First modelling of the textor DED near field divertor

As the first step in the modelling of the plasma-wall interaction of the proposed dynamic ergodic, divertor (DED) of TEXTOR-94, the topology of the magnetic field lines of the divertor is analysed. Despite the strong ergodization, the magnetic field lines intersecting the wall in one poloidal turn form continuous sets. These sets are visualized by a two dimensional (2-D) imaging technique; the field lines are traced one poloidal turn clockwise and counter-clockwise from the outer midplane, marking those lines intersecting the wall. An overlay of the marked starting points defines areas with the properties of a scrape-off layer (SOL) and areas with field lines ending on one side in the ergodic layer and one side on the wall. The edge plasma can be described by a 2-D model; the model treats part of the plasma as that of a conventional SOL and another part as that with 'half open' field lines connecting the divertor target plate with the ergodic layer. Calculations of the power flux distribution in the DED near field divertor are presented.