Thermodynamical and microscopic properties of turbulent transport in the edge plasma

Ghendrih, Ph.; Norscini, C.; Hasenbeck, F.; Dif‐Pradalier, G.; Abiteboul, J.; Cartier-Michaud, Thomas; Garbet, X.; Grandgirard, V.; Marandet, Y.; Sarazin, Y.; Tamain, P.; Zarzoso, D.

doi:10.1088/1742-6596/401/1/012007

Cited by 9 publications

(17 citation statements)

References 8 publications

(11 reference statements)

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“…Strong stiffness indeed impedes nonlocal turbulence propagation and especially turbulence spreading [45], a possibly important ingredient to the shortfall problem [46]; (iv) the fact that large though highly intermittent flux-driven fluxes are observed at low temperature gradient drives (location [0]) where both the gradient-driven flux and its statistical variations remain small tends to indicate clear sensitivity of the flux-gradient relation to temporal coarse-graining, despite the fact that the present results are flux-surface averaged and thus already strongly spatially coarse-grained. This result echoes results in [47,48].…”

Section: Impact On Profile Stiffness and Heat Fluxessupporting

confidence: 88%

The E × B staircase of magnetised plasmas

Dif‐Pradalier¹,

Hornung²,

Garbet³

et al. 2017

Nucl. Fusion

117

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We show that a class of near-marginal and low-collisional magnetised plasmas naturally evolve into a globally organised state dubbed the ' × E B staircase'. A key signature of this self-organised state is the containment of avalanche activity, detrimental for confinement, by a series of microbarriers for transport, the staircase steps, beneficial for confinement. Conditions for existence of the × E B staircase, impact on transport and confinement and robustness in parameter space are discussed.

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Section: Impact On Profile Stiffness and Heat Fluxessupporting

confidence: 88%

The E × B staircase of magnetised plasmas

Dif‐Pradalier¹,

Hornung²,

Garbet³

et al. 2017

Nucl. Fusion

117

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“…The conclusion of our analysis have to be set in this perspective, which combines very large data handling but incomplete description, as well as long simulation time but still insufficient statistics. These are required to capture significantly the events that prevail in the heavy tails that characterise turbulence self-organisation [33].…”

Section: Discussionmentioning

confidence: 99%

Phase space structures in gyrokinetic simulations of fusion plasma turbulence

et al. 2014

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Gyrokinetic simulations of fusion plasmas give extensive information in 5D on turbulence and transport. This paper highlights a few of these challenging physics in global, flux driven simulations using experimental inputs from Tore Supra shot TS45511. The electrostatic gyrokinetic code GYSELA is used for these simulations. The 3D structure of avalanches indicate that these structures propagate radially at localised toroidal angles and then expand along the field line at sound speed to form the filaments. Analysing the poloidal mode structure of the potential fluctuations (at a given toroidal location), one finds that the low modes m = 0 and m = 1 exhibit a global structure; the magnitude of the m = 0 mode is much larger than that of the m = 1 mode. The shear layers of the corrugation structures are thus found to be dominated by the m = 0 contribution, that are comparable to that of the zonal flows. This global mode seems to localise the m = 2 mode but has little effect on the localisation of the higher mode numbers. However when analysing the pulsation of the latter modes one finds that all modes exhibit a similar phase velocity, comparable to the local zonal flow velocity. The consequent dispersion like relation between the modes pulsation and the mode numbers provides a means to measure the zonal flow. Temperature fluctuations and the turbulent heat flux are localised between the corrugation structures. Temperature fluctuations are found to exhibit two scales, small fluctuations that are localised by the corrugation shear layers, and appear to bounce back and forth radially, and large fluctuations, also readily observed on the flux, which are associated to the disruption of the corrugations. The radial ballistic velocity of both avalanche events if of the order of 0.5ρ * c0 where ρ * = ρ0/a, a being the tokamak minor radius and ρ0 being the characteristic Larmor radius, ρ0 = c0/Ω0. c0 is the reference ion thermal velocity and Ω0 = qiB0/mi the reference ion Larmor frequency for the characteristic amplitude of the magnetic field B0, qi and mi being respectively the ion charge and mass. The electric drift velocity is also found to exhibit a poloidal pattern, with maximum amplitude of the fluctuations either in the top or in the bottom regions of the machine depending on the sign of the zonal flow shear. This effect is found to be correlated to the stopping capability of the corrugation structures. The neoclassical properties stemming from the trapped particle drifts lead to large distortion of the distribution function. As expected, these prevail at the outer part of the simulation region despite the large collisionality. The distribution function fluctuations appear to be aligned along the v = constant lines at constant poloidal angle. A specific symmetry is observed regarding the interplay of turbulence with the trapped-passing region.

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“…The chosen coarse graining time scale τ cg is therefore in the range of a second while the turbulence time scales τ turb are usually assumed to range between microseconds and milliseconds. It is to be noted however that in flux driven turbulence simulations, no spectral gap is observed between this turbulence time range and the macroscopic time τ cg [35]. This can be an issue in the coarse graining procedure [35].…”

Section: Introductionmentioning

confidence: 94%

“…As final remark, one must keep in mind that the apparent universality of diffusive transport models is connected to the fact that it is in practice the simplest local transport model, together with ballistic transport, which can be implemented in equations. While ballistic transport questions the connection to the departure from thermodynamic equilibrium [35], non-linear dependencies of the diffusion coefficient, as with the κ-ε model, can drive transport properties that depart significantly from that of constant diffusion processes. As stated in the introduction, one can then expect that the use of a κ-ε model for plasma-wall interaction can improve the model consistency and predictive ability.…”

Section: Introductionmentioning

confidence: 99%

Self-consistent cross-field transport model for core and edge plasma transport

Baschetti

Bufferand²,

Ciraolo³

et al. 2021

Nucl. Fusion

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The 2D mean-field plasma edge transport description of plasma wall interaction is completed by a κ-ε model as in Reynolds Average Navier Stokes simulations for neutral fluids. The local evolution of the turbulent kinetic energy κ and its dissipation rate ε are revisited and slightly modified. It is shown that the κ-ε extends the quasilinear approach by self-consistently determining κ and the relevant time κ/ε leading to the diffusion coefficient κ 2 /ε. The κ-ε evolution is also shown to be equivalent to both coupled Ginzburg-Landau amplitude equations and predator-prey systems where κ is the prey and ε the predator. The dissipation process ε we enforce describes the small scale dissipation of Kolmogorov cascades. It depends on a free parameter akin to a velocity V . The chosen closure relates V to the the parallel connection time and the normalized Scrape-Off layer width qρ * , q is the safety factor and ρ * the ratio of the characteristic Larmor radius and plasma minor radius. A 1D model with κ-ε self-organized transport is used for comparison to empirical scaling laws of SOL width and energy confinement time in L-mode plasmas. Shortfalls of the scaling laws are analyzed. Possible changes of the closure for V are discussed. The 1D model is also used to test the transport response to a dependence of V to large scale velocity shear. Spontaneous confinement improvement when increasing the heating power 1 is observed with the development of an interface barrier at the separatrix. Plasma-wall interaction simulations for TCV and WEST are analyzed. A single scalar free parameter tunes the cross field transport. Experimental midplane and divertor profiles are compared to the simulations. Remarkable agreement is observed. The SOL width determined by the simulation for WEST is close to the experimental value with less than 20 % difference, while the scaling law for L-mode is off my more than a factor 3. The turbulent transport described by the κ-ε is not homogeneous, but ballooned as experimentally observed together with cross-field transport in the divertor SOL on the low field side, and nearly none in the private flux region.

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Thermodynamical and microscopic properties of turbulent transport in the edge plasma

Cited by 9 publications

References 8 publications

The E × B staircase of magnetised plasmas

The E × B staircase of magnetised plasmas

Phase space structures in gyrokinetic simulations of fusion plasma turbulence

Self-consistent cross-field transport model for core and edge plasma transport

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