Anomalous transport in tokamaks

Abstract

A review is presented of what is known about anomalous transport in tokamaks. It is generally thought that this anomalous transport is the result of fluctuations in various plasma parameters. However, a satisfactory model to explain the origin of the fluctuations has not been identified. The processes responsible for determining the edge energy flux are less clear, but electrostatic convection plays an important part. In the confinement region, experimental observations are presently restricted to measurements of density and potential fluctuations and their correlations. Three distinct features have been identified: the ubiquitous broadband turbulence and a quasi-coherent feature, both of which propagate in the electron diamagnetic drift direction, and an ion feature, which by definition propagates in the ion drift direction. The characteristics of the measured fluctuations have been compared with the predictions of various models. >