The radial electric field in a tokamak with reversed magnetic shear

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Abstract
Neoclassical theory with the impurity rotational velocity is used to evaluate the radial electric fleld, Er, in tokamaks. The result of using the complete matrix method for the deuterium-carbon plasma is compared with a reduced analytic formula for deter- mining Er (Ernst et al., (1998)). The analytic formula is shown to overestimate the Er magnitude and its gradient. Two transport measures of the efiect of the Er shear are compared for the reverse shear and enhanced reversed shear discharges in TFTR (Maz- zucato et al., (1996)). We show that the combined Er and magnetic shear measure, ¤s, from linear stability theory gives a higher correlation with the observed transition between the two discharges than the vorticity measure !s from Er shear alone.