Modeling of the dynamic ergodic divertor of TEXTOR-94

Abstract

A Dynamic Ergodic Divertor (DED) is under construction for TEXTOR-94. The ergodization will be achieved by a set of 16 in-vessel perturbation – plus two compensation – coils located at the high field side of TEXTOR-94. The coils follow helically the resonant magnetic field lines for one toroidal turn and are individually fed outside the vessel allowing a large flexibility for possible connections. The DED-system will operate at dc or several fixed frequencies up to 10 kHz. Different and adapted modeling efforts have been undertaken both for the ergodic area and the laminar zone. The basic techniques for the ergodic zone are field line mapping and field line tracing; the analysis provides the magnetic field structure in form of Poincaré plots and the transport coefficients for the magnetic field lines. For the laminar zone a modeling is used which takes into account the typical aspects of the scrape-off layer physics. A low frequency operation of the DED will distribute the heat flux over the relatively large area of the divertor target plate. The calculations show that the high frequency operation should impose a torque on the plasma edge which is of similar size as the one imposed by tangential NBI.