Measurement and simulation of edge flows induced by ergodization in Tore Supra

Test particle simulations are used to model edge flows in the ergodic diver tor of Tore Supra. The field line tracing code MASTOC is used to calculate the full 3D magnetic geometry. The model assumes ballistic guiding center m otion along the magnetic field lines with cross-freld transport represented by a random walk process. Large flows of alternating direction are found i n the laminar zone. The flow pattern displays the m = 18 poloidal mode numb er imposed by the divertor coils. Some of the flow is due to magnetic conne ctions to neutralizer plates, while some is due to preferential channeling of particle flux from the ergodic layer. The measured radial extent of the flow pattern and the appearance of flow reversal at the Gundestrup probe lo cation are well described by the simulations and is simply related to the c onnection length map. The flows should influence impurity transport via the drag force: we present preliminary test particle simulations of impurity i on transport within the 3D flow patterns. Divertor operation leads to an im provement of impurity screening with respect to the limiter case if the imp urities are ionized within the laminar zone. (C) 2001 Elsevier Science B.V. All rights reserved.