EX/P5-3 Momentum Transport from Tearing Instability

In the MST reversed field pinch the radial profile of the plasma rotation undergoes a rapid flattening during magnetic reconnection events. The reconnection events are repetitive (occurring as sawtooth crashes) and correspond to bursts of tearing instabilities. The radial transport of toroidal and poloidal momentum occurs faster than can be explained by collisions. We measure the change in momentum spectroscopically and we measure the fluctuation-induced stresses (Maxwell stresses by laser Faraday rotation and Reynolds stresses in the edge with probes). We find that the stresses are large, but nearly equal in magnitude and opposite in direction, such that their difference can account for the change in momentum. We also report theoretical investigations through quasilinear analytic calculation and nonlinear MHD computation that describe evaluated momentum transport from tearing modes, including their nonlinear coupling. The combined experimental and theoretical studies establish that tearing modes transport momentum, and that the transport is enhanced through nonlinear mode coupling.