

confidence: 86%

Theory and fluid simulations of boundary-plasma fluctuations

et al. 2007

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“…Apart from the fluctuations caused by the 'standard' edge plasma turbulence including blobs that are originated somewhere inside the separatrix, the peculiar conditions in the SOL plasma contacting the material surfaces can drive some specific instabilities (see e.g. Nedospasov 1989;Berk et al 1993;Cohen & Ryutov 1996). Moreover, some peculiarities of the detached plasmas (including the detachment front, strong impurity radiation, the large volume of a cold, ∼eV, plasma, etc.)…”

Section: Transient Effects In the Detached Divertor Regimementioning

confidence: 99%

Physics of ultimate detachment of a tokamak divertor plasma

Krasheninnikov¹,

2017

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The basic physics of the processes playing the most important role in divertor plasma detachment is reviewed. The models used in the two-dimensional edge plasma transport codes that are widely used to address different issues of the edge plasma physics and to simulate the experimental data, as well as the numerical schemes and convergence issues, are described. The processes leading to ultimate divertor plasma detachment, the transition to and the stability of the detached regime, as well as the impact of the magnetic configuration and divertor geometry on detachment, are considered. A consistent, integral physical picture of ultimate detachment of a tokamak divertor plasma is developed.

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“…due to magnetic shear near the X-point, then it is natural to compare to instabilities that are localized near the target plates. The fastest growing linear modes that have been identified near the target plate are the sheath modes (SH), which are are driven by the electron temperature gradient and destabilized by the presence of the highly conducting sheath at the end walls [21,22,26,27]. The sheath boundary layer implies that the background equilibrium poloidal velocity V p ∼ Λρ s c s /r T near the target plate has the same scale variation as the electric field, and thus, the electron temperature: r V = V p /V p ∼ r E ∼ r T .…”

Section: Requirements For Generation Of Additional Turbulent Transmentioning

confidence: 99%

Generation of non-axisymmetric scrape-off layer perturbations for controlling tokamak edge plasma profiles and stability

et al. 2012

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A critical requirement for tokamak fusion reactors is the control of the divertor heat load, both the time-averaged value and the impulsive fluxes that accompany edge-localized modes. We propose driving toroidally varying currents through the scrape-off layer (SOL) plasma both to broaden the SOL by inducing radial convection and to control the edge pressure gradient by inducing resonant magnetic perturbations. The generation of additional convective transport via steady-state convective cells or increased turbulence drive requires that the electric potential perturbations exceed a threshold in amplitude that depends on wavelength. The generation of a coherent magnetic perturbation is optimized by choosing the appropriate width and phasing of the biasing region at the target plate in order to optimize the profile of the SOL current. Longer wavelength modes produce a larger effect because they are not sheared as strongly by the magnetic X-point. Generation of the necessary currents is challenging due to the possibly substantial power requirements and the possible need for internal insulators. We analyze passive current-drive mechanisms that rely on puffing and pumping of neutral gas in a toroidally asymmetric fashion using the UEDGE code to model the ITER divertor.

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Electron temperature gradient induced instability in tokamak scrape-off layers

Cited by 82 publications

References 14 publications

Theory and fluid simulations of boundary-plasma fluctuations

Theory and fluid simulations of boundary-plasma fluctuations

Physics of ultimate detachment of a tokamak divertor plasma

Generation of non-axisymmetric scrape-off layer perturbations for controlling tokamak edge plasma profiles and stability

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