Measurement of Faraday rotation in the Implosion Heating Experiment

A technique for measuring Faraday rotation on the Implosion Heating Experiment (a fast 20-cm-radius theta pinch, with n approx. 1015/cm3, B approx. 5 kG) is described. By use of a polarized CO2 laser with a nearly crossed analyzer, the Faraday rotation is measured at one position in the plasma. The nearly crossed analyzer is used to minimize errors due to refraction. The ∫n dl is measured at the same time and radius by using a fractional-fringe interferometer at the He--Ne 633-nm wavelength. From these two measurements the magnetic field is obtained. For comparison the magnetic field is also measured with probes. The results indicate that probes immersed in the plasma are too slow to follow the rapid changes in magnetic field that occur in IHX