Numerical marfe studies for a deuterium-carbon plasma at ASDEX upgrade

Marfes-axisymmetric, poloidally localized plasma edge phenomena occurring in tokamaks close to the upper density limit-are studied numerically for a realistic ASDEX-upgrade single-null divertor geometry. An advanced version of the 2D tokamak edge multifluid code B2 is used, assuming plausible boundary conditions and radial transport laws. A deuterium plasma contaminated with carbon is chosen, since carbon is the most prominent impurity in tokamaks with graphite tiles and some form of oxygen gettering. All charge states are treated as separate fluids. The formation of a marfe and its nonlinear behaviour is investigated in detail for realistic experimental scenarios. It is shown that a marfe may be readily stabilized by external feedback control using the radiated power as the control parameter. The whole set of stationary states can be represented in a diagram of steady states by a double-valued function, where the two branches describe marfe-free and marfe plasma states, respectively. The internal mechanism sustaining a state steady marfe, i.e. a localized region of enhanced density and lowered temperature relative to the surrounding medium, is discussed.