Effect of reversed magnetic shear on short wavelength ion temperature gradient modes in ADITYA–U tokamak

Ion temperature gradient (ITG) modes in the short wavelength regime (kθρi >1.0) known as the short wavelength ion temperature gradient (SWITG) modes, are investigated linearly and nonlinearly in the electrostatic limit for ADITYA–U tokamak, in the presence of monotonic and reversed magnetic shear using a global gyrokinetic particle–in–cell (PIC) code, ORB5. It is observed that, while the growth rate of the conventional ITG branch is reduced, the growth rate of the SWITG branch is enhanced by the reversed magnetic shear compared to the case with monotonic shear. The enhancement of the SWITG mode growth rate with reversed shear is attributed to an increase in the contribution from the curvature drift term to the electrostatic field energy. In the nonlinear studies, the zonal shearing rate is found to be reduced by ∼14% in the reversed shear case, as compared to the monotonic shear case. Nevertheless, the overall ion heatflux is reduced by ∼20% as compared to monotonic shear case, which indicates the effectiveness of equilibrium magnetic shearing than nonlinear zonal shear in controlling transport. The contribution from the SWITG branch to the ion heatflux is small, even though it exhibits higher growth rates in the presence of reversed magnetic shear.