SPONTANEOUS POLOIDAL SPIN-UP OF TOKAMAK PLASMAS - REDUCED EQUATIONS, PHYSICAL-MECHANISM, AND SONIC REGIMES

A theoretical description of the spontaneous (Stringer) poloidal spin- up of tokamak plasmas is given. A set of reduced equations is derived to investigate various aspects of the phenomenon. A simple physical de scription of the instability mechanism is given. The theory of the ins tability is extended to show that the spin-up persists even under cond itions where the growth rate is sonic. A nonlinear evolution equation for unstable poloidal rotation is obtained which shows that the instab ility mechanism loses its efficacy when the poloidal speed exceeds the poloidal sound speed, thus resulting in nonlinear saturation of the r otation at this level.