SHOCK FORMATION IN A POLOIDALLY ROTATING TOKAMAK PLASMA

When the Mach number M(p) of the poloidal rotation in a tokamak approaches unity, the poloidal variations of plasma density and potential appear to have the characteristics of a shock whose front lies on a plane (ribbon) of a fixed poloidal angle eta-0. The shock first appears, when 1 - M(p) less-than-or-similar-to square-root epsilon (epsilon is the inverse aspect ratio), on the inside of the torus at a shock angle eta-0 greater-than-or-equal-to pi if the plasma rotates counterclockwise poloidally. As M(p) increases, eta-0 moves in the direction of the poloidal rotation. At M(p) = 1, eta-0 = 2-pi. When M(p) - 1 less-than-or-similar-to square-root epsilon, the shock angle is at eta-0 less-than-or-similar-to pi. The parallel viscosity associated with the shock is collisionality independent, in contrast to the conventional neoclassical viscosity. The viscosity reaches its maximum at M(p) = 1, which is the barrier that must be overcome to have a poloidal supersonic flow. Strong up-down asymmetric components of poloidal variations of plasma density and potential develop at M(p) congruent-to 1. In the edge region, the convective poloidal momentum transport weakens the parallel viscosity and facilitates the L-H transition.