It has been shown theoretically that homogeneous kinematic dynamo action is possible for many unconfined and confined velocity fields, but a rigorous experimental validation is still lacking. G. O. Roberts [Philos. Trans. R. Soc. London, Ser. A 266, 535 (1970)] proposed a spatially periodic velocity field capable to generate a dynamo, which Busse [Geophys. J. R. Astron. Soc. 42, 437 (1975)] modified by introducing a second length scale larger in order to obtain a solution for a finite domain. Based on a scale separation approach Busse [Springer Proceedings in Physics, Vol. 69 (Springer Verlag, New York, 1992)] proposed a conceptual design for an experimental homogeneous dynamo. An engineering design was developed and a test facility has been set up. This test facility is described and first experimental results confirming dynamo action are presented.

Plasma-facing materials and components in a fusion reactor are the interface between the plasma and the material part. The operational conditions in this environment are probably the most challenging parameters for any material: high power loads and large particle and neutron fluxes are simultaneously impinging at their surfaces. To realize fusion in a tokamak or stellarator reactor, given the proven geometries and technological solutions, requires an improvement of the thermo-mechanical capabilities of currently available materials. In its first part this article describes the requirements and needs for new, advanced materials for the plasma-facing components. Starting points are capabilities and limitations of tungsten-based alloys and structurally stabilized materials. Furthermore, material requirements from the fusion-specific loading scenarios of a divertor in a water-cooled configuration are described, defining directions for the material development. Finally, safety requirements for a fusion reactor with its specific accident scenarios and their potential environmental impact lead to the definition of inherently passive materials, avoiding release of radioactive material through intrinsic material properties. The second part of this article demonstrates current material development lines answering the fusion-specific requirements for high heat flux materials. New composite materials, in particular fiber-reinforced and laminated structures, as well as mechanically alloyed tungsten materials, allow the extension of the thermo-mechanical operation space towards regions of extreme steady-state and transient loads. Self-passivating

The Karlsruhe Dynamo experiment is aimed at showing that an array of columnar helical vortices in liquid sodium, confined in a cylindrical container, can generate a magnetic field by self-excitation. In three test series it has been demonstrated that magnetic self-excitation occurs and a permanent magnetic saturation field develops which oscillates about a well-defined mean value for fixed flow rates. Dynamo action is observed as an imperfect bifurcation from a seed magnetic field of the environment. Two quasi-dipolar magnetic fields of opposite direction have been realized. A transition between these two states can be enforced through imposition of a sufficiently strong external magnetic perturbation on the existent dynamo field. These perturbations were induced with the aid of two Helmholtz coils. A time series analysis of the magnetic field fluctuations shows several characteristic dynamic features, which are in agreement with theoretical predictions from turbulence models available in the literature.

Today it is generally accepted that the Earth's magnetic field, as well as that of many other planets, is generated by buoyancy driven convection in the electrically conducting liquid cores of these rotating celestial bodies. The conversion of mechanical energy into electromagnetic energy is known as the dynamo effect. In contrast to technical dynamos, which utilize the rotational motion of a complex arrangement of wire coils and other materials of different electrical and magnetic properties, the geodynamo is based on a freely developing spiral flow in a practically homogeneous, electrically conducting liquid core domain, and is therefore termed a homogeneous dynamo. This report outlines some fundamental properties of the Earth's magnetic field. The structure of the spiral flow in the liquid interior of planets is explained with the help of some model experiments in rapidly rotating spherical shells, which were carried out by Busse and Carrigan (1974). Based on the main ideas of electromagnetism it is shown that spiral motion in well-conducting fluids, like liquid metals, can amplify seed magnetic fields to generate dynamo action. Starting from the conjectured flow structure in the Earth's interior, a conceptional and engineering design is described for a laboratory dynamo experiment. Some details of the construction of the test facility and first experimental results are presented and discussed.

The goal of the study was to determine the critical concentrations of Al, Cr and Ni, at which the quaternary Fe-Cr-Al-Ni model alloys, exposed to oxygen-containing molten Pb up to 600°C, are corrosion resistant, while preserving the austenite structure of the alloy matrix. Twelve alloys were designed to meet the above mentioned requirements; six of them showed corrosion resistance and preserved the austenite phase in the alloy bulk, during the exposure at 550°C and 600°C for 1000 hours to molten Pb containing 10-6 wt.% oxygen. Based on experimental results a general formula was substantiated as follows: Fe-(20-29)Ni-(15.2-16.5)Cr-(2.3-4.3)Al (wt.%). In case of temperatures below 550°C, the critical Cr content was 14.4 wt.%. Two corundum-type crystalline structures were identified as the constituent phases of the passivating scales, one being Cr2O3 and the other Al2O3-Cr2O3 solid solution. The average amount of Cr2O3 in the Al2O3-Cr2O3 solid solution, found in the passivating scales of the Fe-Cr-Al-Ni model alloys, was estimated at ≈ 40 wt.% at 550°C and ≈ 35 wt.% at 600°C. A transitional layer, consisting of Fe-and Ni-enriched austenitic matrix and exhibiting randomly distributed intermetallic B2-(Ni,Fe)Al, was formed below the oxide scale up to a depth of two microns. The austenite, as matrix, and Ni3(Al,Fe) as precipitates are the microstructural phases of the bulk alloys after exposure for 1000h at 600°C to oxygen-containing molten Pb.