  The role of magnetic shear for zonal flow generation by
ion-temperature-gradient (ITG-) and trapped electron (TE-) mode turbulence is
studied analytically using fluid descriptions. The scaling of the zonal flow
(ZF) growth rate with magnetic shear is examined and compared with linear
growth rates for typical tokamak parameter values. The results indicate that
large levels of ZF are obtained in regions of negative magnetic shear, in
particular for ZF driven by TE mode turbulence. The strong magnetic shear
scaling obtained for TE mode driven zonal flows originates from the bounce
average of the electron magnetic drifts.

Plasma Physics