An investigation of density fluctuations and electron transport in the Madison Symmetric Torus reversed-field pinch

The origin of large scale density fluctuations and their role in electron t ransport has been investigated in the Madison Symmetric Torus reversed-fiel d pinch [R. N. Dexter , Fusion Tech. 19, 131 (1991)]. At medium frequencies (10-30 kHz), (n) over tilde is associated with core-resonant magnetic fluc tuations having poloidal mode number m=1 and toroidal mode numbers n=6-10. These chord-averaged density fluctuations are shown to be coherent with lar ge scale radial flow fluctuations, permitting fluctuation-induced particle flux of the form <(n) over tilde(v) over tilde (r)> to be studied. In the e dge, although amplitudes are large, (n) over tilde and (v) over tilde (r) a re out of phase, consistent with advection of the mean density gradient by perturbed magnetic field lines and no electron transport. During improved c onfinement discharges, produced by inductive current drive, both fluctuatio n amplitudes and the total radial electron flux are greatly reduced over th e entire plasma cross section. (C) 2001 American Institute of Physics.