Laser Faraday rotation measurement of current density fluctuations and electromagnetic torque (invited).

Far-infrared laser polarimetry with time response up to ∼1 μs and spatial resolution ∼8 cm has been successfully implemented on the Madison Symmetric Torus reversed-field pinch. Internal magnetic field and current density fluctuations are nonperturbatively measured. This is accomplished by taking parallel polarimetry chords which measure the line-integrated magnetic field fluctuations via Faraday rotation. With suitable analysis we are able to obtain information on spatial profiles of magnetic field fluctuations and current density fluctuations. Coherent interaction between these fluctuations is also measured and observed to generate an electromagnetic fluctuation-induced torque <δJ×δB>. [ABSTRACT FROM AUTHOR]