Principle of an in-situ relative calibration method using a double-pass beam for Thomson scattering diagnostics

In this paper, we present the detailed principles of an in-situ relative calibration method used to determine electron temperature ( T e ) without using optical relative transmissivity and to obtain the optical relative transmissivity. In this method, a double-pass scattering system is used and ratio between the two signals due to forward and back scattering in each spectral channel is measured. Each signal from both the scattering must be resolved using detectors with a fast response time. Statistical simulation results indicate that the method suppresses the systematic error in T e caused by chromatic degradation in optical components because of the radiation effect. The statistical error is almost the same as that of the standard method, which uses the measured wavelength spectrum to determine the electron temperature and density from a single pass. In this new method, the scattering angle (θ) and T e are considered as important parameters for evaluating its feasibility. Therefore, statistical errors for various θ were investigated. As a result, we found that the method is effective in the range of θ > 105° at T e = 10 keV. The statistical error tends to decrease for high T e measurements.