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- Lagoyannis, A., et al.
(författare)
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Surface composition and structure of divertor tiles following the JET tokamak operation with the ITER-like wall
- 2017
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Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 57:7
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Tidskriftsartikel (refereegranskat)abstract
- Samples extracted from several divertor tiles following the 2011-2012 operation of JET with the ITER-Like wall were analyzed using ion beam analysis methods, x-ray fluorescence spectroscopy, scanning electron microscopy with energy dispersive spectroscopy analysis and x-ray diffraction. The emphasis was on the determination of light species and on material mixing including compound formation on the bottom and the outer divertor tiles. Deposition of deuterium, beryllium, carbon, nitrogen, oxygen, iron, chromium, nickel and molybdenum has been detected on all studied tiles. The thickest deposition, of around 4 mu m, was measured on the bottom of the outer divertor, whereas the other surfaces (inner bottom and vertical outer) the co-deposits were around 1 mu m. x-ray diffraction measurements have revealed the formation of the compound W2C on all specimens.
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- Tsavalas, P., et al.
(författare)
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Fuel retention and carbon deposition on beryllium marker tiles from JET tokamak main chamber limiters investigated by ion beam analysis
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:12
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Tidskriftsartikel (refereegranskat)abstract
- The JET tokamak with the ITER-like wall is operated with arrays of castellated beryllium (Be) limiters in the main chamber. In several locations Be marker tiles were installed for erosion-deposition studies. The castellation sides and the plasma-facing surfaces (PFSs) of Be marker tiles from three different locations of the JET main chamber, from the experimental campaigns 2011-12 (ILW-1) and 2013-14 (ILW-2), were analysed, employing H-2 and He-3 micro-beams in order to determine carbon
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- Kokkoris, M., et al.
(författare)
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Benchmarking the evaluated proton differential cross sections suitable for the EBS analysis of natSi and 16O
- 2017
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 405, s. 50-60
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Tidskriftsartikel (refereegranskat)abstract
- The evaluated proton differential cross sections suitable for the Elastic Backscattering Spectroscopy (EBS) analysis of Si-nat and O-16, as obtained from SigmaCalc 2.0, have been benchmarked over a wide energy and angular range at two different accelerator laboratories, namely at N.C.S.R. 'Demokritos', Athens, Greece and at Ruder Boskovic Institute (RBI), Zagreb, Croatia, using a variety of high-purity thick targets of known stoichiometry. The results are presented in graphical and tabular forms, while the observed discrepancies, as well as, the limits in accuracy of the benchmarking procedure, along with target related effects, are thoroughly discussed and analysed. In the case of oxygen the agreement between simulated and experimental spectra was generally good, while for silicon serious discrepancies were observed above E-p,E-lab = 2.5 MeV, suggesting that a further tuning of the appropriate nuclear model parameters in the evaluated differential cross-section datasets is required.
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- Pinomaa, T., et al.
(författare)
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The significance of spatial length scales and solute segregation in strengthening rapid solidification microstructures of 316L stainless steel
- 2020
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Ingår i: Acta Materialia. - : Acta Materialia Inc. - 1359-6454 .- 1873-2453. ; 184, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser melting (SLM) can produce outstanding mechanical properties in 316L stainless steel. Nonetheless, the technique can lead to considerable variation in quality. This reflects an incomplete understanding and control of the process-structure-properties linkage. This paper demonstrates how length-scale informed micromechanical behavior can be linked to solidification microstructures and how these structures depend on SLM process conditions. This linkage is produced by sequential phase field and crystal plasticity simulations. Rapid solidification is described with a recent quantitative phase field model with solute trapping kinetics, where a range of process conditions are considered in terms of thermal gradients and pulling speeds. The predicted morphological transitions (dendritic-cellular-planar) are consistent with experiments, including segregation-free microstructures, which emerge in planar growth conditions. The predicted cell spacing vs. cooling rate data are also consistent with experiments. The simulated cellular structures produced through phase field modeling are then analyzed with a Cosserat crystal plasticity model with calibrated length-scale and hardening effects and with a solid solution strengthening description that depends on the local microsegregation. It is found that the length scale characteristics and solute segregation greatly influence the overall hardening behavior and affect plastic localization and the evolution of geometrically necessary dislocation (GND) type hardening. Our results suggest that the material strength of SLM 316L steel is more sensitive to cell spacing (microstructural length scale) than to the magnitude of solute segregation. Pulling speed (solidification velocity) is identified as the main process condition determining the material micromechanical behavior. Further analysis of idealized polycrystalline structures demonstrated that plastic incompatibilities and subgrain cell interactions with grain boundaries lead to notable strengthening. The presented sequential phase field-crystal plasticity modeling scheme is a proof-of-concept for systematically investigating and discovering new compositions, process conditions and microstructures for SLM.
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