Stellarator Turbulence: Subdominant Eigenmodes and Quasilinear Modeling

Stellarator Turbulence: Subdominant Eigenmodes and Quasilinear Modeling.

Owing to complex geometry, gyrokinetic simulations in stellarator geometry produce large numbers of subdominant unstable and stable, near-orthogonal eigenmodes. Here, results based on the full eigenmode spectrum in stellarator geometry are presented for the first time. In the nonlinear state of a low-magnetic-shear ion-temperature-gradient-driven case, a multitude of these modes are active and ...

Subdominant modes in zonal-flow-regulated turbulence.

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 mode...

Spatial distribution of turbulence in the Wendelstein 7-AS stellarator

In this paper measurements of short wavelength electron density fluctuations using collective scattering of infrared light are presented. The Wendelstein 7-AS (W7-AS) stellarator (Renner H et al 1989 Plasma Phys. Control. Fusion 31 1579) and the diagnostic are briefly described. A series of plasma discharges with reproducible confinement transitions was created by ramping up the plasma current....

Role of stable eigenmodes in saturated local plasma turbulence

The excitation of stable eigenmodes in unstable plasma turbulence, previously documented in collisionless trapped electron mode turbulence, is shown to be a generic behavior of local quasihomogeneous systems. A condition is derived to indicate when such excited eigenmodes achieve a sufficient level in saturation to affect the turbulence, and produce changes in saturation levels, instability dri...

Turbulence Modeling