Fast Heat Pulse Propagation by Turbulence Spreading

The propagation of a cold pulse initiated by edge cooling in JET is compared to propagation of the heat wave originating from a modulation of the heating source roughly at mid radius. It is found that the propagation of the cold pulse is by far faster than what could be predicted on the basis of the heat wave propagation, and within local transport models no sufficient explanation for this behaviour can be found. Recently, modelling of the cold pulse propagation using non-local effects and a transport equation that uses fractional derivatives has been successfully applied to model the effect [1]. Here we discuss a model in which the non-locality is introduced by the process of turbulence spreading. Transport models with turbulence spreading have been proposed in [2] and conditions under which the perturbation in the turbulence profile could travel at the required high speed from edge to the core have been established [3]. Here we report on recent results in the modelling of cold pulse propagation using turbulence spreading transport models.