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 del 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.