Full-F gyrofluid simulation of large-amplitude instabilities, vortices and turbulence*

The standard (“delta-f”) method to split dynamical fields into stationary background profiles and small fluctuations is not applicable to large fluctuation levels, as they for example appear in the edge and scrape-off-layer (SOL) region of magnetized fusion plasmas. “Full-F” gyrokinetic models, which avoid this splitting, are presently developed but pose challenges on computability and costs. Gyrofluid models based on full-F gyrokinetics are much less expensive, but still contain (or may approximately model) relevant physics for edge/SOL turbulent transport. This allows detailed numerical investigations into the basic physics of drift instabilities, vortex dynamics, turbulence and flows in magnetized plasmas, and efficient application to coupled edge/SOL turbulent transport studies in tokamaks and stellarators.

Recent results obtained in our group illuminate the mechanisms of FLR effects on vortex interactions and vorticity dynamics in drift wave turbulence. Large fluctuations and steep pressure gradients have been shown to affect the evolution of zonal flows and geodesic acoustic modes, and cause symmetry breaking in the propagation of SOL blobs and holes. The transition of character from delta-f to full-F turbulence is analysed by 3D and 2D model scenarios and by detailed coupled computations of tokamak edge/SOL electromagnetic drift wave turbulence. The relevance for interpretation of SOL profiles is discussed. Our approach includes self-consistent interaction of (multiple) isotopic or impurity species with plasma edge turbulence. A more exotic fundamental physics application analyses the impact of instabilities and ion impurities on transport in planned magnetized electron-positron plasma experiments.