A possible mechanism for confinement power degradation in the TJ-II stellarator

Abstract

This work uses the outward propagation of spontaneously generated fluctuations of the electron temperature to study heat transport in the TJ-II stellarator. Data from a set of experiments in which the heating power was scanned systematically are analyzed using the transfer entropy. The transfer entropy graph suggests there are at least two modes or channels of propagation: one channel is continuous, reminiscent of diffusion, while the other is non-local, activated mainly when the heating power is large. When the heating power is increased, the region of non-locality expands outwards, leading to the ubiquitously observed deterioration of confinement with heating power.