SINGLE CHORD FAR-INFRARED POLARIMETRY EXPERIMENT ON RFX

This paper summarizes the work of the authors in the realization and t esting of a pilot single chord polarimetry experiment on the RFX (reve rsed field experiment) machine; at the far-infrared wavelength of 118. 8 mu m. The fundamental purpose of this experiment is to demonstrate t he feasibility of a Faraday rotation angle measurement on RFX, with th e required resolution, and to clarify all the aspects which may be use ful for the final six-chord version of the diagnostic. The apparatus w hich has been developed is described, with emphasis on some of the mod ifications which proved essential in order to obtain a satisfactory me asurement, in spite of the hostile environment of the machine. Typical results of Faraday angle measurements are presented and discussed, an d the reliability of the measurement is demonstrated. In particular, t he required +/-0.2 degrees accuracy is achieved and the results are co nsistent with magnetic field profiles similar to the ones predicted by the Bessel function model. Suitable design considerations are formula ted in order to guarantee the required performance in the six chord ve rsion, even when the machine moves into full regime. (C) 1995 American Institute of Physics.