Electron temperature fluctuations during sawtooth events in a reversed-field pinch

Electron temperature fluctuations are correlated with the dominant (m, n) = (0, 1) edge-resonant magnetic tearing mode during sawtooth events in the Madison Symmetric Torus reversed-field pinch. Electron temperature fluctuations in phase with the (0, 1) tearing mode are measured using highrepetition-rate Thomson scattering. Immediately prior to the sawtooth the (0, 1) island structure appears to be heat-confining, while during the sawtooth it assumes an isothermal character. Core electron temperature variation is also phase correlated with the (0, 1)mode, suggesting that the edge-resonant tearing mode has an effect on core electron thermal confinement during sawtooth events. (Some figures may appear in colour only in the online journal) In standard operation, reversed-field pinch (RFP) tearing modes produce cyclic oscillations (sawteeth) in all macroscopic quantities [1]. Owing to the rapid electron equilibration along field lines, electron temperature measurements provide an excellent tool for deducing the confinement properties associated with tearing mode induced magnetic fluctuations. In the following, high fidelity Thomson scattering (TS) data is used to describe detailed aspects of electron temperature behavior during sawtooth events in the Madison Symmetric Torus (MST) [2] RFP. Recently, electron temperature fluctuations were correlated with the phase of coreresonant, poloidal mode number m = 1 tearing modes and coherent temperature structures were observed in the core of the plasma [3]. However, all m = 1 correlated fluctuations vanish 0.2 ms before the sawtooth and appear again 0.5 ms after the crash. This is the precise time when the edge-localized, m = 0, toroidal mode number n = 1 mode amplitude grows nonlinearly 3 Currently at Pierce College, Lakewood, WA 98498, USA. 0741-3335/11/112001+06$33.00 © 2011 IOP Publishing Ltd Printed in the UK & the USA 1 Plasma Phys. Control. Fusion 53 (2011) 112001 Brief Communication