UP-DOWN SYMMETRY IN DOUBLE NULL DIVERTOR EXPERIMENTS AND MAGNETIC-FIELD TOPOLOGY

The effect of up-down asymmetries is considered for transport in a double null divertor geometry. Particular attention is paid to the type of asymmetries associated with a disconnection of the two X points, which cause differences in the flows to the top and bottom diverters. Examples are given of the conditions under which such asymmetries arise, and quantitative estimates of transport are made. The sensitivity to these asymmetries is such that they seriously complicate the quantitative interpretation of transport experiments conducted in double null geometry.