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Vacancies in high–purity gold Single crystals have been investigated after quenching from temperatures between 900 and 960°C and after Several steps of an isochronal annealing programme by measurements of the diffuse X–ray scattering intensity close to Bragg reflections, of the lattice parameter change and of the electrical resistivity. From the combined results the volume relaxation of a vacancy was determined to be ΔVrel = − 0·15±0·06 atomic volumes at 5 K. The difference from published values for ΔVrel at high temperatures, that are between — 0·35 and —0·5 atomio volumes suggests a temperature dependence for Vrel in Au. Vacancy clustering is observed at annealing temperatures as low as 0°C, and cluster growth continues right through annealing stage III. The amount of vacancies that agglomerate in clusters (stacking–fault tetrahedra) and the observed decrease in the resistivity per vacancy in the large agglomerates are in reasonable agreement with published results from electron microscope studies.

Delayed elastic phenomenon during high–temperature creep of polycrystalline materials is correlated with strain due to grain boundary sliding. This correlation has been used to develop a phenomenological viscoelastic model that includes the grain–size effect. With ice as a reference material, it is shown that the contribution of the grain-boundary sliding strain to the total strain, and its dependence on stress, time, temperature and grain diameter can be systematically analysed by the proposed model. The results appear to agree with the observed trends in other materials.

The process determining the plasma surface interaction in today's high temperature plasma experiments are investigated following several lines. First, in plasma devices, the particle and energy fluxes to the different first wall areas the fluxes from the walls back into the plasma are measured and the boundary plasma parameters are determined. The surface composition and structure of the walls, limiters and divertor plates are analyzed following exposure to many discharges. Secondly, the different surface processes which are expected to contribute to the plasma surface interaction (particularly to hydrogen particle balance and impurity introduction) are studied in simulation experiments using well defined particle beams.