Turbulence spreading into the linearly stable zone and transport scaling

Hahm, T.S.; Diamond, P. H.; Zhang, Lin; Itoh, K.; Itoh, Sanae I.

doi:10.1088/0741-3335/46/5a/036

Cited by 204 publications

(225 citation statements)

References 39 publications

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“…For drift waves, we can approximate e Ͼ / T e ϳ 1/͑k Ќ L n ͒, where L n is the perpendicular length scale over which the density varies. The magnitude of the turbulent viscosity can then be estimated to be 12 , this condition will nearly always be satisfied. Thus, in practical terms, the turbulent stresses always exceed inertia.…”

Section: Closure Of Drift Wave-tearing Mode Systemmentioning

confidence: 98%

Multiscale interaction of a tearing mode with drift wave turbulence: A minimal self-consistent model

McDevitt

Diamond

2006

Physics of Plasmas

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A minimal self-consistent model of the multiscale interaction of a tearing mode with drift wave turbulence is presented. A tearing instability in a cylindrical plasma interacting with electrostatic drift waves is considered, for reasons of simplicity. Wave kinetics and adiabatic theory are used to treat the feedback of tearing mode flows on the drift waves via shearing and radial advection. The stresses exerted by the self-consistently evolved drift wave population density on the tearing mode are calculated by mean field methods. The principal effect of the drift waves is to pump the resonant low-m mode via a negative viscosity, consistent with the classical notion of an inverse cascade in quasi-two-dimensional turbulence. This process can occur alone or in synergy with current gradient drive of the low-m mode. Speculations of the relation of this multiscale process to the more general issue of the fate of energy transferred to large scales by an inverse cascade are presented. The existence of nonlinearly driven vortices pinned to low-q surfaces as a class of highly anisotropic dissipative structures which terminate the inverse cascade is proposed. The evolution of a finite size magnetic island is discussed.

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Section: Closure Of Drift Wave-tearing Mode Systemmentioning

confidence: 98%

Multiscale interaction of a tearing mode with drift wave turbulence: A minimal self-consistent model

McDevitt

Diamond

2006

Physics of Plasmas

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“…This under-prediction of transport is sometimes referred to as the "transport shortfall" conundrum and though various attempts have been made to address it [16], its understanding remains troublesome. The way a hot stiff core interplays with the plasma edge is a central issue to combine high fusion performance and safe diverter operation.The "spreading" of turbulence [17], i.e. the spacetime propagation of patches of turbulence activity originated elsewhere in the plasma volume is amongst the possible mandatory ingredients to address this conundrum.…”

mentioning

confidence: 99%

“…The "spreading" of turbulence [17], i.e. the spacetime propagation of patches of turbulence activity originated elsewhere in the plasma volume is amongst the possible mandatory ingredients to address this conundrum.…”

mentioning

confidence: 99%

Evidence for Global Edge–Core Interplay in Fusion Plasmas

Dif‐Pradalier

Caschera²,

Ghendrih³

et al. 2017

Plasma and Fusion Research

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Large-scale reactor-relevant fusion plasmas are likely to operate near marginal stability. In this regime, we show clear evidence of interplay between core and edge regions of the plasma. This result illustrates aspects of the controversial 'shortfall problem' in the far-core, near-edge so-called 'No Man's Land' region and a possible route to resolve this issue. More generally, it emphasises global-scale organisation of turbulence and relevance of edge dynamics to core confinement. Magnetically confined plasmas are often separated in spirit and in modeling into an inner core region of fusion performance and a somewhat outlying and disconnected edge and Scrape-Off-Layer (SOL) region, dedicated to interactions with the material structure of the confining device. The degree to which it is actually reasonable to disconnect core and edge is addressed in this paper. Conclusions are threefold: (i) core and edge can significantly interplay, hence global-scale description of turbulence selforganisation appears important, (ii) inward propagation of edge turbulence is a major contribution to core-edge interplay, (iii) this interplay is all the more important close to a critical point, marginal instability for instance.The regime of near-marginality [1] for magnetised plasmas is not merely academically-appealing for its rich dynamics and manifestations of self-organisation [2][3][4][5][6][7][8]. It is as well a likely practical operating regime for current and future confinement devices for which the ratio of plasma volume over external heating is large, favouring proximity to marginality. Whilst a submarginal state may exist globally, a regime of near-marginality is frequently inhomogeneous in time and in space, displaying a range of transport properties [9] as submarginal and turbulent patches coexist, with intermittent behaviour. Global-scale organisation of turbulence, from core (ρ = r/a 0.6) to edge (0.9 ρ 1) is here investigated in such regimes, in the relevant low-heating limit of flux-driven forcing and using the gyrokinetic approach in Gysela [10,11].Gysela has recently been upgraded to account beyond the outer edge for SOL-like (ρ ≥ 1) boundary conditions [12]. A sink is progressively added from ρ = 1.05 to 1.15 author's e-mail: guilhem.dif-pradalier@cea.fr * ) This article is based on the invited talk at the 33rd JSPF Annual Meeting (2016, Tohoku).by enforcing exponentially-decaying density and temperature profiles. Though too crude to address SOL physics, these outer conditions introduce a coupling between the modeled confined plasma and the SOL-like sink region. Outward and inward plasma fluxes are self-consistently exchanged across ρ = 1 and fluxes beyond ρ = 1.05 are progressively damped. Self-consistent interplay of core and edge can be realistically investigated up to ρ = 1. The steady increase, in L-mode, of the relative level of turbulent fluctuations δn/n, n being the plasma density, from the innermost core to the edge [13] is a universal feature of tokamak plasmas. Yet under-prediction of the fluctuatio...

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“…Bohm-like scaling may be expected and is relevant to several scenarios, including turbulence spreading [41][42][43] from the linearly active ͑unstable͒ region to the linearly inactive ͑stable͒ region. The standard approach involves a random walk type of picture for diffusive processes using the scale length of streamer structure as the step size ͑close to the system size ⌬ when streamers dominates͒ and a time correlation of d0 −1 as the time step.…”

Section: F Transport Scalingmentioning

confidence: 99%

Streamer-induced transport in the presence of trapped ion modes in tokamak plasmas

et al. 2010

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Global gyrokinetic Vlasov simulations for trapped ion modes are performed by solving a Vlasov equation averaged over the cyclotron and bounce motions of trapped ions. The distribution function, for trapped ions, is then calculated in a two-dimensional phase space, parametrized by the longitudinal action ͑energy͒ and the magnetic moment in presence of magnetic shear. The physical mechanism of the saturation processes between streamerlike structures and zonal flows in relation to the suppression of turbulent transport is discussed. The magnetic shear is identified to play a key role in the dominant streamer-induced transport regime, which exhibits a Bohm-like scaling. The interaction of streamerlike structures with plasma turbulence is shown to produce the inverse cascade that condenses onto long-wavelength trapped ion structures, on the basis on wave triad interactions.

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Turbulence spreading into the linearly stable zone and transport scaling

Cited by 204 publications

References 39 publications

Multiscale interaction of a tearing mode with drift wave turbulence: A minimal self-consistent model

Multiscale interaction of a tearing mode with drift wave turbulence: A minimal self-consistent model

Evidence for Global Edge–Core Interplay in Fusion Plasmas

Streamer-induced transport in the presence of trapped ion modes in tokamak plasmas

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