Effects of equilibrium-scale radial electric fields on zonal flows and turbulence in helical configurations

Effects of equilibrium-scale radial electric fields ( E r 0 ) on the zonal flow response and the ion temperature gradient (ITG) instability in magnetically confined plasma with helical configurations are investigated by gyrokinetic simulations. Poloidally global simulations of the collisionless zonal flow damping manifest enhancement of the residual amplitude by the uniform and constant E r 0 , and show agreement with the zonal flow response function in the long wavelength limit analytically derived from the theory for helical plasmas with multiple-helicity confinement field components. A higher zonal flow response is found with heavier ion mass for the same ion temperature and E r 0 , that is, the isotope effect, while the ITG mode frequency is Doppler shifted. Accordingly, the isotope dependence of the zonal flow response through E r 0 possibly leads to the ion mass (or the poloidal Mach number) dependence of the turbulent transport and fluctuations.