the phase-modulated signal, and provides a sinusoidal signal at the modulation frequency of 100 KHz whose amplitude is proportional to J,(0m)-Sin(0), where 3m is the amplitude of the modulation angle, 0 is the sum of the rotation angles due to mechanical polarization rotator, 3C, and Faraday rotation in plasma, 3V. Jd^m) is the Bessel function of the first kind with order one. This signal is synchronously detected by a lock-in amplifier, yielding an output voltage, V„ut = V„-Sin (3V). The calibration constant, V,„ can be obtained by setting the mechanical polarization rotator at a few degrees («4°) and measuring the value of V„ut without plasma in the chamber. The system has been employed to study the plasmas in 1SX-B tokamak. Figure 1 shows the time-resolved traces of (a) Faraday rotation and (b) line-averaged electron density, <ne>, of a typical plasma discharge. The position of each channel, relative to the center of the chamber is also indicated in the inset. The negative Faraday rotation on the center channel (channel 2) is due to the outward shift of the plasma center. Data analysis codes have been developed and have been used to reconstruct the asymmetric spatial profiles of electron density and plasma current from the line- averaged chordal measurements. The results are shown in Fig. 2 and are compared with the profiles measured by Thomson scattering. It can be seen in Fig. 2 that two density profiles appear to be in surprisingly good agreement, considering the limited number of channels used in the investigation. The possible reasons for the discrepancy between the current density profiles will be discussed at the symposium, and are currently under investigation. The interferometer/polarimeter system on the TFTR tokamak has been reported5 and the experimental study is under way. Acknowledgements — The authors are greatly indebted to the ISX-B and TFTR groups for their support and cooperation. We also wish to particularly thank E. A. Lazarus for providing the data measured by Thomson scattering. REFERENCES 1. F. DeMarco and S.E. Segre, Plasma Physics 14, 245, 1972. 2. J.H. Vuolo and R.M.O. Galvao, Plasma Physics 25, 1215, 1983. 3. C. Gomez and B. Lax. J. Appl. Phys. 52, 6572, 1981. 4. C.H. Ma, D.P. Hutchinson, P.A. Staats, and K.L. Vander Sluis, Int. J. Infrared Millimeter Waves 3, 263, 1982. 5. D.K. Mansfield, H. Park, L.C. Johnson, and C.H. Ma, Bull. Am. Phys. Sac. 19, 1304, 1984.
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