IMPURITY EFFECTS ON DRIFT WAVE STABILITY AND IMPURITY TRANSPORT

A numerical linear stability analysis of electrostatic ion temperature gradient (ITG) and dissipative trapped electron (DTE) modes in a three-component plasma (electrons, primary ions and impurity ions) is performed using a fully kinetic, sheared slab model. The quasi-linear particle and energy fluxes for each species are also computed. For the ITG mode, it is found that increasing plasma dilution (increasing Z(eff)) as well as increasing peakedness of the Z(eff) profile are strongly stabilizing. The quasi-linear calculations of the total anomalous energy flow driven by ITG mode turbulence shows that for Z(eff) profiles that are nearly flat and of moderately low value (Z(eff) less than or similar to 2), an energy 'pinch' is possible. A possible connection of this result with recent DIII-D off-axis heating experiments is discussed. A concomitant feature of this inward energy flow is an inward flow of primary ion particles, and an outward flow of impurity ion particles that greatly exceeds the neoclassical level. The impurity effects on the DTE mode are opposite, i.e. increasing dilution and Z(eff) profile peakedness are strongly destablizing. As a result, quasi-linear theory predicts a large increase in the anomalous electron energy flux and much smaller effects on the anomalous fluxes of the ion species.