Perturbative transport experiments have been performed at thestellarator TJ-II. Both the inward propagation of edge cooling pulsesinduced by the injection of nitrogen, and the outward propagation ofheat pulses due to spontaneous spikes of the central temperature havebeen analysed. It has been found that the observed propagation isincompatible with diffusive transport models. Simultaneous inward andoutward propagation eliminates an explanation in terms of a pinch. Anumerical simulation with a resistive interchange turbulence modelsuggests that the observed propagation is related to the successivedestabilizations of pressure gradient driven modes associated withrational surfaces.
New concepts of transport physics in toroidal plasmas