Investigation of L-H and ITB Transitions in Fusion Plasma Based on Bifurcation Concept

The criteria for the L-H transition and ITB transition in fusion plasmas is studied based on the bifurcation concept. Three transport equations including thermal, particle and toroidal momentum density are solved simultaneously, resulting in the prediction of plasma pressure, plasma density and toroidal velocity profiles at steady state. The thermal and particle transport include both neoclassical and anomalous effects with the velocity shear dependent suppression effect. The results show that the flux (thermal/particle/momentum) versus gradient (pressure/density/velocity) space of each field independently exhibits s-curve bifurcation nature in which a forward L-H and ITB transitions require higher flux than that of the respective backward transitions, hence hysteresis behaviors. In addition, it is found that there exist certain regimes where the transitions are possible. In particular, the ratios of anomalous over neoclassical transport must exceed certain thresholds.