Laser-induced breakdown spectroscopy (LIBS) is a potential method for in situ monitoring of deposition and retention in fusion devices and is developed with the aim of being integrated in the ...diagnostics system of ITER. The inner divertor of the ITER-like wall of JET was studied by LIBS to show the applicability of the method in JET and ITER. The elemental depth profiles agreed with those given by earlier SIMS measurements. Deuterium was detected in the deposited layers and successfully distinguished from hydrogen. The poloidal patterns of the retained deuterium and deposited beryllium were also in line with the SIMS results with the largest deposition and retention taking place on the top part of Tile 1 and bottom part of Tile 3. The results of these studies support LIBS as a promising in situ solution to replace the present post mortem methods in monitoring metallic deposited layers.
The microstructure changes taking place in W under irradiation are governed by many factors, amongst which C impurities and their interactions with self-interstitial atoms (SIA). In this work, we ...specifically study this effect by conducting a dedicated 2-MeV self-ions irradiation experiment, at room temperature. Samples were irradiated up to 0.02, 0.15 and 1.2 dpa. Transmission electron microscopy (TEM) expectedly revealed a large density of SIA loops at all these doses. Surprisingly, however, the loop number density increased in a non-monotonous manner with the received dose. Performing chemical analysis with secondary ion spectroscopy measurements (SIMS), we find that our samples were likely contaminated by C injection during the irradiation. Employing an object kinetic Monte Carlo (OKMC) model for microstructure evolution, we demonstrate that the C injection is the likely factor explaining the evolution of loops number density. Our findings highlight the importance of the well-known issue of C injection during ion irradiation experiments, and demonstrate how OKMC models can help to rationalize this effect.
Samples with tungsten (W) and tungsten-yttrium (Y) coatings on molybdenum were exposed to plasmas simulating the divertor conditions of ITER. The exposed surfaces were studied using in-situ laser ...induced breakdown spectroscopy diagnostics (LIBS) and the results were compared to those obtained by other surface characterization methods. Our results show that LIBS is a reliable technique for in situ monitoring of erosion, deposition, and fuel retention processes under reactor-relevant conditions. In the regions of the highest gross erosion the thickness of the remaining tungsten layer is thinnest and at the central part of samples both mixing and deposition of components took place. LIBS also allowed reliable recording of D retention. D accumulation is influenced by the surface temperature as well as by the surface irregularities.
Selected Ion Beam Analysis techniques applicable for detecting deuterium and heavier impurities have been used in the post-mortem analyses of tiles removed after the first JET ITER-Like Wall ...(JET-ILW) campaign. Over half of the retained fuel was measured in the divertor region. The highest figures for fuel retention were obtained from regions with the thickest deposited layers, i.e. in the inner divertor on top of tile 1 and on the High Field Gap Closure tile, which resides deep in the plasma scrape-off layer. Least retention was found in the main chamber high erosion regions, i.e. in the mid-plane of Inner Wall Guard Limiter. The fuel retention values found typically varied with deposition layer thicknesses. The reported retention values support the observed decrease in fuel retention obtained with gas balance experiments of JET-ILW.
The aim of this work was to study the applicability of laser induced breakdown spectroscopy (LIBS) as an in situ method for monitoring plasma facing materials in fusion reactors. Tungsten coated ...samples were exposed to Magnum PSI plasma using two different regimes: the steady-state (the sequence of approximately 11s pulses) and the ELM-like. Right after the plasma exposure samples were tested with LIBS in the Magnum PSI analyses and target exchange chamber.
Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the surface morphology and crystallinity. These methods showed that changes at the sample surface caused by used ELM-like mode did not differ remarkably from those caused by steady-state mode. Surface temperature had significant effect on the surface structure. In addition post mortem LIBS measurements were performed that gave result similar to that of in situ LIBS.
Tungsten-coated carbon tiles from a poloidal cross-section of the divertor and several types of erosion–deposition probes from the shadowed areas in the divertor were studied using heavy ion elastic ...recoil detection to obtain quantitative and depth-resolved deposition patterns. Deuterium, beryllium, carbon, nitrogen and oxygen along with tungsten and Inconel components are the main species detected in the studied surface region. The top of Tile 1 in the inner divertor is the main deposition area where the greatest amounts of deposited species are measured. Beryllium and tungsten-containing deposits on the probes (test mirrors and quartz microbalance) indicate that both low-Z and high-Z metals are transported to remote areas. Deposition of nitrogen-15 tracer used for edge cooling only at the end of experimental campaigns in 2012 was also detected giving evidence that nitrogen is effectively retained in wall components.
A set of Be and W tiles removed after the first ITER-like wall campaigns (JET-ILW) from 2011 to 2012 has been analysed. The results indicate that the primary erosion site is in the main chamber (Be) ...as in previous carbon campaigns (JET-C). In particular the limiters tiles near the mid-plane are eroded probably during the limiter phases of discharges. W is found at low concentrations on all plasma-facing surfaces of the vessel indicating deposition via plasma transport initially from the W divertor and from main chamber W-coated tiles; there are also traces of Mo (used as an interlayer for these coatings). Deposited films in the inner divertor have a layered structure, and every layer is dominated by Be with some W and O content.
As a licensed nuclear facility, ITER must limit the in-vessel tritium (T) retention to reduce the risks of potential release during accidents, the inventory limit being set at 1kg. Simulations and ...extrapolations from existing experiments indicate that T-retention in ITER will mainly be driven by co-deposition with beryllium (Be) eroded from the first wall, with co-deposits forming mainly in the divertor region but also possibly on the first wall itself. A pulsed Laser-Induced Desorption (LID) system, called Tritium Monitor, is being designed to locally measure the T-retention in co-deposits forming on the inner divertor baffle of ITER. Regarding tritium removal, the baseline strategy is to perform baking of the plasma-facing components, at 513K for the FW and 623K for the divertor. Both baking and laser desorption rely on the thermal desorption of tritium from the surface, the efficiency of which remains unclear for thick (and possibly impure) co-deposits. This contribution reports on the results of TMAP7 studies of this efficiency for ITER-relevant deposits.
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