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Erosion from the first mirrors of optical diagnostics can be enhanced by injecting neutral particles into plasma in the vicinity of the diagnostic entrance aperture. In the present paper feasibility of this method for cleaning from deposits is investigated numerically for conditions of the ITER main chamber diagnostics. Besides erosion on the mirror the local gas puff also increases fluxes of impurities due to sputtering from the neighboring surfaces. Calculations have shown that for external impurities coming from the main chamber (Be) the enhancement of erosion – cleaning effect – by far exceeds the extra deposition. However, two further problems have been revealed which may prevent practical use of the proposed technique. First, the gas puffing rate required for effective cleaning may be too large. Second is the contamination by “internal impurities” – sputtered material of the channels where the mirrors are installed. [ABSTRACT FROM AUTHOR]

Optical and laser-based diagnostics in ITER will use mirrors to transmit plasma radiation and laser light to the corresponding detectors and cameras. Mirrors will be sputtered by the fast plasma particles and contaminated by impurities leading to the degradation of the reflectivity and hampering the performance of corresponding diagnostics. Dedicated measures were proposed to minimize the impurity deposition comprising the use of shutters and fins inside diagnostic ducts to trap impurities on their way toward the mirror located in the end of these ducts. Modeling results predict at least 7-fold suppression of the deposition for the duct having four fins located at the distance of a half of a diameter from each other. The Mirror Station (MS) was designed to validate modeling predictions and to study the suppression of deposition inside of diagnostic ducts. The MS contained cylindrical and cone-shaped tubes of different lengths with smooth and shaped geometry of ducts. The MS was exposed in the midplane port of TEXTOR for about 3960 s of plasma operation. After exposure, no drastic suppression of deposition was observed in the cylindrical ducts with fins. In the conical tubes no deposition was detected outlining the advantages of a cone form. [ABSTRACT FROM AUTHOR]

• It is shown that the M1 design based on the use of a thin single-crystal rhodium (ScRh) plate and a special WCu composite is feasible and robust. A rhodium nanocrystalline coating (NcRh) is kept as an optional solution. • The mirror is equipped with an adjustment of 3 DOFs (two rotations and translation) keeping a possibility to recover the initial mirror position without an additional readjustment. • A compatibility with in-situ repetitive cleaning is provided with implementation of the required insulation and gaps. Design option of the RF feeding line connector is presented. • Successful connection between ScRh/WCu samples is achieved. The high quality of the diffusion bonding is confirmed with FIB and metallography examinations, and by mechanical test resulting in the average shear strength of 233.3 MPa. The ITER core charge exchange recombination spectroscopy, which contains five in-port optical mirrors, is intended to transfer the visible light emitted by interaction of the plasma with the diagnostic neutral beam to the corresponding spectrometers. The first mirror (M1) is a key and the most vulnerable component of the diagnostics. In order to provide the required mirror lifetime, maintainability and structural integrity, M1 is composed of special materials, i.e. it is made of a thin 1 mm single-crystal rhodium (ScRh) plate diffusion bonded to a specially matched tungsten-copper substrate. A rhodium nanocrystalline coating (NcRh) can be an option. The paper presents the evolution of the M1 design developed for the optical layout of 2018. M1 is adjustable and cleanable with about 100÷500 procedures of 60 MHz plasma discharge. The mirror design is supported by multifield thermal, electromagnetic and structural analyses and uses experimental data of R&Ds made by Forschungszentrum Juelich, Germany. The study confirms the working capacity of the developed mirror solution. [ABSTRACT FROM AUTHOR]