On resolving the optical spectra of the edge plasma radiation against a strong background of the divertor stray light

A method of detecting a weak radiation of the Balmer lines from the hydrogen isotopes in the edge plasma of a tokamak (SOL) on the strong optical background formed by reflection of the light emitted from the divertor plasma is proposed. The method is based on a parallel registration of the radiation from the optical dump and from the wall near the dump. Calibration of the attenuation of the stray light radiation by the optical dump is being performed in the course of the measurements, using the intensity of the high-frequency pulsations that are not correlated with the edge plasma emission. Statistical estimates show that a 20-fold attenuation of the light by the dump allows registration of the weak edge plasma radiation making down to 0.5% of the background intensity.