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Center for Nonlinear Studies |
Finite toroidal and poloidal flows are routinely observed in the edge plasma region of tokamak experiments. MHD theory predicts that when the poloidal velocity is transonic with respect to the poloidal sound speed (csp csBp=B, where Bp is the poloidal field) transient shocks will develop in the transonic region. The shocks will then move in the poloidal direction and disappear once they reach the location of the minimum transverse flow cross section. After the end of the transient, a steady-state pedestal in plasma density and pressure is left, with the height of the pedestal depending on the poloidal location. Equilibrium models have been used to calculate ideal transonic equilibria with discontinuous density and pressure profiles. Time-dependent simulations show that the transonic equilibrium state is dynamically accessible in the frame of the resistive MHD model. Both equilibrium and time-dependent results are in agreement with the prediction of theory. In the present work, equilibrium and time-dependent models and simulations are discussed. It is shown how equilibrium and steady-state pedestal-like discontinuous profiles are generated in realistic configurations (including X-points and o en field line regions). A possible connection to the initial phase of the L-H transition is argued. Work supported by US Department of Energy Contract No. DE-FG02-93ER54215
Host: Gian Luca Delzanno, T-5, 667-2604