AMBIPOLAR MAGNETIC FLUCTUATION-INDUCED HEAT-TRANSPORT IN TOROIDAL DEVICES

The total magnetic fluctuation-induced electron thermal flux has been determined in the Madison Symmetric Torus (MST) reversed-field pinch [ Fusion Technol. 19, 131 (1991)] from the measured correlation of the h eat flux along perturbed fields with the radial component of the pertu rbed field. In the edge region the total flux is convective and intrin sically ambipolar constrained, as evidenced by the magnitude of the th ermal diffusivity, which is well approximated by the product of ion th ermal velocity and the magnetic diffusivity. A self-consistent theory is formulated and shown to reproduce the experimental results, provide d nonlinear charge aggregation in streaming electrons is accounted for in the theory. For general toroidal configurations, it is shown that ambipolar constrained transport applies when remote magnetic fluctuati ons (i.e., global modes resonant at distant rational surfaces) dominat e the flux. Near locations where the dominant modes are resonant, the transport is nonambipolar. This agrees with the radial variation of di ffusivity in MST. Expectations for the tokamak are also discussed. (C) 1996 American Institute of Physics.