MEASUREMENT OF MAGNETIC FLUCTUATION-INDUCED HEAT-TRANSPORT IN TOKAMAKS AND RFP

The local electron energy flux produced by magnetic fluctuations has b een measured directly in the edge plasma (r/a > 0.75) of the Madison s ymmetric torus (MST) reversed field pinch (RFP), continuous current to kamak (CCT), and the scrape-off layer of the TEXT-U tokamak. The Bur p roduced by electrons travelling parallel to a fluctuating magnetic fie ld is obtained from correlation between the fluctuations in the parall el heat flux and the radial magnetic field. The fluctuations in the pa rallel heat flux were measured with a fast insertable pyrobolometer. T he measurements reveal fundamental differences in the nature of electr on energy transport in the RFP and the tokamak. In the RFP the fluctua tion-induced energy flux is large (approximate to 100 kW m(-2), compar able to the total ohmic heating power) inside the reversal surface whe re the magnetic field is expected to be stochastic, and small in the e dge. The magnetic fluctuation induced radial energy flux Q and radial particle flux Gamma (measured independently) are related by a 'convect ive' formula Q approximate to 3/2T Gamma. The electron heat transport is significantly lower than the value predicted by the Rechester-Rosen bluth transport model. This feature of the electron energy transport c an be explained using self-consistent calculations that account for cl umping of electrons streaming along the magnetic field. In the tokamak the magnetic fluctuations do not contribute to the total energy trans port except in the vicinity of the q = 2 magnetic surface, where the t ransport is associated with large amplitude Mirnov oscillations.