3D study of energy transport and role of stochasticity in the W7-X edge

The magnetic structures of W7-X edge configurations typically exhibit ergodic regions of different radial extent, where the radial plasma heat transport might be expected to be a combined effect of intrinsic anomalous diffusion and stochastic transport due to radially diffusing magnetic field lines. This question has been investigated by a dedicated numerical study of the energy transport performed with the EMC3 edge plasma transport code applied to three W7-X configurations of major interest. Both the calculated temperature profiles and heat load distributions on the divertor plates show that, contrary to simple collisionless estimates predicting a significant stochastic transport, the heat transport is dominated by intrinsic anomalous diffusion even for very small values of the transport coefficient. This behavior could be explained using an improved estimate including collisional transport