  The structure of poloidal and toroidal flows of trace impurities in the edge
pedestal of tokamak plasmas is studied analytically and numerically. Parallel
momentum balance is analysed upon retaining the following terms: poloidal and
toroidal centrifugal forces (inertia), pressure force, electric force, and the
friction force. It is shown that, when the poloidal flow is such to produce a
properly defined Mach number of order unity somewhere on the flux surface,
shock fronts can form. The shock fronts can modify the predicted asymmetry
structures in both the flow and the density profile along the poloidal arc.
Predictions of the theory are shown against experimental observations in the
ASDEX Upgrade tokamak, showing good qualitative and quantitative agreement if
the inertia term associated with the poloidal flow is retained.

Plasma Physics