Transitions to an enhanced confinement regime in tokamak plasmas with
negative central magnetic shear have been observed in a number of devi
ces. A simple model incorporating the nonlinear coupling between the t
urbulent fluctuations and the sheared radial electric field is added t
o a transport model in order to investigate the dynamics of the transi
tion to this enhanced confinement mode. In this model, by incorporatin
g; both the instability growth rate profiles and particle and/or power
deposition profiles, a rich variety of transition dynamics is uncover
ed. Transition dynamics and their concomitant thresholds are examined
within the context of these models. In the course of investigating the
se transitions, potential methods for triggering and controlling these
enhanced confinement regimes have been discovered and are discussed.
(C) 1998 American Institute of Physics.