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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]

Abstract: A systematic numerical study of the deposition of Be and C atoms on the ITER main chamber first mirrors and their erosion due to fast D(T) atoms has been carried out. The calculations are based on Monte-Carlo neutral transport modelling (with the EIRENE code) on a simulated steady-state plasma background. A generic reduced model of cylindrical and conical diagnostic ducts is considered. The results indicate that the sputtering of the mirrors can be made acceptably small if they are installed in sufficiently long ducts. At the same time the deposition of impurities can be a serious issue even for mirrors protected in long channels. However, the calculations of deposition are not very reliable at the current stage and a need to seriously improve them is indicated. [Copyright &y& Elsevier]

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]

Abstract: The paper presents a review of the development of edge plasma modeling at ITER and of its interaction with the evolving divertor design. The SOLPS (B2-Eirene) code has been developed for, and applied to, the evaluation and the design of the ITER divertor for the last 15 years. With respect to the physics and engineering design, divertor modeling had started as an evaluation tool and has developed into essential design tool synthesizing information from theoretical analysis, experimental studies, and engineering intuition. Examples given in the paper illustrate this process. [Copyright &y& Elsevier]

The CXRS (Charge-eXchange Recombination Spectroscopy) diagnostic for the core plasma of ITER will be designed to provide observation of the dedicated diagnostic beam (DNB) over a wide radial range, roughly from a normalised radius r/a = 0.7 to close to the plasma axis. The collected light will be transported through the Upper Port Plug #3 (UPP3) to a bundle of fibres and ultimately to a set of remote spectrometers. The design is particularly challenging in view of the ITER environment of particle, heat and neutron fluxes, temperature cycles, electromagnetic loads, vibrations, expected material degradation and fatigue, constraints against tritium penetration, integration in the plug and limited opportunities for maintenance. Moreover, a high performance (étendue × transmission, dynamic range) is expected for the port plug system since the beam attenuation is large and the background light omnipresent, especially in terms of bremsstrahlung, line radiation and reflections. The present contribution will give an overview of the current status and activities which deal with the core CXRS system, summarising the investigations which have taken place before entering the actual development and design phase. [ABSTRACT FROM AUTHOR]

Abstract: Laser-based techniques in combination with spectroscopy are proposed for in situ characterization of the first wall in ITER. Three laser-based diagnostics, laser-induced desorption spectroscopy (LIDS), laser-induced ablation spectroscopy (LIAS) and laser-induced breakdown spectroscopy (LIBS) are under investigation in Forschungszentrum Jülich (FZJ) to determine the stored amount of tritium (“tritium retention”) and to characterize the layer deposition on the wall components in fusion devices (thickness, composition, growth rate). Demonstration experiments for LIDS, LIAS and LIBS were performed on TEXTOR and in the laboratory. An advanced ITER prototype version of these diagnostics is currently under preparation on TEXTOR based on coaxial laser beam injection and light detection with the possibility to scan certain wall areas in TEXTOR. It has been demonstrated that LIDS is a reliable diagnostic for the absolute determination of hydrogen isotopes retained on first wall components on the basis of a single laser shot in combination with local Hα spectroscopy. LIAS and LIBS are presently under investigation with respect to their capability to monitor reliably in situ the thickness and composition of deposited layers on the first wall during and between plasma pulses, respectively. A preliminary design and the main parameters for the application of these methods at ITER are discussed. [Copyright &y& Elsevier]

Abstract: The ITER core charge exchange recombination spectroscopy (core CXRS) diagnostic system is designed to provide experimental access to various measurement quantities in the ITER core plasma such as ion densities, temperatures and velocities. The implementation of the approved CXRS diagnostic principle on ITER faces significant challenges: First, a comparatively low CXRS signal intensity is expected, together with a high noise level due to bremsstrahlung, while the requested measurement accuracy and stability for the core CXRS system go far beyond the level commonly achieved in present-day fusion experiments. Second, the lifetime of the first mirror surface is limited due to either erosion by fast particle bombardment or deposition of impurities. Finally, the hostile technical environment on ITER imposes challenging boundary conditions for the diagnostic integration and operation, including high neutron loads, electro-magnetic loads, seismic events and a limited access for maintenance. A brief overview on the R&D and design activities for the core CXRS system is presented here, while the details are described in parallel papers. [Copyright &y& Elsevier]

• 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]