Optimization of optical filters for ITER edge Thomson scattering diagnostics

Kajita, Shin; Hatae, Takaki; Naito, Osamu

In ITER edge Thomson scattering measurement system, it is planned that polychromators by use of optical band-pass filters and avalanche photodiodes are used for the detection system. In this paper, the optimization of the filter transmission wavelength ranges is performed by minimizing the numerically calculated electron temperature error. The Thomson spectrum extends to considerably short wavelength range because high electron temperature measurement is required; therefore, it is important to eliminate the line emission from the plasma, such as , in particular. It is shown that a filter, the transmission wavelength of which is shorter than , becomes important to decrease the error in high temperature regime. Moreover, when the filter number is more than 7, it is found that a filter, the transmission wavelength of which is higher than the laser wavelength of 1064 nm, is useful to reduce the averaged error in wide temperature range.