SUPERCONDUCTORS

Author: PÉREZ CABALLERO BELÉN M..
Year: 2003.
University: EXTREMADURA [www.unex.es].
Place of defense: ESCUELA DE INGENIERÍAS INDUSTRIALES.
Place of preparation: ESCUELA DE INGENIERÍAS INDUSTRIALES.

Author: ILIESCU ADRIANA SIMONA.
Year: 2004.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: CENTRO NACIONAL DE MICROELECTRÓNICA BARCELONA.
Place of preparation: ESCUELA DE POSTGRADO.

Summary: The overall objective of this study was to obtain high-temperature superconducting samples of YBCO whose geometries and dimensions exceeding those obtained using techniques of crystal growth. These materials can be integrated into machines eléctirca systems levitaicón or limitations of current. This has promoted research into methods to combine two or more monodominios material superconducting temperature YBCO by a high process soldificación by molten using agetnes soldantes whose melting points are below the melting point of the material you want to join, the YBCO. The first step in obtaining welds high temperature superconducting materials YBCO has been to get an agent soldante appropriate. We have investigated two materials based on metallic silver. Microstructural analysis, along with measures magnetorresistencia and magnetometry Hall has been made in order to find the optimal conditions for achieving high-temperature superconducting weld quality. To understand the process of disseminating the plant in the matrix YBCO has been made unÂ'detallado study of the influence of process parameters of the weld on the microstructure and physical properties of the superconducting unions, ie the magnetization remanenete and the current density criticism generated by this method. It has been shown that these parameters influence both the microstructure and in spropiedades superconducting of artificial joints. To optimize these parameters have been carried out two types of experiments: cooling too fast and slow growth through cooling. Using the cooling experiments have achieved very quickly determine which are the parameters that control the diffusion of silver in the matrix material YBCO. It has been shown that parameters such as time of the cast, the thickness of the sheet metal plant and configuracióne welding are relevant and have been optimized. On the other hand, the influence of parameters such as the cooling rate, maximum temperature process soldadudra and window temperatures in the microstructure of the artificial joints have been analyzed by slow cooling experiments. The influence of these parameters on the superconducting properties of the weld has been studied through measures remnant magnetization of the unions and the equipment YBCO at the same time for comparison. The distribution of the remnant magnetization has been investigated using magnetometry Hall. These measures we hanpermitido deduct the magnitude of the critical current density solving the inverse problem (Bill Biot-Savart). Using the methodology developed in this work we have managed to get artificial joints material YBCO whose microstructures and superconducting properties have a quality similar to those of the starting material YBCO and thus has developed a methodology that will allow superconducting ceramics with larger dimensions and complex shapes .

Author: GONZÁLEZ GONZÁLEZ JUAN CARLOS.
Year: 2004.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: INSTITUT DE CIÈNCIA DE MATERIALS DE BARCELONA.
Place of preparation: ESCUELA DE POSTGRADO.

Summary: Introducing studies not destuctivos made on tapes cuperconductoras and layers of YBCO grown by the technique MOD-TFA through spectroscopy micro-Raman, supplemented by other techniques such as XRD, SEM, TEM, resistivity and critical current density. To quantitatively determine the degree of uniaxial and texture of the bi-axial superconducting tapes of YBCO and investigate issues such as the orientation of the crystal, uniformity, secondary phases, impurities, oxygen content and defects in the layers grown by MOD-TFA based on the rules specific selection for the YBCO and polarized Raman scattering experiments. In addition, we studied the main parameters of growth and its relevance in the final microstructure and superconducting properties. Finally, we study the role of phases intermedidas in the mechanisms of nucleation and growth of YBCO.

Author: CAVALLARO ANDREA.
Year: 2004.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: ICAM-CSIC.
Place of preparation: ESCUELA DE POSTGRADO.

Summary: Tapes of high temperature superconducting (HTS) materials have emerged as promising for their use in the field of energy since l'allow cutting half the size of the teams electricity respect to conventional reduce energy losses, increase the efficiency in the generation, transmission and distribution of the same, and thus reduce the environmental impact. However, variously of drivers typical materials based on oxide superconductors are fragile, and are easily damaged and difficult to process. So far it has been possible to produce a kilometer lengths of the first-generation HTS wire for use in transporting electric current. The superconducting tapes of YBCO, for example, can withstand high critical current density and hence represent a promising candidate in the transport of electricity. One of the substrates available to support the superconductor is a steel with a polycrystalline film epitaxial of YSZ on top, YSZ (IBAD) / Stainless. The second is that we have used the NiO (SOE) / Ni (Rabit), a cienta of nickel previously texturada by rolling and then oxidata in a controlled manner. Many techniques are available for the deposition of YBCO epitaxiale, we choose the cheapest and most industrially interesting: the sol-gel technique. To avoid interaction between the YBCO superconducting and the substrate epitaxial, thus avoiding the reduction of the superconducting current that can transport, it is important to bring an inert material transferring its epitaxial the YBCO; such films are called buffer layers. The main aim of this thesis has been to optimize the growth of the buffer layer by chemical method and finally study the deposition of YBCO by TFA on these samples optimized. The layers of ceramic that we studied were: CeO2, BaZrO3, CaZrO3, CaZrO3, SrZrO3, SrTiO3, BaCeO3 and deposited by the chemical method: metal 2-4-beta-diketone dissolved in acetic acid or metals sisopropoxidos dissolved methanol. By depositing the precursor solutions we used the technique of spin coating. Controlling the various parameters, speed, acceleration and concentration of the solution obtained homogeneous films with varying thickness. The stage of crystallization is achieved in a furnace where it is l'atmosphere, temperature and the speed of heating. During this investigation we have acquired a total increase awareness of thin films of MOD-CeO2. From a combination of TEM analysis, deXRD and RHEED note that the mechanism of growth is anomalous behavior compared to other material grown with the same technique. In this process of synthesis of ceria, homogeneous nucleation in fact this favorite because of the low value of Tnuc. / Tmel ceria (Tnuc. / Tmel = 0.21). Only grains nucleated on the substrate are textured. The dependence of grain size with temperature follows a kind of Arrhenius, characteristics of a growth 3D grain. The analysis EELS showed a significant fraction of residual C adorns the grain boundaries, it is likely to limit the growth of grain remains blocked due to these impurities. A process of annealing in air post, has shown the ability to grow films of CeO2 totally epitaxiales. The analysis EELS such samples treated in oxygen clearly show that the grain boundaries are clean of impurities C, thus unblocking the growth of grain. After a lengthy process optimization parameters summary, we can now control the exact growth epitaxiale of ceria. It has been verified that the cerium oxide can grow in YSZ (IBAD) / SS with only the orientation (001). To preserve the ribbon of metal against oxidation, the process op 8 timizado 6a5 has adapted to the deposition on stainless steel substrate by reducing the temperature synthesis 900Â ° C. We have also optimized the preparation of SrTiO3 (STO) and BaZrO3 (BZO) on MgO and YSZ mono-cristales and then also on YSZ (IBAD) / SS and NiO (SOE) / Ni. The architecture proved to be more promising STO / BZO / NiO (SOE) / Ni. Finally pinning YBCO by TFA method (Trifluoracéticetatos) on the optimized buffer layers. A sample of TFA-YBCO on CeO2/YSZ (IBAD) / SS prepared in air at 900Â ° C in 8 hours has resulted in a critical current density, Jc of 7 MA/cm2 to 5K, and 6.10 5A/cm2 to 77K. These values are close to target one million A/cm2 at 77K. Experiments on buffer layers BZO STO and has shown the ability to use this dual system on NiO (SOE) / Neither alternative as a template for the growth of YBCO. Achieving a critical current density deJc (5K) = 5.10 5A/cm2 with the best shows deYBCO / STO / BZO / NiO (SOE) / Ni.

Author: MENENDEZ NADAL OSCAR.
Year: 2005.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: SALA DE JUNTES-EDIFICI D4-CAMPUS NORD.
Place of preparation: EDIFICI D4 Campus NORD.

Summary: The low losses and high bandwidth of fiber optics have become the means of transmission used in many systems of signal delivery. At present, talk is talk of fiber optic transmission of digital signals. However, applications which are distributed analog signals may also benefit from the transmission characteristics of the optical fibers. These applications include the distribution systems of cable television systems' antenna remote sensing ', mobile communications systems, and so on. Focusing on the uplink for mobile communication systems, the goal is to carry the analog signal picked up by the receiver head up the base station using fiber optics. To perform this transmission technology is used radio over fiber, which consists of a link formed by an electro converter, fiber optics, and a converter opto-eléctrico. The converter performs electro modulation of the optical signal used as a signal modulating the analog signal that one wishes to convey. The fiber-optic links the departure of electro converter with input converter opto-eléctrico, which recovers the analog signal to his departure. The low loss fibers allow, among other things, increase the distance between the head and the base station, allowing, for example, that a large number of cells are controlled by a single base station, and may well reduce both infrastructure as cost of the system. At present, the majority of radio links over fiber using electro converters that perform an intensity modulation of the optical signal, and converters opto-eléctricos engaged in a direct detection of this signal optical modulated intensity. There are two types of electro converters that perform modulation signal strength optics: converters using direct modulation, in which the modulating signal is applied directly to the laser through its current supply to vary the power emitted by optical he and converters using external modulation, in which the laser transmits a constant optical power and modulation is performed on an external device to the laser, which in our case would be a modulator electro Mach-Zehnder. Today, modulators travelling-wave are the most commonly used because its frequency response step under ideal for digital applications. Due to its importance in the market, these modulators are also used for analog applications. However, these applications will see that the use of resonant modulators, whose frequency response is tailored to the response of the analog applications, reduces power requirements regarding modulators travelling-wave. On the other hand, there are receivers heads cooled materials using high temperature superconductors. The low loss of these materials allow significantly increasing the sensitivity and selectivity of the head, allowing, among other things, an increase in the size of the cells with a consequent reduction in the number and / or increase the capacity of the system . Taking into account the former 8 istencia 4db of these receptors heads cooled, both in the study of modulators travelling-wave as resonant modulators use both a driver as a conventional high-temperature superconductors for the metallization of the electrodes. To date, superconducting materials have been used to improve benefits for modulators travelling-wave, but as we will see in this thesis are the resonant modulators which could benefit more of the potential of these materials, as its benefits are highly dependent of losses.

Author: GONZALEZ PARADA ADRIAN.
Year: 2005.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: AULA CAPELLA-ETSEIB.
Place of preparation: COMTE D'URGELL, 187 DESPATX BA17 BARCELONA.

Summary: The development of new technologies of superconductor electrical machines in axial flow configuration has been one of the areas of investigation of DEE of ETSEIB - UPC. In this work a revision becomes of the state-of-the-art of conventional the electrical motors of axial flow and an application in superconductive machines becomes of the same A series of models of motors of axial flow of 4, 6 and 8 poles, was made, designed and constructed with base to the main parameters of the design of this type of machines, that they are the Internal Diameter (Di) and the External Diameter (DO) with a geometry of bilateral stator (the rotor in the middle of two semi-stators), and sets out a new alternative of rotors for this type of motors, in one forms of "flat squirrel cage. A study becomes on rotors of disc of Al, in where different factors are determined that affect the magnetic coupling between the rotor and the stator, as it is the number of The designed stators and rotors are constructed with superconductive tapes of high temperature of composition BSCCO-2223, in where are different aspects from the relation of the critical current of the superconducting one with respect to the number of welded An evaluation becomes of the behaviour of the ferromagnetic material to 300 K and 77 K and tests of their effect in the performance of the motor are made. The evaluations were made on the basis of determining the speed-current relation of each one of the configurations and the characteristics of design for the superconducting motors in configuration of axial flow were determined. The obtained final results in this thesis, which can be used for future designs of electrical machines in configuration of axial flow are: ⢠Application of superconductive tapes HTS in the rotor and the stator ⢠Relation of diameters of the motor ⢠Number of slots/pole in the estator ⢠Optimal number of tape bars HTS in the rotor ⢠Use of ferromagnetic material in the superconducting motor.

Author: RUIBAL ACUÑA MAURICIO.
Year: 2005.
University: SANTIAGO DE COMPOSTELA [www.usc.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FÍSICA.

Summary: In this thesis we studied the mechanism of abrupt jump or 'quenching' that is observed in a superconducting under high current densities applied. Separate without ambigà ¼ age quenching mechanism produced by autocalentamiento other possible mechanisms were measured curves of voltage versus current applied in the millisecond range in micropuentes strains thin YBa2Cu3O7-d with widths below the thermal diffusion length. This condition and obtained using micropuentes with different widths (between 5 and 100 microns) and ramps staggered lasting step of a milisengundo. It was noted that both the resistivity flux-flow as the values of the critical current (which begins gently dissipation) were independent of the width of micropuentes. However, there was a strong dependence of the width and flow of the electric field associated with the abrupt jump. This performance was achieved explain through a mechanism autocalentamiento uniform associated with the movement of flow (flux flow) conveniconal (not unique), without the participation of any other mechanism for quenching. This simulations were performed using in part by finite element numerical calculation. Thus, the mechanism autocalentemiento uniform becomes the mechanism INTRÍNSECO the abrupt transition for this type demonstrate in these experimental conditions.