Design study of polychromators for ITER edge Thomson scattering diagnostics

Kajita, Shin; Hatae, Takaki; Kusama, Yoshinori

In ITER edge Thomson scattering measurement system, it is planned that polychromator by use of optical filters and avalanche photodiodes is 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 low wavelength ranges because high electron temperature measurement is required; therefore, it is important to eliminate the line emission from the plasma. It has been found that a filter below 656 nm, which corresponds to the strong line emission of , is important for evaluating the electron density and temperature because the required maximum temperature is 10 keV, in which the tail of the spectrum is broadened around 400 nm. Moreover, the calculation indicates that a filter, transmission wavelength of which is higher than 1064 nm, is also useful to reduce the measurement error.