Fixed-gradient and fixed-flux full-f simulations of global ion temperature gradient driven turbulent transport

Nakata, Motoki; Idomura, Yasuhiro   

Fixed-flux(FF), fixed-gradient (FG), and local fluxtube (FT) gyrokinetic simulations are systematically compared for ion temperature gradient (ITG) driven turbulence. The plasma size scan in FF simulations show a Bohm like scaling even in a local limit regime, where profile shear effects are weak. It is found that depending on the plasma size and heating power, transient variations of a local power balance in avalanche propagation process produce different levels of super-critical states and burst amplitudes even at similar mean temperature gradients. This mechanism is unique to the FF model, while comparisons of turbulent characteristics in the local limit regime show some similarities among the FF, FG, and FT models. The collisionality dependence of the heat diffusivity is also verified through the comparisons. When the temperature gradient is far from the marginal stability, the FF and FT models give a weak collisionality dependence, while the FG model shows a strong collisionality dependence due to spurious heat sources induced by a relaxation of the plasma distribution towards a collisional equilibrium distribution.