The Problem of Marginality in Model Reductions of Turbulence
arXiv:2209.04064 · doi:10.1088/1361-6587/acc276
Abstract
Reduced quasilinear (QL) and nonlinear (gradient-driven) models with scale separations, commonly used to interpret experiments and to forecast turbulent transport levels in magnetised plasmas are tested against nonlinear models without scale separations (flux-driven). Two distinct regimes of turbulence -- either far above threshold or near marginal stability -- are investigated with Boltzmann electrons. The success of reduced models especially hinges on the reproduction of nonlinear fluxes. Good agreement between models is found above threshold whilst reduced models would significantly underpredict fluxes near marginality, overlooking mesoscale flow organisation and turbulence self-advection. Constructive prescriptions whereby to improve reduced models is discussed.
References in corpus (5)
- Tractable flux-driven temperature, density, and rotation profile evolution with the quasilinear gyrokinetic transport model QuaLiKiz
- Transport barrier onset and edge turbulence shortfall in fusion plasmas
- Forcing-dependent stability of steady states in a turbulent swirling flow
- Subcritical turbulence spreading and avalanche birth
- Investigation of a Multiple-Timescale Turbulence-Transport Coupling Method in the Presence of Random Fluctuations