The linear gyrokinetic equation is solved in the local approximation for a
series of advanced stellarator configurations. Included in the model are fi
nite ion and electron temperature gradients and finite plasma beta effects
on general three-dimensional equilibria. This allows investigation of drift
mode instability for core plasma parameters of a helical advanced stellara
tor (Helias) fusion power plant. Numerical results for a Helias reactor con
figuration are presented. It is shown that consistent treatment of beta eff
ects on the geometry is an essential ingredient for microstability calculat
ions.