Effects of radial electric field on zonal flows leading to turbulent transport reduction in fusion plasmas

Turbulent transport in magnetically-confined fusion plasma has been investigated by the use of large-scale gyrokinetic simulations of turbulent transport, where detailed fluctuations of one-body distribution function are directly solved in the five-dimensional phase-space. In fusion plasmas confined by helical magnetic field, an equilibrium-scale radial electric field is formed in association with the neoclassical transport due to binary collisions of particles. Effects of the radial electric field on zonal flows are studied by means of a newly-extended gyrokinetic Vlasov simulation code, GKV. It is found that the poloidal ExB rotation of helically trapped particles enhances the zonal-flow response which may lead to further reduction of the turbulent transport in helical plasmas. The present result supports a new scenario for anomalous transport reduction proposed by a gyrokinetic theory of zonal flows in helical systems. (author)