POLOIDAL ROTATION OF TOKAMAK PLASMAS AT SUPER POLOIDAL SONIC SPEEDS

A tokamak plasma rotating poloidally at speeds in excess of the poloid al sound speed is studied. The study is motivated by the propositions that shear in the rotation could suppress turbulence and improve confi nement and that the poloidal sound speed is the critical speed to exce ed for flow profiles distributed over the entire minor radius. For suc h rapidly rotating plasma regimes, the Grad-Shafranov equation is exam ined, the damping rate of the rotation is calculated, particle orbits are investigated, and a heuristic MHD stability study is done. It is f ound that for rotation speeds exceeding the poloidal sound speed but l ess than the poloidal Alfven speed no deleterious effects can be expec ted from the rapid rotation as regards equilibrium or MHD stability. T he damping rate of poloidal rotation is shown to fall off over the pea k rate, in all collisionality regimes, as u(p)(-2). This feature makes more efficacious the external driving of such poloidal flow and allow s favourable extrapolation to reactor relevant regimes. Finally, it is shown that the fraction of trapped ions is significantly depleted in this regime, suggesting a reduction in the neoclassical heat transport as well.