Remote automatic absolute-polarization calibrations for KSTAR motional Stark effect diagnostic*

The absolute-polarization angle calibration procedure that is conventionally performed inside the vacuum vessel manually has been updated in a remote and automatic manner. It is postulated and experimentally confirmed that the polarized light source does not have to be positioned at the exact intersection between the beam trajectory and the line-of-sight. That is, one can position the linearly polarized light source at any point along the line-of-sight as long as the face of the polarizer is perpendicular to the wave propagation vector. This implicates the calibration hardware including the supporting jig can be installed at a position of convenience and cost-effective. The light source module consists of two motorized rotation stages, one long-distance motorized linear stage, and a two-axis inclinometer sensor. The remote operation is realized by a LabVIEW-based graphical user interface program that also functions automation associated with the KSTAR shot cycle. Precise scans of incident polarization angle with the resolution of down to 1 degree are possible and scans of different polarimeter settings such as photoelastic modulator retardation are performed with the same precision which would never be possible without remote automatic procedures.