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 D(alpha) when the electron temperature is rather high. It is shown that a filter whose transmission wavelength range is shorter than D(alpha) 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. (C) 2009 Elsevier B.V. All rights reserved.