Measurements of microturbulence in tokamaks and comparisons with theories of turbulence and anomalous transport

A review of measurements of microscopic fluctuations and theories of turbulence and anomalous transport for tokamaks is given, and some comparisons between theory and experiment are presented. The results of the measurements indicate that all tokamaks have rather similar, broadband, incoherent microscopic fluctuations. Such fluctuations have been measured in the density, potential, electric field, and magnetic field. In the edge regions of three tokamaks, the particle transport caused by the turbulent electric field fluctuations has been measured directly. Although tokamak microturbulence has been studied extensively, neither its source nor its role in anomalous energy transport is yet understood. The incoherent, turbulent nature of the fluctuations has made it difficult to understand them theoretically. Recently, however, significant theoretical progress has been made in several areas including non-linear models of drift wave turbulence and transport, models of anomalous electron thermal conduction by stochastic magnetic field fluctuations, and non-linear models of localized resistive-MHD instabilities. (author)