Spatio-temporal evolution of the L → H and H → L transitions

Understanding the L → H and H → L transitions is crucial to successful ITER operation. In this paper we present novel theoretical and modelling study results on the spatio-temporal dynamics of the transition. We place a special emphasis on the role of zonal flows and the micro → macro connection between dynamics and the power threshold (P_T) dependences. The model studied evolves five coupled fields in time and one space dimension, in simplified geometry. The content of this paper is (a) the model fundamentals and the space-time evolution during the L → I → H transition, (b) the physics origin of the well-known ∇B-drift asymmetry in P_T, (c) the role of heat avalanches in the intrinsic variability of the L → H transition, (d) the dynamics of the H → L back transition and the physics of hysteresis, (e) conclusion and discussion, with a special emphasis on the implications of transition dynamics for the L → H power threshold scalings.