On the origin of anomalous radial transport in the tokamak SOL

Turbulent transport in the scrape-off layer of TCV has been investigated by probe measurements and direct comparison with two-dimensional fluid simulations of interchange motions at the outer midplane. The experiments demonstrate that the fluctuation statistics in the region where plasma profiles are broad are invariant with respect to changes in the line-averaged core plasma density. Good agreement is found between measurements and an interchange turbulence simulation at high density, indicating that the turbulent transport is dominated by the radial motion of field-aligned plasma filaments. Moreover, the plasma flux onto the main chamber wall at the outer midplane scales linearly with the local particle density, implying that the particle flux at the wall radius can be parameterized in terms of an effective convection velocity. Strong ballooning of the edge turbulence would also result in toroidal field direction independent transport-driven parallel flows in the scrape-off layer. The magnitude of this flow estimated from pressure fluctuation statistics in the simulations is found to compare favorably with the measured flow offset obtained when averaging data obtained from flow profiles observed in matched forward and reversed field discharges.