Hannover 2020 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 10: Poster Session 2

P 10.15: Poster

Dienstag, 10. März 2020, 16:30–18:30, Empore Lichthof

Towards a Realistic Dimits Shift Prediction using Gyrokinetic Tertiary Instability Calculations — •Axel Hallenbert and Gabriel Plunk — Max-Planck-Institut für Plasmaphysik, Greifswald, Germany

A frequently observed feature in gyrokinetic simulations close to marginal stability is the quenching of transport by persistent, self-generated shearing zonal flows, resulting in a nonlinear upshift of the effective critical gradient known as the Dimits shift. Unfortunately a consistent way to predict the size of the Dimits shift has so far been lacking. In an attempt to remedy this, tertiary instability investigations together with full nonlinear simulations within the Dimits shift regime have been performed for various cases using GENE. Two main conclusions can be drawn, the first of which is that the tertiary instabilities corresponding to the simplified zonal flow profiles previously sufficient to predict the Dimits shift for the Terry-Horton system and the strongly driven gyrofluid limit of gyrokinetics are generally insufficient to explain the Dimits shift in full gyrokinetics. Secondly a further subdivision into two qualitatively different regimes is consistently observed whose separation seems linked with the evolution of the zonal flow profiles in the presence of small-amplitude drift waves.