Abstract
A laser-based three-wave polarimeter-interferometersystem (POLARIS) is operational on J-TEXT tokamak (R=1.05 m, a=0.27 m) tomeasure plasma electron density and Faraday rotation angle simultaneously.Vibration and collinearity are two key factors which affect the accuracy ofthe measurement. Vibration at the amplitude of even 1 μm is able toinduce almost 1° error (λ=432 μm) to the measurementthrough phase detection. And misalignment of collinearity can also causesystematic error to the measurement of Faraday angle due to density gradientand path length difference. Thus the systematic error from these two sourcesshould be eliminated to obtain accurate equilibrium and fluctuationinformation of the plasma. Some work has been done on optimizing vibrationand collinearity to achieve this goal. After optimization, POLARIS now hasachieved 12 chord measurements (spacing of 3 cm) with high temporal andphase resolution. Details of the optimization and results are described inthis study.
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