PI-1 plasma injector with polarimeter laser chord at the 352 position. Laser passes in between inner and outer electrodes.
Three-beam heterodyne polarimeter used at GF.
Polarimeter beam combination and conversion to circular polarization.
Initial beam combination setup gave poorly circularly polarized beams due to difficulties in aligning the beams with respect to the PRRs.
Phase shift responses due to beam polarization ellipticity for different setups. Obtained using λ/2 waveplate rotating at about 15 Hz.
Apparent Faraday rotation during beam alignment by placing a rotating, 14 arc min (0.23°) wedge of ZnSe in the path of the plasma beams. Both signals have bandwidths of 500 Hz. Signal sampled at 10.4 kHz.
Model toroidal field profile along polarimeter chord for shots 34140 and 34704 at the 352 axial position. The electrodes are located at polarimeter chord positions −0.31 m and 0.31 m, and the magnetic axis at 0 m.
Measured Faraday rotation compared to expected Faraday rotation from model toroidal field and density profiles. Signal bandwidths are 5 MHz for polarimeter density and 0.5 MHz for Faraday rotation and surface magnetic field. (a) Shot 34140: Poorly aligned beams produce Faraday rotation measurement that does not agree with model. (b) Shot 34704: Beam alignment error significantly reduced. Faraday rotation measurement agrees well with model.
Spline-fit to surface magnetic probe axial field measurements for shot 34704 at time of peak polarimeter Faraday rotation (488 μs).
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