title: Subdominant modes in zonal-flow-regulated turbulence.
abstract: From numerical solutions of a gyrokinetic model for ion temperature gradient turbulence it is shown that nonlinear coupling is dominated by three-wave interactions that include spectral components of the zonal flow and damped subdominant modes. Zonal flows dissipate very little energy injected by the instability, but facilitate its transfer from the unstable mode to dissipative subdominant modes, in part due to the small frequency sum of such triplets. Although energy is transferred to higher wave numbers, consistent with shearing, a large fraction is transferred to damped subdominant modes within the instability range. This is a new aspect of regulation of turbulence by zonal flows.
authors.affiliation: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: K D
authors.initials: KD
authors.lastname: Makwana
authors.affiliation: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: P W
authors.initials: PW
authors.lastname: Terry
authors.affiliation: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Pueschel
authors.affiliation: Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Hatch