Divertor geometry effects on detachment in TCV

Experimental observations and some preliminary results from B2-Eirene code modelling of divertor detachment in the TCV tokamak are reported, with emph asis on the aspects of this detachment related to divertor geometry. The co ntribution is restricted to deuterium fuelled ohmic plasmas for which the C B drift is directed away from the X-point of lower single-null, open divert ed equilibria with fixed elongation and triangularity. Unlike more conventi onal diverted equilibria, however, the configurations described are charact erised by both a very short divertor poloidal depth on a vertical target an d a very long poloidal depth on a horizontal target. Results are presented from density ramp discharges in which the outer (high poloidal depth) diver tor is already in the high recycling regime at the start of the density ram p and in which varying degrees of detachment are obtained depending on the magnitude of the imposed outer divertor flux expansion. In contrast, the in ner divertor remains in the large Dart attached for all densities. (C) 2001 Elsevier Science B.V. All rights reserved.