The radial electric field in a tokamak with reversed magnetic shear

Neoclassical theory with the impurity rotational velocity is used to evalua te the radial electric field, E-r, in a tokamak. The result of using the co mplete matrix method for the deuterium-carbon plasma is compared with a red uced analytic formula for determining E-r [Ernst et al., Phys. Plasmas 5, 6 65 (1998)]. The analytic formula is shown to overestimate the E-r magnitude and its gradient. Two transport measures of the effect of the E-r shear ar e compared for the reversed shear and enhanced reversed shear discharges in Tokamak Fusion Test Reactor [Mazzucato et al., Phys. Rev. Lett. 77, 3145 ( 1996)]. It is shown that the combined E-r and magnetic shear measure, Y-s, from linear stability theory gives a higher correlation with the observed t ransition between the two discharges than the vorticity measure omega(s) fr om E-r shear alone. (C) 1999 American Institute of Physics. [S1070-664X(99) 03106-7].