Optimization of optical filters for ITER edge Thomson scattering diagnostics

In the ITER edge Thomson scattering measurement system, polychromators with optical band-pass filters and avalanche photodiodes are planned to be used. In this paper, we optimized the transmission wavelength ranges of the optical filters by a numerical method. Since measurements in a high electron temperature range are required for the measurement system, the Thomson spectrum could overlap a strong line emission of DαDα when the electron temperature is rather high. It is shown that a filter whose transmission wavelength range is shorter than DαDα becomes important to decrease the measurement error in the high temperature range. Moreover, it is found that a filter whose transmission wavelength range is above 1064 nm (laser wavelength) is useful to improve the measurement accuracy, in particular, when the number of filters is more than six.