A Self-calibration method for the edge Thomson scattering diagnostic in ITER

Yatsuka, Eiichi; Hatae, Takaki; Kusama, Yoshinori

Calibration of spectral transmissivity of the collection and transmission optics is one of the most crucial issues in Thomson scattering diagnostic system. In ITER, since the vacuum vessel will be radioactivated, it will not be easy to calibrate the spectral transmissivity nearby the vacuum vessel. By injecting additional calibration laser and fitting both of two Thomson scattering lights, one can obtain electron temperature and relative transmissivity of each spectral channel of polychromator from Thomson scattering signal itself. As a calibration laser, Ruby laser is a promissing candidate because wavelength of it is desirable not to differ from both of main laser and lower limit of observation so much. Even when spectral transmissivity is unknown, will be obtained with less than 10 % of accuracy, which is a requirement of edge measurement in ITER.