Mainz 2022 – scientific programme

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P: Fachverband Plasmaphysik

P 22: Helmholtz Graduate School HEPP V

P 22.2: Talk

Friday, April 1, 2022, 14:25–14:50, P-H12

The importance of the tertiary instability in the collisionless Dimits regime — •Axel Hallenbert and Gabriel Plunk — Max-Planck-Institut für Plasmaphysik, D-17491 Greifswald, Germany

The upshift from the linear instability threshold until turbulent transport commences, caused by self-generated zonal flows, is known as the Dimits shift. Though this phenomenon could facilitate enhanced magnetic confinement device performance, it has proved difficult to understand and quantitatively predict except in simple cases. These have generally been of the simple fluid model kind, so to proceed towards more realistic scenarios, fully gyrokinetic simulations have been used to investigate the Dimits shift in simple geometries. Here the tertiary instabilty, which describes how zonal flows give way to increasing drift waves, was both the main tool and focus. Many features and dynamics previously linked to this instability in fluid models were indeed confirmed to remain in the presence of kinetic effects. Of greatest importance, in the collisionless regime this facilitates an efficient and here accurate Dimits shift prediction, while also hinting at its further validity in more varied geometries.