Upgrade of KSTAR MSE with background polychrometers

The 25-sightline Motional Stark Effect (MSE) diagnostic system equipped with the background polychrometer (BP) detectors have been installed to the KSTAR tokamak to simultaneously measure and subtract out the polarized background light in the MSE signals. A series of calibration activities performed for both the conventional (single-detector) MSE and the new MSE-BP systems include the in-vessel absolute polarization angle calibrations, beam-into-gas calibrations, and plasma-sweeping calibrations. Reliable magnetic equilbrium reconstructions with low systematic errors and quantitative estimates on the effect of polarized background noises in the carbon wall are expected from operating both MSE systems. A new real-time MSE data analysis technique under development will be discussed.