Magnetic topology effects on Alcator C-Mod flows

The effect of magnetic topology on ion and impurity flows in a tokamak is considered by investigating the consequences of (i) the reversal of toroidal and poloidal magnetic fields and currents; (ii) a switch from lower to upper X-point operation; (iii) poloidal magnetic field or plasma current reversal, and (iv) toroidal magnetic field reversal. The general symmetries associated with magnetic topology changes in tokamaks are employed to demonstrate that the flux surface flows inside and outside the separatrix observed in Alcator C-Mod [I. H. Hutchinson , Phys. Plasmas 1, 1511 (1994)] can be used to determine the flow features, including neoclassical and turbulent effects and in the presence of charge exchange. (c) 2006 American Institute of Physics.