title: Dynamics of zonal flows in helical systems.
abstract: A theory for describing collisionless long-time behavior of zonal flows in helical systems is presented and its validity is verified by gyrokinetic-Vlasov simulation. It is shown that, under the influence of particles trapped in helical ripples, the response of zonal flows to a given source becomes weaker for lower radial wave numbers and deeper helical ripples while a high-level zonal-flow response, which is not affected by helical-ripple-trapped particles, can be maintained for a longer time by reducing their bounce-averaged radial drift velocity. This implies a possibility that helical configurations optimized for reducing neoclassical ripple transport can simultaneously enhance zonal flows which lower anomalous transport.
authors.affiliation: National Institute for Fusion Science, Graduate University for Advanced Studies, Toki 509-5292, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Sugama
authors.forename: T-H
authors.initials: TH
authors.lastname: Watanabe