Optical Instruments For Local Divertor Observation At Wendelstein 7-X

Abstract

The most advanced stellarator at present -Wendelstein 7-X -is currently commissioned. Forschungszentrum Jülich 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.

Endoscopes for observation of plasma-wall interactions in the divertor of Wendelstein 7-X

“…For this reason, a fast probe manipulator [9] and a poloidal correlation reflectometer [10] have already been developed and installed. A versatile optical observation system [8] in two machine modules located along the same magnetic structure has now been added. Together with two gas inlets installed in the region observed, temperature and density profiles, impurity transport and recycling, hydrogen recycling, and transient heat load deposition can be analysed.…”

“…With a strong focus and background on PWI research at several experiments, together with its preparation by diagnostic development, an experimental program on 'PWI in 3D Plasma Boundary at W7-X' is prepared by developing a dedicated set of diagnostic instruments and modelling activities [6,7]. Newly developed versatile endoscopes [8] for divertor observation being a major tool within this program are described in this paper.…”

Diagnostic set-up and modelling for investigation of synergy between 3D edge physics and plasma-wall interactions on Wendelstein 7-X

“…In order to study the origin of impurities (C is expected to dominate in OP1.2) and edge impurity transport with different magnetic configurations of island divertor on W7-X, a set of endoscopes has been designed for visible and ultraviolet spectroscopy and for tomography of the plasma edge, along with infrared thermography of the divertor tiles [6]. Two of them viewing a lower divertor unit will be available during the OP1.2 phase.…”