Design and realization of a sputter deposition system for the \textit{in situ-} and \textit{in operando-}use in polarized neutron reflectometry experiments

We report on the realization of a sputter deposition system for the in situ- and in operando-use in polarized neutron reflectometry experiments. Starting with the scientific requirements, which define the general design considerations, the external limitations and boundaries imposed by the available space at a neutron beamline and by the neutron and vacuum compatibility of the used materials, are assessed. The relevant aspects are then accounted for in the realization of our highly mobile deposition system, which was designed with a focus on a quick and simple installation and removability at the beamline. Apart from the general design, the in-vacuum components, the auxiliary equipment and the remote control via a computer, as well as relevant safety aspects are presented in detail.Comment: Submitted for publication in Nuclear Inst. and Methods in Physics Research, A. (1st revised version

Thermoelectronic Power Generation from Solar Radiation and Heat

Conversion of heat into electric power as done, for example, by fossil-fuel power stations or concentrating-solar power plants, faces the problem that the highest acceptable input temperatures of the converters are usually significantly lower than the temperatures generated by the heat source. Coal, accounting for 40% of global electricity production, is burned at ~1500 °C, whereas the steam turbines to which the combustion heat is delivered are operated below ~700 °C, to give but one example. This temperature gap reduces the maximum conversion efficiency and leads to significant losses. Thermoelectronic generators, which can operate with extremely high temperatures, are compelling candidates to close this gap, boosting the total system efficiency to extraordinary values, yielding a corresponding reduction of emissions. Thermoelectronic generators are based on thermionic energy conversion. Although this technique has been known for more than 100 years, no efficient converters could be built due to the formation of an electronic space-charge region, ruining the performance of practical devices. This thesis presents a solution to the space-charge problem, using electromagnetic fields to convert the space charges into a useful output current. Model calculations, verified experimentally in a prototype apparatus, reveal that there is no fundamental hurdle preventing the development of practical, highly efficient heat-to-electric-power generators. If implemented, these generators could, for example, considerably enhance the efficiency of coal combustion power plants, or operate as highly-efficient solar energy converters.Die Umwandlung von Wärme in elektrische Leistung, wie z.B. in Kohlekraftwerken oder Sonnenwärmekraftwerken, ist der zentrale Prozess der heutigen Stromerzeugung. Dennoch wird der Prozess nicht optimal umgesetzt, da die hohen Temperaturen, die durch die Wärmequellen verfügbar sind, aus technischen Gründen nicht voll nutzbar gemacht werden können. Ein wichtiges Beispiel ist die Kohleverbrennung, durch welche etwa 40 % der Elektrizität weltweit erzeugt werden. Kohle verbrennt bei etwa 1500 °C, wohingegen die Eingangstemperaturen der verwendeten Dampfturbinen unter 700 °C liegen. Dieser Temperaturunterschied vermindert den möglichen Wirkungsgrad und führt zu Energieverlusten. Thermoelektronische Generatoren könnten diese Lücke schließen. Der Wirkungsgrad bestehender Prozesse könnte durch ihren Einsatz erheblich verbessert werden, was mit einer entsprechenden Verminderung der CO2-Emission verbunden wäre. Thermoelektronische Generatoren basieren auf der thermionischen Energieumwandlung. Obwohl die Technik seit über 100 Jahren bekannt ist, ist es bis heute nicht gelungen, das zentrale Problem zu beseitigen: die Ausbildung einer konzentrierten Elektronenraumladungszone im Inneren der Generatoren, welche die Leistung drastisch reduziert. In der vorliegenden Arbeit wird nun eine Lösung für das Raumladungsproblem vorgestellt. Durch einen neuen Ansatz mithilfe elektromagnetischer Felder werden die Raumladungen in einen nützlichen Ausgangsstrom umgewandelt. Modellrechnungen, die in guter Übereinstimmung mit experimentell gewonnenen Daten stehen, zeigen, dass es keinen physikalischen Grund gibt, der die Entwicklung hocheffizienter Generatoren verhindert. Thermoelektronische Generatoren könnten eingesetzt werden, um bestehende Prozesse signifikant zu verbessern, oder direkt als hocheffiziente solar-betriebene Generatoren verwendet werden

Coal phase out, energy efficiency, and electricity imports: Key elements to realize the energy transformation

The energy transformation requires a shift in the energy sector from fossil fuels and their related technologies to carbon free technologies which are mainly renewable energy technologies. In addition to them, three key elements foster the realization of smooth and stringent transformation paths: coal phase out, energy efficiency, and electricity exchange. By applying the techno-economic energy system model REMod-D, the German case is analyzed in this paper with a focus on effects created by emphasizing these three elements in an energy transformation strategy. The analysis covers their impact on the power sector, heating sector, and transport sector which are influenced by the actual shaping of these elements. Overall, the model results show a shift in the German energy system towards a system using more electricity. This electricity is generated up to 85% from photovoltaics, wind power, and other renewable energy sources. Each of the three elements, if employed, leads by itself to a reduction of efforts on the level of developments such as the deployment of renewable energy and renovations, as well as the electrification of vehicles. In the case of combining the three elements, complementary effects can even be summed up. In the Active scenario with a joint use and implementation of the three key elements, this combination is analyzed as part of a cross-sectoral energy strategy for the transformation. Each element can reduce the total system cost by around 16 billion EUR per year. This paper concludes to prioritize these three key elements in the energy strategy in addition to the strong expansion of renewables and the change of heating systems and vehicle concepts