Systematic Error Analysis of Thomson Scattering System on VEST With Rotational Raman Calibration

The Thomson scattering (TS) system is a main plasma diagnostic tool used on the Versatile Experiment Spherical Torus (VEST). An upgrade to the 1 kHz TS system has been completed, allowing for the measurement of rapidly changing radial profiles of the electron temperature and density in the core plasma. Additionally, the upgrade of the bandpass filters of the polychromators enables rotational Raman scattering (RRS) calibration, which improves the accuracy of density calibration compared to Rayleigh scattering (RS) methods. However, systematic errors in the relative sensitivity calibration can lead to significant changes in the results. By analyzing discrepancies in the Raman calibration signals for three filters, the causes of these errors are identified and corrected with a fast infrared (IR) LED. As a result, the calibration factors for RRS and their uncertainties are obtained for measuring absolute electron density, and the relative responsivity of each polychromator is corrected to increase the reliability of the TS system.