Full-f gyrokinetic simulations of LOC-SOC transition using GT5D on Fugaku

Idomura, Yasuhiro   

We analyze turbulence transition between linear and saturated Ohmic confinement (LOC-SOC) regimes using the global full-f gyrokinetic simulation code GT5D on the Fugaku supercomputer. The LOC-SOC transition is characterized by the change of intrinsic rotation profiles with a density ramp. This feature is reproduced by numerical experiments, and its mechanism is clarified. The change of collisionality, which depends on the density, induces a transition of dominant micro-instability from trapped electron modes (TEMs) to ion temperature gradient driven modes (ITGs). TEMs and ITGs have different asymmetries in turbulent spectra with respect to the wavenumber in the direction of the magnetic field, leading to the change of momentum transport in the LOC-SOC transition.