Predicting the Dimits shift through reduced mode tertiary instability analysis in a strongly driven gyrokinetic fluid limit

Abstract

The tertiary instability is believed to be important for governing magnetised plasma turbulence under conditions of strong zonal flow generation, near marginal stability. In this work, we investigate its role for a collisionless strongly driven fluid model, self-consistently derived as a limit of gyrokinetics. It is found that a region of absolute stability above the linear threshold exists, beyond which significant nonlinear transport rapidly develops. While within this range a complex pattern of transient zonal evolution is observed before a stable profile is found, the Dimits transition itself is found to coincide with a tertiary instability threshold so long as linear effects are included. Through a simple and readily extendable procedure tracing its origin to St-Onge 2017 (arXiv:1704.05406) the stabilising effect of the typical zonal profile can be approximated and the accompanying reduced mode estimate is found to be in good agreement with nonlinear simulations.

arXiv comment30 pages, 9 figures; improved the derivation of Appendix A, slightly modified several statements for accuracy, updated figures and notation

References in corpus (15)

• Bifurcation in electrostatic resistive drift wave turbulence
• Multiscale Gyrokinetics for Rotating Tokamak Plasmas: Fluctuations, Transport and Energy Flows
• Critically balanced ion temperature gradient turbulence in fusion plasmas
• Collisionless microinstabilities in stellarators III - the ion-temperature-gradient mode
• Zonally dominated dynamics and Dimits threshold in curvature-driven ITG turbulence
• Theory of the tertiary instability and the Dimits shift from reduced drift-wave models
• Transition to subcritical turbulence in a tokamak plasma
• Drift wave-zonal flow dynamics
• Ion-scale turbulence in MAST: anomalous transport, subcritical transitions, and comparison to BES measurements
• On Nonlocal Energy Transfer via Zonal Flow in the Dimits Shift
• On the Rayleigh--Kuo criterion for the tertiary instability of zonal flows
• Considering Fluctuation Energy as a Measure of Gyrokinetic Turbulence
• Electrostatic stability of electron-positron plasmas in dipole geometry
• Theory of the tertiary instability and the Dimits shift within a scalar model
• Frictionless Zonal Flow Saturation by Vorticity Mixing