Radial discontinuities in tokamak magnetohydrodynamic equilibria with poloidal flow

It is shown that transonic poloidal flow leads to ideal magnetohydrodynamic tokamak equilibria with radial discontinuities in the density, pressure, and flow velocity profiles. Transonic profiles are defined as having flow velocities ranging from subsonic to supersonic with respect to the poloidal sound speed (c(s)B(p)/B). The jump of the equilibrium quantities occurs approximately at the sonic surface and its magnitude is of order epsilon(1/2) (epsilon is the inverse aspect ratio). Because of the large velocity shear at the sonic surface, transonic profiles may improve energy confinement as suggested by current understanding of tokamak plasma turbulence suppression. (C) 2000 American Institute of Physics. [S1070-664X(00)00506-1].