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Stacked commercial second generation (2G) high temperature superconducting (HTS) tapes has been demonstrated to have great field trapping ability, with superior mechanical, thermal properties and crossed-field performance to HTS bulks. HTS stacks are considered as a very promising candidate for superconducting permanent magnets, which can be used for many applications like superconducting machines and levitation devices. However, the current magnetization methods for HTS stacks are the conventional magnetization methods developed for HTS bulks decades ago, which have various limitations. On the other hand, the recent progress on HTS flux pumping technology enables HTS coils to be successfully magnetized in an effective and efficient way. In this thesis, these two concepts were combined for the first time. Flux pumping for HTS stacks was proposed and developed as a new magnetization technique. I employed two types of flux pumps, the rotating magnet flux pump and the rectifier type flux pump, to magnetize the modified HTS stacks. The design of the flux pumps, the experimental results and the analysis of the observed behaviours are presented in the thesis. This research provides a new direction in the magnetization of HTS permanent magnets, which has the potential to make HTS permanent magnets more practical with lighter, more compact and efficient magnetization setups.

Both the conditions of the epitaxial growth of YBCO thin films on silicon and the MOS devices operation at 77 K are well known. So, we have defined the technological solutions for the monolithic integration of high temperature superconductor bolometers (YBCO) and amplifiers based on PMOS devices. We have replaced their Al metallization by a Pt/Ti structure. The drain and source contacts were obtained by the preliminary formation of Mo-Si compounds. The YBCO thin film was deposited on silicon using CeO2/Yttria-Stabilized-Zirconia (Y SZ) buffer layers and showed a Tc of 86K. The bolometers and the transistors were successfully tested separetely at 300K and 77K. The co-fabrication on the same silicon substrate of YBCO and PMOS devices is a very promising starting point for a new generation of integrated circuits combining the advantages of the superconductive properties of YBCO and electronics in silicon technolgy.

In the recent years significant progresses in thedevelopment of high-temperature superconductors have been made.It is realistic to believe that power applications, based onthese conductors, in a few years will become available. To beable to utilise the conductors in an optimum way, theunderstanding of their behaviour under application-likecondition is essential. One important parameter that has to beoptimised is the power loss, which means that mathematicalmodels of these losses have to be developed. In a typicalapplication the superconductor is utilised in a coilconfiguration where the actual magnetic field is considerablehigher than for a straight structure. For power frequencies thelosses are dominated by hysteresis losses and flux flowlosses. In this thesis, mathematical models of the hysteresis andthe flux flow losses as a function of a transport current, anexternal magnetic field, the temperature and the frequency havebeen developed. The transport current and the magnetic field,which are assumed to be proportional to each other, includeboth an ac and a dc component. The models of the hysteresislosses are based on the critical state theory, and for twoidealised geometries, an infinite slab and a thin strip, newexact closed form equations have been derived. The equationsfor the two idealised geometries are then superimposed tofacilitate the description of a more realistic geometry, i.e. asuperconducting tape with a finite width and thickness. Themodel of the flux flow losses is valid for a tape shapedconductor and is based on both measurements and reasonablephysical assumptions. For the development and the validation ofthe models, a calorimetric measurement set-up has been used.From a limited number of relatively simple measurements, thedeveloped models can be adjusted to a certain superconductor,and the power losses for the actual superconductor can bepredicted in considerable more complicated cases. <b>Keywords:</b>high-temperature superconductor, hysteresislosses, flux flow losses, critical state model, calorimetricmeasurements

The nonlinear electrodynamic characteristics and presence of vortex dynamics in pseudo 2-dimensional microbridges make them attractive to design novel passive and active microwave circuits. Before such applications could be feasibly accomplished, a greater understanding of the the these devices are necessary, by a complete DC, microwave and optoelectronic characterization. A cryostat design and construction is discussed including the creation of test beds for DC characterization. Coplanar waveguide (CPW) design methodology is presented and used for the creation of CPWs for microwave characterization. Microbridges and meander lines are also embedded into the CPWs for determining the microwave performance of said devices and for optoelectronic characterizations. Results are compared against accepted results from theory and simulations, introducing vortices as explanations for device behaviour. Feasibility of these devices as single photon detectors is discussed.

<p>In the recent years significant progresses in thedevelopment of high-temperature superconductors have been made.It is realistic to believe that power applications, based onthese conductors, in a few years will become available. To beable to utilise the conductors in an optimum way, theunderstanding of their behaviour under application-likecondition is essential. One important parameter that has to beoptimised is the power loss, which means that mathematicalmodels of these losses have to be developed. In a typicalapplication the superconductor is utilised in a coilconfiguration where the actual magnetic field is considerablehigher than for a straight structure. For power frequencies thelosses are dominated by hysteresis losses and flux flowlosses.</p><p>In this thesis, mathematical models of the hysteresis andthe flux flow losses as a function of a transport current, anexternal magnetic field, the temperature and the frequency havebeen developed. The transport current and the magnetic field,which are assumed to be proportional to each other, includeboth an ac and a dc component. The models of the hysteresislosses are based on the critical state theory, and for twoidealised geometries, an infinite slab and a thin strip, newexact closed form equations have been derived. The equationsfor the two idealised geometries are then superimposed tofacilitate the description of a more realistic geometry, i.e. asuperconducting tape with a finite width and thickness. Themodel of the flux flow losses is valid for a tape shapedconductor and is based on both measurements and reasonablephysical assumptions. For the development and the validation ofthe models, a calorimetric measurement set-up has been used.From a limited number of relatively simple measurements, thedeveloped models can be adjusted to a certain superconductor,and the power losses for the actual superconductor can bepredicted in considerable more complicated cases.</p><p><b>Keywords:</b>high-temperature superconductor, hysteresislosses, flux flow losses, critical state model, calorimetricmeasurements</p>

The high-temperature superconductor Sr1-xCaxCuO2 was synthesized using sol-gel, solid-state reaction and co-precipitation methods. The analysis of its formation was made and the structure of the products was determined with the help of the X-ray diffraction. The termal processes, that take place during the synthesis, were analyzed with the help of differential-termal analysis. The experiment has showed that the SrCuO2 formes in the the process of heating the citrats precursors at the temperature of 800oC. And the S0,5Ca0,5CuO2 formes at 900oC by sol-gel, solid-state reaction methods. The best results are achieved using citric gel precursor at the temperature of 900oC. The increase of heating duration up to 36 hours, made no considerable diference in the qualitative composition, however this has changed the quantitative composition.

The nonlinear electrodynamic characteristics and presence of vortex dynamics in pseudo 2-dimensional microbridges make them attractive to design novel passive and active microwave circuits. Before such applications could be feasibly accomplished, a greater understanding of the the these devices are necessary, by a complete DC, microwave and optoelectronic characterization. A cryostat design and construction is discussed including the creation of test beds for DC characterization. Coplanar waveguide (CPW) design methodology is presented and used for the creation of CPWs for microwave characterization. Microbridges and meander lines are also embedded into the CPWs for determining the microwave performance of said devices and for optoelectronic characterizations. Results are compared against accepted results from theory and simulations, introducing vortices as explanations for device behaviour. Feasibility of these devices as single photon detectors is discussed.

This dissertation describes work carried out between June 1987 and October 1991, in the Low Temperature Physics Group at the Cavendish Laboratory, Cambridge. The aim of this work was to use electron tunnelling spectroscopy to measure the density of excitation states of the recently discovered high-temperature superconductors. Tunnelling is the most sensitive method for measuring a superconductor’s energy gap, and historically has provided important evidence for the microscopic mechanism of superconductivity in conventional metals. It was hoped that electron tunnelling would prove equally successful in revealing the mechanism of superconductivity in these new materials. Preliminary experiments showed that a thick, degraded surface layer prevented preparation of high-quality tunnel junctions by conventional evaporation techniques. For this reason, apparatus for the formation and fine control of low-temperature point-contact junctions was constructed, together with new measurement electronics and a computer-controlled data-acquisition system. To test this apparatus, point-contact junctions were formed on conventional superconductors. By increasing pressure of the tip on the sample the junction could be moved from the tunnelling to the metallic regime. Point-contact measurements were then made on a number of ceramic, single-crystal and thin-film high-temperature superconducting materials; some not previously investigated by tunnelling. Although ‘gap-like’ structure was occasionally observed, anomalous features (e.g., voltage-dependent background, broadening, large zero-bias conductance) were always present and usually dominated the tunnelling characteristics. These complicate estimation of the energy gap and preclude measurement of more subtle properties such as gap anisotropy or the effective phonon spectrum, α2F. The origins of these non-ideal features have been much debated in the literature and are reviewed in this dissertation. In the case of thin films deposited by laser ablation the tunnelling characteristics were dominated by single-electron tunnelling effects (Coulomb gap and staircase structure). The results suggest that the surface region consists of numerous, isolated normal metal particles.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21370号 / 工博第4529号 / 新制||工||1705(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 竹内 繁樹, 教授 雨宮 尚之, 准教授 掛谷 一弘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM