Blob Transport at High Collisionality and the SOL Density Limit

TL;DRAbstract

This paper describes recent developments in the theory of blob transport at high collisionality, Λ = (νeiL||/ρsΩe) ~ 1, and its application to the convective density limit on Alcator C-Mod. The original sheath-connected blob model1 described how coherent structures created by edge turbulence would charge up (due to ∇B and curvature drifts) and E×B drift across the far SOL. This model accounted for several qualitative observations about SOL turbulence, such as its spatial and temporal intermittency and non-diffusive SOL transport of particles and energy. Several other blob parameter regimes have been identified,2 which are relevant in the highly turbulent blob creation zone in the near SOL. In each regime, the radial blob velocity vx has a known scaling with plasma parameters and with the blob radius ab. This picture is unified by a simple correspondence rule between the linear dispersion relation of the underlying instability driving the turbulence and the blob parameters:

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