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The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful operation of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading facilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualification and specification of plasma-facing components, andmore » by modelling codes that simulate edge-plasma conditions and the plasma–material interaction as well as the study of fundamental processes. WP PFC addresses these critical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel) with respect to heat-load capabilities (transient and steady-state heat and particle loads), lifetime estimates (erosion, material mixing and surface morphology), and safety aspects (fuel retention, fuel removal, material migration and dust formation) particularly for quasi-steady-state conditions. Alternative scenarios and concepts (liquid Sn or Li as PFCs) for DEMO are developed and tested in the event that the conventional solution turns out to not be functional. Here, we present an overview of the activities with an emphasis on a few key results: (i) the observed synergistic effects in particle and heat loading of ITER-grade W with the available set of exposition devices on material properties such as roughness, ductility and microstructure; (ii) the progress in understanding of fuel retention, diffusion and outgassing in different W-based materials, including the impact of damage and impurities like N; and (iii), the preferential sputtering of Fe in EUROFER steel providing an in situ W surface and a potential first-wall solution for DEMO.« less

A detailed reaction mechanism is proposed for the formation of crystalline elemental sulfur from aqueous sulfide by oxidation with transition-metal ions like V{sup 5}, Fe{sup 3}, Cu{sup 2}, etc. The first step is the formation of HS{center_dot} radicals by one-electron oxidation of HS{sup {minus}} ions. These radicals exist at pH values near 7 mainly as S{center_dot}{sup {minus}}. Their spontaneous decay results in the formation of the disulfide ion S{sub 2}{sup 2{minus}}. The further oxidation of disulfide either by S{center_dot}{sup {minus}} radicals or by the transition-metal ions yields higher polysulfide ions from which the homocyclic sulfur molecules S{sub 6}, S{sub 7},more » and S{sub 8} are formed. In water these hydrophobic molecules form clusters which grow to droplets of liquid sulfur (sulfur sol). Depending on the composition of the aqueous phase, crystallization of the liquid sulfur as either {alpha}- or {beta}-S{sub 8} is rapid or delayed. Surfactants delay this solidification, while certain cations promote it. All these reactions are proposed to take place in desulfurization plants working by the Stretford, Sulfolin, Lo-Cat, SulFerox, or Bio-SR processes. In addition, the sulfur produced from sulfide by oxidizing sulfur bacteria is formed by the same mechanism, which now explains many observations made previously (including the formation of the byproducts thiosulfate, polythionates, and sulfate).« less

The synthesis of 1,4-((RCp)/sub 2/Ti)/sub 2/Se/sub 4/ R = H (3a), Me (3b), i-Pr (3c) is described together with their applications to the preparation of 1,2,5,6-Se/sub 4/S/sub 4/(4). The deselenization of (RCp)/sub 2/TiSe/sub 5/ (2a-c) with organophosphines gives 3a-c isolated as purple microcrystalline solids. The same compounds could also be prepared from the reaction of (RCp)/sub 2/TiCl/sub 2/ with solutions of Li/sub 2/se/sub 2/. RCp labeling studies show that these Ti/sub 2/Se/sub 4/ compounds do not exchange their (RCp)/sub 2/TiSe/sub 2/ fragments. /sup 77/Se NMR studies indicate that 3c has one type of Se atom while three resonances are observedmore » for the pentaselenide 2c. Compounds 3b crystallizes in the triclinic space group C/anti 1/ with a = 9.577 (2) /angstrom/, b = 15.145 (2) /angstrom/, c = 8.359 (1) /angstrom/, /alpha/ = 97.08 (1)/degree/, /beta/ = 92.02 (1)/degree/, /gamma/ = 89.89 (1)/degree/. A total of 1772 data were processed to a final R/sub F/ = 0.0382, R/sub wF/ = 0.0444. The compound adopts a centrosymmetric chair conformation with Ti-Se and Se-Se distances of 2.55 and 2.34 /angstrom/, respectively. The reaction of 3a and 3b with CS/sub 2/ solutions of S/sub 2/Cl/sub 2/ in a molar ratio 1:2 gave 4 in good yield. The single-crystal X-ray diffraction analysis of 4 indicates the presence of a cyclic crown conformer with the atomic positions occupied statistically by either S or Se due to rotational disorder. Raman spectra show three sets of lines assigned to bond stretching modes /nu//sub Se-Se/, /nu//sub Se-S/, and /nu//sub S-S/. The /sup 77/Se NMR spectrum of 4 exhibits only one line at 651.5 ppm. Upon heating, 4 undergoes two endothermic transformations assigned to polymerization to (Se/sub 2/S/sub 2/)/sub n/ followed by melting at 112.5/degree/C. 28 refs., 4 figs., 5 tabs.« less

Ab initio MO calculations involving the 4-31G* basis set have been used to predict the equilibrium geometries of the hypervalent sulfur hydrides H/sub 2/SS, (HS)/sub 2/SS, H/sub 2/S(SH)/sub 2/, H/sub 2/S(SSH)/sub 2/, and the cyclic H/sub 4/S/sub 4/. The energy changes in their formation from appropriate sulfanes H/sub 2/S/sub n/ (n = 1-4) have been studied with the 6-31G* basis set including the correction for the electron correlation by the second- and third-order Moeller-Plesset perturbation theory. The results are used to discuss the possible pathways in the interconversion reactions between various sulfur compounds containing cumulated SS bonds, for example, themore » formation of S/sub 7/ from S/sub 8/ for which hypervalent intermediates have been proposed recently. Comparison with experimental evidence is made whenever possible.« less