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This paper studies the turbulent kinetic energy ($k_\perp$) in 2D isothermalelectrostatic interchange-dominated ExB drift turbulence in the scrape-offlayer and its relation to particle transport. An evolution equation for theformer is analytically derived from the underlying turbulence equations.Evaluating this equation shows that the dominant source for the turbulentkinetic energy is due to interchange drive, while the parallel current loss tothe sheath constitutes the main sink. Perpendicular transport of the turbulentkinetic energy seems to play a minor role in the balance equation. Reynoldsstress energy transfer also seems to be negligible, presumably because nosignificant shear flow develops under the given assumptions of isothermalsheath-limited conditions in the open field line region. The interchange sourceof the turbulence is analytically related to the average turbulent ExB energyflux, while a regression analysis of TOKAM2D data suggests a model that islinear in the turbulent kinetic energy for the sheath loss. A similarregression analysis yields a diffusive model for the average radial particleflux, in which the anomalous diffusion coefficient scales with the square rootof the turbulent kinetic energy. Combining these three components, a closed setof equations for the mean-field particle transport is obtained, in which thesource of the turbulence depends on mean flow gradients and $k_\perp$ throughthe particle flux, while the turbulence is saturated by parallel losses to thesheath. Implementation of this new model in a 1D mean-field code shows goodagreement with the original TOKAM2D data over a range of model parameters.

physics of plasmas

Turbulent kinetic energy in 2D isothermal interchange-dominated  scrape-off layer ExB drift turbulence: Governing equation and relation to  particle transport