Spatial structure of the magnetic island plasma in the island divertor scrape-off layer in Wendelstein 7-X

The W7-X stellarator utilizes an island divertor, where the scrape-off layer (SOL) is formed by a chain of intrinsic magnetic islands that are intersected by (modular) divertor targets. Compared to a tokamak SOL, the island divertor SOL features a much more complex magnetic geometry and a fine-structured distribution of connection lengths that can reach up to 1km due to the small field line pitch angle. As a consequence, we observe a 3D distribution of plasma parameters (e.g. density, temperature, potential, electric fields) interplaying with 3D transport processes:

1. parallel transport in magnetic islands with long connection lengths implies poloidal transport on the island flux surface, effectively resulting in radial transport (in real space)

2. 2D drift flows (e.g. from stationary ExB drifts), as magnetic islands can have their own radial electric field (causing poloidal flow) and poloidal electric field (causing radial flow)

3. turbulent transport along pressure gradients: non-monotonic radial pressure profiles and significant poloidal pressure gradients across islands 

This contribution summarizes first key findings from the (recently concluded) first W7-X operation phase with fully cooled divertor. The diagnostic focus is on a reciprocating 2D poloidal-radial array of electric probes, which sheds light into the spatial structure of plasma parameters, 2D electric fields, and the role of turbulence and quasi-periodic modes for perpendicular transport.