Modification of visible spectrometer of Damavand tokamak and study of plasma impurities

Plasma impurities are one of the loss factors of confined energy in tokamaks, so from this regard their study in order to maintain the stability of tokamak plasma and improve the confinement quality is essential. In this research, in order to study the impurities of Damavand tokamak plasma, a monochromator along with a Line Scan CCD array in the assembly of a visible light spectrometer was used. The modified spectrometer system was calibrated by the characteristic wavelengths of a mercury-vapor lamp and was used in the normal plasma regime of Damavand tokamak to record and analyze the radiation in the wavelength range of 3000-7000A°. The finest instrumental resolution of the spectrometer was about 0.9A° at entrance slit width of 50μm, which was used for intensive hydrogen plasma radiation lines such as Hα and Hβ. To study the radiation from the impurities, due to their low intensity, the entrance slit width of 100 μm and the resolution of 1.8A° were selected. The results showed that the predominant impurities in Damavand tokamak plasma are oxygen, nitrogen and carbon, which are generally originated from air molecules trapped in the wall of the vacuum chamber and the plasma facing components, also iron impurities are produced as a result of hot plasma interaction with the limiter and other components inside the vacuum chamber.