Neoclassical theory of rotation and electric field in high collisionality plasmas with steep gradients

The equation describing the radial transport of toroidal momentum in a collisional subsonic plasma with steep gradients has been obtained via a systematic expansion of the two-fluid equations. The diffusion rate is classical; the poloidal rotation, driven by the temperature gradient, generates, in turn, a toroidal flow gradient, also in Ohmic discharges. Moreover, important modifications of the parallel momentum equation are found to arise if L1[(n i /V i)(q R/rLT) is >O(1/3); the poloidal rotation velocity is then no longer unique but obeys a cubic equation which may allow for bifurcated equilibria under certain conditions. The toroidal velocities predicted for Ohmic discharges compare well with those measured in PLT @Princeton Large Torus; S. Suckewer et al., Nucl. Fusion 21, 1301 ~1981!#; the relevance of the extended equation providing the poloidal rotation velocity to selected experimental edge plasmas is discussed. © 2000 American Institute of Physics. @S1070-664X~00!04009-X#