Optical instruments for local divertor observation at wendelstein 7-X

Abstract

The most advanced stellarator at present-Wendelstein 7-X-is currently commissioned. Forschungszentrum Jölich is contributing a number of diagnostic systems in order to participate in the research field of plasma-wall interactions (PWI). The specific interest at Wendelstein 7-X is to study PWI processes in an island divertor with high density and low temperature at steady state. For local characterization of the divertor plasma, a versatile optical observation system is currently developed. The observation of two opposite divertor locations linked by magnetic field lines is aiming at investigating temperature and density profiles, impurities, hydrogen recycling, and transient heat load deposition. The optical systems consist of two mirror based endoscopes each with overlapping fields of view. The light (wavelength range of 350 nm-7000 nm) is divided into ultraviolet, visible and infrared components. Both, cameras equipped with narrow band interference filters as well as spectrometers linked via fibre optics are foreseen. The observation includes photon emission induced by interaction of injected gas (He, N, Ne) with plasma, radiation produced by PWI processes of fuel (H) as well as tomographic reconstruction of the impurity (C, O, N, Ne) radiation in the poloidal sections. Finally, the infrared emission from divertor targets will be recorded at temporal resolution of a millisecond.