Loop voltage anomaly and resistivity profile effects in the Extrap T1 reversed-field pinch

The loop voltage scaling with current in the Extrap T1 reversed-field pinch (RFP) is governed by a strong increase of the anomalous (non-Spitzer) loop voltage which exceeds the decrease of Spitzer voltage with electron temperature. The loop voltage anomaly is discussed in terms of enhanced magneto-hydrodynamic (MHD) dynamo activity, associated with a narrowing of the mean resistivity profile occurring at high current in T1, and potential kinetic losses due to field-aligned, long mean free path electron momentum transfer to the wall. Numerical MHD simulations initiated with various resistivity profiles show a response in current profiles and magnetic fluctuations closely resembling the experimental observations. The results imply that resistivity profile effects may interfere with the intrinsic scaling of the magnetic fluctuation level with the Lundquist number in reversed-field pinches. (author). 13 refs, 3 figs