The role of particle drifts in W7-X divertor heat load asymmetries

In both tokamaks and stellarators, particle drifts in the scrape-off layer are known to affect the heat load distribution on the divertor targets. In W7-AS, for example, divertor heat loads were sometimes observed to be greater by up to a factor of two in regions downstream relative to the ExB drift [1]. In the first divertor experiments in W7-X we have observed indications of similar asymmetries, which appear to shift in response to reversal of the magnetic field. We present probe measurements from the upper and lower W7-X divertors, as well as measurements of upstream scrape-off layer parameters including plasma flow and radial electric field.

[1] Y. Feng et al., Plasma Phys. Control. Fusion 40 (1998), 371