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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]

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]