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 emphasis on the aspects of this detachment related to divertor geometry. The contribution is restricted to deuterium fuelled, ohmic plasmas for which the ∇B drift is directed away from the X-point of lower single-null, open diverted equilibria with fixed elongation and triangularity. Unlike more conventional diverted equilibria, however, the configurations described are characterised by both a very short divertor poloidal depth on a vertical target and a very long poloidal depth on a horizontal target. Results are presented from density ramp discharges in which the outer (high poloidal depth) divertor is already in the high recycling regime at the start of the density ramp and in which varying degrees of detachment are obtained depending on the magnitude of the imposed outer divertor flux expansion. In contrast, the inner divertor remains in the large part attached for all densities.