Tesi: "High critical temperature superconductor"

1

Alméras, Philippe. "Photoemission spectroscopy on high critical temperature superconductors /". [S.l.] : [s.n.], 1995. http://library.epfl.ch/theses/?nr=1334.

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2

Durrell, John H. "Critical current anisotropy in high temperature superconductors". Thesis, University of Cambridge, 2001. https://www.repository.cam.ac.uk/handle/1810/34606.

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After nearly 15 years of research effort, High Temperature Superconductors (HTS) are finding a wide range of practical applications. A clear understanding of the factors controlling the current carrying capacity of these materials is a prerequisite to their successful technological development. The critical current density (Jc) in HTS is directly dependent on the structure and pinning of the Flux Line Lattice (FLL) in these materials. This thesis presents an investigation of the Jc anisotropy in HTS. The use of thin films grown on off c-axis (vicinal) substrates allowed the effect of current directions outside the cuprate planes to be studied. With this experimental geometry Berghuis, et al. (Phys. Rev. Lett. 79,12, pg. 2332) observed a striking flux channelling effect in vicinal YBa2Cu3O7-δ (YBCO) films. By confirming, and extending, this observation, it is demonstrated that this is an intrinsic effect. The results obtained, appear to fit well with the predictions of a field angle dependent cross-over from a three dimensional rectilinear FLL to a kinked lattice of strings and pancakes. The pinning force density for movement of strings inside the cuprate planes is considerably less than that on vortex pancake elements. When the FLL is entirely string-like this reduced pinning leads to the observed channelling minima. It is observed that anti-phase boundaries enhance the Jc in vicinal YBCO films by strongly pinning vortex strings. The effect on the FLL structure cross-over of increasing anisotropy has been elucidated using de-oxygenated vicinal YBCO films. Intriguingly, the counter intuitive prediction that the range of applied field angle for which the kinked lattice is fully developed reduces with increasing anisotropy, appears to be confirmed. Although vortex channelling cannot be observed in c-axis YBCO films, the pinning force density for vortex string channelling has been extracted by observing string dragging. By studying the effect of rotating the applied field at a constant angle to the cuprate planes, it is possible to observe the cross-over into the string pancake regime in c-axis films. In the 3D region, the observed behaviour is well explained by the anisotropic Ginzburg-Landau model. Measurements were also made on thin films of the much more anisotropic Bi 2Sr2CaCu2O8+x material, grown on vicinal substrates. The absence of any flux channelling effect and clear adherence to the expected Kes-Law behaviour in the observed Jc characteristics does not provide evidence for the existence of the predicted 'crossing lattice' in Bi 2Sr2CaCu2O8+x.

3

Jones, Anthony Roger. "Critical currents in granular high temperature superconductors". Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/254043.

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The work described in this thesis consists of an investigation into the behaviour of the critical current density (Jc) of several different high temperature superconductors (HTSCs) as a function of temperature and applied magnetic field. The focus of this research has been to investigate the discrepancies which generally exist between magnetic and transport measurements on HTSCs. In order to do this a number of systems were selected with different weak link strengths, overall alignment and pinning characteristics. Systematic studies were carried out on these systems using both transport and magnetic techniques. The results obtained were compared to obtain a coherent picture of the relation between critical currents in HTSCs, their granularity and structure, and how this accounts for the differences in magnetic and transport measurements. The Jc of granular bulk sintered YBCO was measured as a function of magnetic field and orientation, and attempts made to fit the results obtained to theory. The results obtained indicate that hysteresis of Jc with field cannot be explained by flux trapping alone. Jc measurements were carried out on the 'hub-and-spoke' (H-S) grains of melt-processed YBCO thick films. These indicated that within each H-S grain the current is constrained to radial paths through the centre of the grain. This has major implications for the analysis of any measurements carried out on these samples, as well as for applications, as only a small fraction of the sample carries the applied current. Silver-clad tapes of Tl:1223 and Tl:2223 were measured in different temperatures, applied magnetic fields and orientations. The variation of Jc along the tape length was also measured to provide an estimate of their homogeneity. It was found that the processing route used in the production of these tapes had not aligned the superconductor within them, and also that the tape properties were not homogenous along their length. This probably arises from the crystal structure of the thallium materials. The Jcs of melt-processed thick films of Bi:2212 on silver substrates were measured as a function of temperature and applied magnetic field, and compared with results obtained from magnetic measurements obtained from a VSM. Attempts were made to fit these results to theory. The results obtained show clear scaling behaviour of Jc with T at constant B and imply that the variation in the form of the Jc versus T curves is due simply to the suppression of Tc with increasing applied field.

4

郭明遠 e Ming-yuen Edward Kwok. "Numerical study of an isolated vortex and the lower critical field of a type-II superconductor in the presence of a twin plane". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31213169.

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5

Kwok, Ming-yuen Edward. "Numerical study of an isolated vortex and the lower critical field of a type-II superconductor in the presence of a twin plane /". Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19670151.

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6

Schönborg, Niclas. "Development of loss models for a high-temperature superconducting tape". Doctoral thesis, KTH, Electrical Systems, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3268.

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Abstract (sommario):

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.

Keywords:high-temperature superconductor, hysteresislosses, flux flow losses, critical state model, calorimetricmeasurements

7

Li, Aihua. "A study of the fabrication and characterisation of high temperature superconductor YBa₂Cu₃O₇ thin films". Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20060928.143000/index.html.

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8

McGordon, Andrew. "The current-voltage and noise properties of high temperature superconductor SNS and grain boundary junctions". Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368415.

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9

Putzke, Carsten Matthias. "Fermi surface and quantum critical phenomena of high-temperature superconductors". Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680124.

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This thesis presents the results obtained from de Haas-van Alphen experiments in ironbased superconductors. Measurements of the quasi particle mass in the quantum critical system BaFe2(Asl- xPxh are presented, which show strong enhancement towards the critical composition Xc = 0.3. This is found to be in good agreement with the prediction of a diverging behaviour of the effective mass close to a quantum critical point. Further results obtained on the lower and upper superconducting critical field of this system will be presented, which are found to contradict the expectations from Ginzburg-Landau theory based on results of the quasi particle mass and London penetration depth. However we can reconcile the different experimental findings on superconducting and normal state properties, in this quantum critical system, by considering a significant contribution from Abrikosov vortex core states. The importance of understanding the normal state electronic structure and interactions is shown to be essential for an understanding of the superconducting ground state of a quantum critical system. Further we will show a detailed de Haas-van Alphen study of the il1-type iron-based superconductor LiFeP and its isovalent partner LiFeAs. To understand the formation of nodes on the superconducting gap structure in systems with little change in their Fermi surface topology, is essential for the formulation of a microscopic theory of the pairing mechanism in pnictide-superconductors. 'While we find both systems to be close to the geometric nesting condition, we are able to point to different possible scenarios of the origin of nodes based on quasi particle mass enhancement. Extending the study of quasi particle mass and its relation to the superconducting properties to the stoichiometric high-temperature cuprate superconductor YBa2 CU4 Os, we aim to study the Fermi surface evolution under hydrostatic pressure. As the system has a very stable oxygen stoichiometry which does not allow it to be doped by oxygen ordering, we use hydrostatic pressure to tune the system unexpectedly leading to an increase in the superconducting critical temperature with almost no change to the quasi particle mass .

10

Richens, P. E. "High temperature superconductors in electromagnetic applications". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365792.

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11

Ghazanfari, Nader. "Effects Of Nb2o5 Addition On The Formation And Properties Of Bi-based Superconductors". Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607468/index.pdf.

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Effects of Nb2O5 addition on the formation and properties of the Bi-based superconductors were studied. The superconducting samples were synthesized by two different methods, the solid state reaction (SSR) and ammonium nitrate melt route (ANM) to obtain information about the growth techniques. Ten samples (five with each method) with the chemical compositions of Bi1.6Pb0.4Sr2Ca2Cu3NbxOy, with x= 0.00, 0.05, 0.10, 0.20, and 0.30 were prepared. Phase identification, structural and microstructural analysis were carried out using powder X-ray diffraction method, scanning electron microscopy and energy dispersive X-ray (EDX) analysis. The transition temperature and the critical current measurements were carried out using the electromagnetic measurement system. The critical parameters of the samples were also determined by AC susceptibility and magnetization measurements. Improvements in the formation of the Bi-2223 phase with Nb addition have been observed by both methods. The ANM method leads mixtures of Bi-2223 and Bi-2212 phases, but with the SSR method pure Bi-2223 phase was obtained. With small amounts of Nb addition the critical temperature, Tc, remains the same for ANM samples and it increases for the SSR samples. For both series of samples Tc decreases with further increase of Nb content. With Nb addition the critical currents of the ANM sample almost remain the same and those of the SSR samples increases. Observations based on AC susceptibility measurements showed that Nb addition improve inter-grain coupling. Inductive critical current densities obtained from magnetization measurements agree with the critical currents stated above and show that Jc increase with increase Nb content.

12

Lalonde, Richard. "Flux line interactions in conventional and high critical transition temperature superconductors". Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/6031.

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We have developed a novel experimental approach for the study of the interaction of sheets of non parallel flux lines in hysteric type II superconductors. We continuously monitor the evolution of the components of the magnetic flux density $\Vert$ and $\perp$ to $H\sb{a}$ (i.e. $\langle B\sb{z}\rangle$ and $\langle B\sb{y}\rangle$) as $H\sb{a}$ is raised to various intensities, and then reduced to zero. In our investigation of a high $T\sb{c}(YBa\sb{2}Cu\sb{3}O\sb{7-x}$) ceramic, $H\sb{a}$ exceeded $H\sb{*}$, the first full penetration field. We applied the phenomenological Clem general critical state model to the analysis of our extensive observations. A computer program was developed to solve the four coupled differential equations of this theory with appropriate physical constraints for the situations prevailing in our experiment. This analysis provides detailed insight into the evolution of the intricate configurations of the magnetic flux density $\vec B$(x), the critical current density, $\vec J$(x), and electric field $\vec E$(x) patterns as the injected and trapped flux lines are made to interact, unpin, migrate and undergo flux cutting processes. The model is seen to generate the variety of complicated measured curves of $\langle B\sb{y}\rangle$ and $\langle B\sb{z}\rangle$ vs $H\sb{a}$ very satisfactorily. (Abstract shortened by UMI.)

13

McDowell, John Christopher. "Preparation characterisation and stability of selected high critical temperature ceramic superconductors". Thesis, University of Ulster, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260854.

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14

Yang, Yifeng. "Studies on aspects of the critical current in high temperature superconductors". Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315086.

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15

Everett, John. "Dissipation in high temperature superconducting tapes". Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8576.

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16

Xu, Ming. "Critical current density and time-dependent magnetization of the high transition temperature superconductors". Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/30033.

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17

Shin, Jae-Kyoung. "Mechanical Behavior and Its Relation to Superconducting Property of High Temperature Composite Superconductors". 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/66211.

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Abstract (sommario):

Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第14163号
工博第2997号
新制||工||1445(附属図書館)
26469
UT51-2008-N480
京都大学大学院工学研究科材料工学専攻
(主査)教授落合庄治郎, 教授河合潤, 准教授奥田浩司
学位規則第4条第1項該当

18

Gandolfini, Germain. "Comparison of flux line cutting behaviour in high critical temperature and conventional Type II superconductors". Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5757.

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The magnetic behaviour (magnetization curves, Meissner effect, hysteresis losses, remanent flux and flux line cutting) for high $T\sb{c}$ samples of Nd and $YBa\sb{2}Cu\sb{3}O\sb{7-x}$ at 77 K, semi-reversible PbIn and hysteretic VTi at 4.2 K have been investigated and compared. The magnetic behaviour of the high $T\sb{c}$ samples and of the PbIn are remarkably similar but contrasts dramatically with the phenomena observed in the VTi. A hump structure appears in the low field region of the initial magnetization of the high $T\sb{c}$ samples. This phenomenon occurs because the sintered samples consist of a compact agglomeration of small irregularly shaped grains which are electrically coupled before the hump structure but are isolated after this feature. We show that the appropriate calibration should be based on the diamagnetic response of the uncoupled grains. A large ratio of $j\sb{c\Vert}$ to $j\sb{c\perp}$ (the critical current densities $\Vert$ and $\perp$ to the flux line density) accounts for the observations on the VTi in the flux cutting regime whereas $j\sb{c\Vert} \approx j\sb{c\perp}$ is indicated by the behaviour of the high $T\sb{c}$ and PbIn samples.

19

Hamid, Hamidi A. "The effect of strain and temperature on the critical current density of high-field superconductors". Thesis, Durham University, 1997. http://etheses.dur.ac.uk/5078/.

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A J(B,ϵ) probe has been designed and built to measure the critical current density, J(_c), versus strain on short superconducting wires and tapes. Measurements can be made from 2K to 4.2K in high magnetic fields in our 17T magnet system and at 77K for strains up to ±1.0%.The effect of strain on J(_c) has been measured on a 0.37mm diameter Nb(_3)Sn wire at 4.2K and 2.9K from l0T up to 14T. The compressive pre-strain of the wire measured at 4.2K is found to be about 0.3%. At 4.2K, the value of B(_c2) maximum is 19.6T and at 2.9K is 21.2T. The functional form of the flux pinning of the sample at 4.2K can be expressed as F(_p)=4.20±0.57xl0(^8)[B(_c2)(ϵ)](^1.67±0.7b(^1/2)(l-b)(^2); and for the sample at 2.9K it is F(_p)=1.37±0.05xl0(^10)[B(_c2)(ϵ)](^0.54±0.16b(^1/2)(l-b)(^2). From temperature scaling, the functional form is F(_p)=3.63 ±0.62xl0(^8)[B(_c2)(T)](^1.72±1.3)b(^1/2)(l-b)(^2). The difference in the values of n between strain scaling and temperature scaling shows that n only parameterises the change in J(_c) with change in strain or temperature. The effect of strain on J(_c) has been measured on five short sections of an Ag-sheathed BSCCO(2223) tape at 4.2K and in magnetic fields up to 12T. J(_c) degradation starts to occur between 0.18%-0.25% strain. The appearance of secondary peaks in the critical current distribution is attributed to inter-grain J(_c) and infra-grain J(_c). J(_c) measurements have been made on bulk PbMo(_6)S(_8)(PMS) samples. J(_c) increased by a factor of «7 when the sample was hot isostatically pressed(HIP). Measurements have also been made on series of HIP'ed gadolinium(Gd) doped Pbi(_1-x)Gd(_x)Mo(_6)S(_8) samples. The highest T(_c) value is 14.55K when x=0.1. The highest J(_c) is when x=0.2. The irreversibility field B(_irr)(0) from J(_c) measurements has been calculated to be 53.9T, 45.5T, 34.IT and 33.5T for the x=0, 0.1,0.2 and 0.3 samples, respectively.

20

Ciceron, Jérémie. "Superconducting magnetic energy storage with second-generation high temperature superconductors". Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAT012/document.

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En chargeant en courant une inductance supraconductrice, on stock de l’énergie magnétique. Ce principe est appelé SMES pour Superconducting Magnetic Energy Storage. Ce type de dispositifs a une densité d’énergie relativement faible mais peut avoir une densité de puissance élevée. Cette thèse s’inscrit dans le cadre du projet BOSSE, qui vise à mettre au point un démonstrateur de SMES dans la gamme du MJ. Ce SMES sera à la fois plus compacte que ses prédécesseurs et battra le record actuel d’énergie spécifique d’un bobinage supraconducteur en atteignant 20 kJ/kg. Cet objectif sera atteint grâce à l’utilisation de supraconducteurs haute température critique de seconde génération, dits conducteurs « REBCO ».Cette thèse aborde de manière générale la problématique du design de SMES et propose des éléments de réflexion et des solutions pour un pré-design rapide du bobinage d’un SMES. Le design du SMES à haute densité d’énergie du projet BOSSE est détaillé.Des éléments modulaires (galettes de ruban REBCO) du SMES ont été fabriqués et testés en champ propre et sous champ magnétique externe. Les méthodes et les résultats de détection de transition des galettes de l’état supraconducteur vers l’état normal sont présentés. Ces détections ont permis de garantir l’intégrité des galettes REBCO lors de transitions, même à très forte densité de courant (980 A/mm2 dans le conducteur nu).Ce travail est soutenu par la DGA (Direction Générale de l’Armement)
Magnetic energy is stored when a superconducting inductance is fed with current. This principle is called SMES (Superconducting Magnetic Energy Storage). This kind of device has a relatively low energy density but can have a high power density. This PhD work has been conducted in the frame of the BOSSE project with the objective to develop a SMES demonstrator in the MJ range. This SMES will be especially compact and will reach a specific energy of 20 kJ/kg of winding, which is 50 % over the current world record for a superconducting coil. This performance is made possible by the use of 2nd generation high critical temperature superconductors, so-called “REBCO” conductors.This work tackles the general problematic of SMES design and proposes elements of reflection and solutions for fast pre-design of a SMES winding. The design of the high specific energy SMES of the BOSSE project is presented in detail.Modular elements (pancakes of REBCO tapes) of the SMES have been manufactured and tested in self-field and under background magnetic field. During these tests, transitions from superconducting state to normal state have been detected. These early detections have prevented the pancakes to be damaged when transitions occurred, even at very high current density (980 A/mm2 in the bare conductor). The measurement method is presented, as well as the results of the tests.The BOSSE project has been funded by the DGA (French Defence Procurement Agency)

21

Pei, Ruilin. "Measurement and analysis of critical current and AC loss of HTS tapes in a superconducting machine". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609019.

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22

López, Bermúdez Juan Santiago [Verfasser]. "Correlation between Critical Magnetic Fields and Carrier Distance in High Temperature Superconductors / Juan Santiago López Bermúdez". München : Verlag Dr. Hut, 2014. http://d-nb.info/1058285432/34.

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23

Espinosa, Arronte Beatriz. "Resistivity and the solid-to-liquid transition in high-temperature superconductors". Doctoral thesis, KTH, Microelectronics and Applied Physics, MAP, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4251.

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Abstract (sommario):

In high-temperature superconductors a large region of the magnetic phase diagram is occupied by a vortex phase that displays a number of exciting phenomena. At low temperatures, vortices form a truly superconducting solid phase which at high temperatures turns into a dissipative vortex liquid. The character of the transition between these two phases depends on the amount and type of disorder present in the system. For weak point disorder the vortex solid-to-liquid transition is a first-order melting. In the presence of strong point disorder the solid is thought to be a vortex-glass and the transition into the liquid is instead of second order. When the disorder is correlated, like twin boundaries or artificially introduced columnar defects, the transition is also second order, but has essentially different properties. In this work, the transition between the solid and liquid phases of the vortex state has been studied by resistive transport measurements in mainly YBa2Cu3O7-[delta](YBCO) single crystals with different types of disorder.

The vortex-glass transition has been investigated in an extended model for the vortex-liquid resistivity close to the transition that takes into account both the temperature and magnetic field dependence of the transition line. The resistivity of samples with different properties was measured with various contact configurations at several magnetic fields and analyzed within this model. For each sample, attempts were made to scale the transition curves to one curve according to a suitable scaling variable predicted by the model. Good scaling was found in a number of different situations. The influence of increasing anisotropy and angular dependence of the magnetic field in the model were also considered.

The vortex solid-to-liquid transition was also studied in heavy-ion irradiated YBCO single crystals. The ions create columnar defects in the sample that act as correlated disorder. A magnetic field was applied at a tilt angle with respect to the direction of the columns. At the transition the resistance disappears as a power law with different exponents in the three orthogonal directions considered. This provides evidence for a new type of critical behavior with fully anisotropic critical scaling properties not previously found in any physical system.

The effect on the vortex solid-to-liquid transition of high magnetic fields applied parallel to the superconducting layers of underdoped YBCO single crystals was also studied. Some novel features were observed: a sharp kink appearing close to Tc at high magnetic fields and a triple dip in the angular dependence of the resistivity close to B||ab in some regions of the phase diagram.

I högtemperatursupraledare består en stor del av det magnetiska fasdiagrammet av en vortexfas som uppvisar ett flertal spännande fenomen. Vid låga temperaturer bildar vortexarna en fast vortexfas utan elektriskt motstånd. Vid högre temperatur övergår denna fas till en dissipativ vortexvätska. Egenskaperna hos denna fasövergång beror på oordningen i form av defekter. Vid svag punktoordning är fasomvandlingen mellan det fasta och flytande vortextillståndet en första ordningens smältövergång. Vid stark punktoordning anses den fasta fasen vara ett vortexglas och övergången till vortexvätskan är istället av andra ordningen. När oordningen är korrelerad, som för tvillinggränser eller artificiellt skapade kolumndefekter, är övergången också av andra ordningen men med väsentligt annorlunda egenskaper. I detta arbete har övergången mellan det fasta och det flytande vortextillståndet studerats med resistiva transportmätningar i framförallt enkristaller av YBa2Cu3O7-[delta] (YBCO) med olika typer av oordning.

Vortexglasövergången har undersökts i en utvidgad modell för resistansen i vortexvätskan nära fasövergången där hänsyn tas till såväl temperatur- som fältberoendet. Resistansen hos prover med olika egenskaper mättes i varierande magnetfält och i flera kontaktkonfigurationer och analyserades inom denna modell. Övergångskurvorna skalades till en kurva med en skalningsvariabel som givits av modellen. God skalning uppnåddes i flera olika fall. Effekten av ökande anisotropi och vinkelberoendet i modellen undersöktes också.

Vortexövergången mellan det fasta och det flytande vortextillståndet undersöktes även i enkristaller av YBCO bestrålade med tunga joner. Jonerna skapade kolumndefekter som fungerar som korrelerad oordning. Vinkeln mellan pålagt magnetfält och dessa kolumndefekter varierades. Vid fasövergången avtar resistansen som en potenslag med olika exponenter i de tre undersökta ortogonala riktningarna. Detta ger experimentell belägg för en ny typ av kritiskt beteende med fullständigt anisotropa kritiska skalningsegenskaper.

Egenskaparna hos på vortexövergången mellan fast och flytande fas vid höga magnetfält parallella med de supraledande lagren hos underdopade YBCO enkristaller undersöktes också. Några nya effekter observerades: en skarp knyck uppstod nära Tc vid höga magnetfält och en tredubbel dipp i den vinkelberoende resistiviteten nära B||ab i några regioner av fasdiagrammet.

24

Al-Mosawi, Maitham Khazal. "The fabrication and characterisation of High Temperature Superconducting tapes and coils". Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287318.

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25

Nyhus, Jørgen. "Resonant Ultrasonic System Design, and Measurements of Critical Behaviour and Flux-Line Elasticity in High Temperature Superconductors". Doctoral thesis, Norwegian University of Science and Technology, Department of Physics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-2117.

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26

Testa, Joseph Anthony. "Experimental studies of 1/f noise in high-critical-temperature superconductors in the normal and superconducting states /". The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487587604133792.

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27

Friend, Christopher Michael. "Transport critical current density measurements on high and low temperature superconductors in magnetic fields up to 15 tesla". Thesis, Durham University, 1994. http://etheses.dur.ac.uk/5827/.

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A probe for measuring the transport critical current density (J(_c)(B,T)) of superconductors has been constructed, extending the magnetic field and temperature range of previous probes. It can measure critical currents up to 500A, from 2K up to 150K, inside the bore of a 17T Tesla magnet. The temperature is held constant during measurement to: ±50mK at 4.2K and below; ±70mK at 20K; ±100mK at 80K and ±200mK at 150K. The J(_c)(B,T) of a Nb(46.5wt%)Ti multifilamentary wire has been measured in transverse and longitudinal fields. The longitudinal orientation has both a higher J(_c) and upper critical field. It is found that the orientation, field and temperature dependence of J(_c)(B,T) is described by a single functional form. In particular, the orientation dependence determined only by the upper critical field, the anisotropy of which is due to variations in the microstructure or flux cutting events. A Bi(_2)Sr(_2)Ca(_2)Cu(_3)O(_x) tape has been measured in three different orientations. An anomaly in J(_c) is observed, only below 10K, at a field B(_2)(T) for each orientation. Above IT the data are best described by the function J(_c)(B,T)=a(_j)(T)exp{-B/β(T)}. There is a crossover to a stronger field and temperature dependence of J(_c) at temperatures above 55K. Close to the irreversibility line there is a markedly different field dependence of J(_c) depending on whether the field is perpendicular or parallel to the tape surface. A new description has been put forward to explain the data. It is suggested that the intergrain material of the tape is a low Tc BSCCO phase, possibly die 2201 or 2011 phase, of which B,(T) is die upper critical field. Above 10K, in fields less than IT, J(_c) is determined by coupling across S-N-S Josephson junctions at the grain boundaries. Above IT, current mainly flows between grains by connections which allow it to remain in the crystal ab-planes. J(_c)(B,T) is then determined by intrinsic properties and follows the exponential functional form. This form is determined by die average field component parallel to the c-axis. It is proposed that collective pinning theory offers the best framework for describing J(_c), in which case the crossover could be due to a pinning phase transition. The J(_c)(B,T) of some Bi(_2)Sr(_2)Ca(_1)Cu(_2)O(_x), multifilamentary wires is explained using the same description of S-N-S coupling and ab-plane connections as for the 2223-tape. However, whereas the tape was highly aligned throughout, each wire filament has aligned grains in the region of die BSCCO-Ag interface but an untextured core. It is in the aligned regions of each filament that most of die ab-plane connections exist. Increasing the number of filaments therefore improves the wire performance in high fields, though phase purity and density are still important. The 19 and 37 filament wires are promising for high field applications below 20K. The results on the BiSrCaCuO tape and wires demonstrate that, in this material, J(_c)(B,T) can be improved with better texturing and connectivity between grains. To advance the theory a better understanding of die average pinning potentials in BSCCO is required.

28

Milliken, Damion Alexander. "Uranium doping of silver sheathed bismuth-strontium-calcium-copper-oxide superconducting tapes for increased critical current density through enhanced flux pinning". Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20040810.154223/index.html.

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29

Saleh, Paul Matthew. "Characterisation of practical high temperature superconductors in pulsed magnetic fields and development of associated technology". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365786.

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30

Yuan, Weijia. "Second-generation high-temperature superconducting coils and their applications for energy storage". Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/229754.

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Since a superconductor has no resistance below a certain temperature and can therefore save a large amount of energy dissipated, it is a 'green' material by saving energy loss and hence reducing carbon emissions. Recently the massive manufacture of high-temperature superconducting (HTS) materials has enabled superconductivity to become a preferred candidate to help generation and transportation of cleaner energy. One of the most promising applications of superconductors is Superconducting Magnetic Energy Storage (SMES) systems, which are becoming the enabling engine for improving the capacity, efficiency, and reliability of the electric system. SMES systems store energy in the magnetic field created by the flow of direct current in a superconducting coil. SMES systems have many advantages compared to other energy storage systems: high cyclic efficiency, fast response time, deep discharge and recharge ability, and a good balance between power density and energy density. Based on these advantages, SMES systems will play an indispensable role in improving power qualities, integrating renewable energy sources and energizing transportation systems. This thesis describes an intensive study of superconducting pancake coils wound using second-generation(2G) HTS materials and their application in SMES systems. The specific contribution of this thesis includes an innovative design of the SMES system, an easily calculated, but theoretically advanced numerical model to analyse the system, extensive experiments to validate the design and model, and a complete demonstration experiment of the prototype SMES system. This thesis begins with literature review which includes the introduction of the background theory of superconductivity and development of SMES systems. Following the literature review is the theoretical work. A prototype SMES system design, which provides the maximum stored energy for a particular length of conductors, has been investigated. Furthermore, a new numerical model, which can predict all necessary operation parameters, including the critical current and AC losses of the system, is presented. This model has been extended to analyse superconducting coils in different situations as well. To validate the theoretical design and model, several superconducting coils, which are essential parts of the prototype SMES system, together with an experimental measurement set-up have been built. The coils have been energized to test their energy storage capability. The operation parameters including the critical current and AC losses have been measured. The results are consistent with the theoretical predictions. Finally the control system is developed and studied. A power electronics control circuit of the prototype SMES system has been designed and simulated. This control circuit can energize or discharge the SMES system dynamically and robustly. During a voltage sag compensation experiment, this SMES prototype monitored the power system and successfully compensated the voltage sag when required. By investigating the process of building a complete system from the initial design to the final experiment, the concept of a prototype SMES system using newly available 2G HTS tapes was validated. This prototype SMES system is the first step towards the implementation of future indsutrial SMES systems with bigger capacities, and the knowledge obtained through this research provides a comprehensive overview of the design of complete SMES systems.

31

Ghorbani, Shaban Reza. "Structural and Electrical Transport Properties of Doped Nd-123 Superconductors". Doctoral thesis, KTH, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3461.

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It is generally believed that one of the key parameterscontrolling the normal state and superconducting properties ofhigh temperature superconductors is the charge carrierconcentrationpin the CuO₂planes.By changing the non-isovalent dopingconcentration on the RE site as well as the oxygen content in(RE)Ba₂Cu₃O_7−δ, an excellent tool is obtained tovary the hole concentration over a wide range from theunderdoped up to the overdoped regime.In the present thesis thefocus is on the doping effects on the structural and normalstate electrical properties in Nd-123 doped with Ca, La, Pr,Ca-Pr, and Ca-Th.T he effects of doping have been investigatedby X-ray and neutron powder diffraction, and by measurements ofthe resistivity, thermoelectric powerS, and Hall coefficient R_H.T he thermoelectric power is a powerful tool forstudies of high temperature superconductivity and is highlysensitive to details of the electronic band structure.Sas a function of temperature has been analyzed in twodifferent two band models.The parameters of these models arerelated to charactristic features of the electron bands and asemiempirical physical description of the doping dependence ofSis obtained.So me important results are following:

(i)The valence of Pr in the RE-123 family.Results from thestructural investigations, the critical temperature Tc, and thethermoelectric power indicated a valence +4 at low dopingconcentration, which is in agreement with results of chargeneutral doping in the RE-123 family.(ii)Hole localization. The results of bond valence sum (BVS)calculations from neutron diffraction data showed that holelocalization on the Pr⁺⁴site was the main reason for the decrease of thehole concentration p.Differ ent types of localization wereinferred by S measurements for Ca-Th and Ca-Pr dopings.(iii)Competition between added charge and disorder. Theresults of RH measurements indicated that Ca doping introduceddisorder in the CuO₂planes in addition to added charge.This could bethe main reason for the observed small decrease of thebandwidth of the density of states in the description of aphenomenological narrow band model.(iv) Empirical parabolic relation between γ and p.S data were analyzed and well described by a two-band modelwith an additional linear T term, γT.An empiricalparabolic relation for γ as a function of holeconcentration has been found.

Key words:high temperature superconductors, criticaltemperature, resistivity, thermoelectric power, Hallcoefficient, X-ray diffraction, Neutron diffraction, NdBa₂Cu₃O_7−δ, hole concentration,substitution.

32

Lanckbeen, Alain. "Study of physico-chemical and physical properties of the high critical temperature superconductor YBa2Cu3O7-d in relation to the substitution of copper by zinc or iron and the oxygen stoichiometry". Doctoral thesis, Universite Libre de Bruxelles, 1994. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212699.

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33

Duncan, Fiona Hazel. "Characterisation of superconducting Nd123 solid solutions and related phases". Thesis, University of Aberdeen, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297558.

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The stoichiometry of the Nd_1+xBa_2-xCu₃O_7-δ solid solution has been investigated using XRD and EPMA. At 980°C in air, an essentially continuous solid solution forms with limiting compositions x_min = 0.03(1) and x_max = 0.92(2). The solid solution limits are independent of temperature over the range 300 to 1050°C, i.e. stoichiometric Nd123 does not form. Preliminary studies show that annealing in an Ar atmosphere does not affect x_min. Three structurally distinct polymorphs of Nd123ss exist - tetragonal Nd123ss, orthorhombic Nd123ss and orthorhombic Nd123ss. The stability range of each in air has been determined. Quenched samples with 0.03 ≤ x ≤ 0.6 have the tetragonal Nd123ss structure. On oxygenation, samples with 0.03 ≤ x <0.2 are orthorhombic. The orthorhombic-tetragonal phase transition is second order, both with increasing temperature and increasing x. Samples with 0.7-0.9 have the orthorhombic Nd213ss structure at all oxygen contents. Tetragonal Nd123ss is isostructural with tetragonal Y123 and orthorhombic Nd123ss is isostructural with orthorhombic Y123. Orthorhombic Nd213ss has the ideal stoichiometry Nd₂BaCu₃O_7-δ and is based on a 2a x b x 2c superstructure of the Nd123ss structure. The supercell is due to ordering of the Nd and Ba atoms, which leads to ordering of the oxygen atoms. Melting temperatures decrease with x. Two distinct regions of melting behaviour are observed; the first for 0.03 ≤ x ≤ 0.6 with a thermal minimum at x0.4, and the second for 0.7 ≤ x ≤ 0.9. Oxygen contents increase with x. Samples with larger x values have a smaller range of oxygen contents. High pressure oxygen annealing results in a constant Cu valence state of 2.35 for all values of x. Average copper valence states <2 are only obtained readily for x ≤ 0.3. T_c decreases with x and samples become non-superconducting at x0.5. For samples annealed in 1 bar O₂, 'double plateau' behaviour is observed.

34

Iliescu, Adriana Simona. "Superconducting joints of melt-textured YBCO monoliths: preparation, microstructure and critical currents". Doctoral thesis, Universitat Autònoma de Barcelona, 2004. http://hdl.handle.net/10803/3359.

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El objetivo general de este trabajo ha sido el de obtener muestras superconductoras de alta temperatura de YBCO cuyas geometrías y dimensiones superen a las obtenidas mediante técnicas de crecimiento cristalino. Estos materiales pueden ser integrados en maquinaria eléctrica, sistemas de levitación o limitadores de corriente. Este objetivo ha promovido la investigación hacia métodos que permiten unir dos o más monodominios del material superconductor de alta temperatura YBCO mediante un proceso de solidificación por fundido utilizando agentes soldantes cuyos puntos de fusión están por debajo del punto de fusión del material que se quiere unir, el YBCO
El primer paso en obtener soldaduras superconductoras de alta temperatura del material YBCO ha sido el de conseguir un agente soldante apropiado. Hemos investigado dos materiales basados en plata como agentes soldantes: polvo de óxido de plata y una lamina de plata metálica. Análisis microestructural, junto con medidas de magnetorresistencia y magnetometria Hall se han realizado con el fin de encontrar las condiciones óptimas para conseguir soldaduras superconductoras de alta temperatura de alta calidad.
Para entender el proceso de difusión de la plata en la matriz YBCO, se ha realizado un detallado estudio de la influencia de los parámetros del proceso de la soldadura en la microestructura y las propiedades físicas de las uniones superconductoras, es decir la magnetización remanente y la densidad de corriente critica, generadas mediante este método. Se ha demostrado que estos parámetros influyen tanto en la microestructura como en las propiedades superconductoras de las uniones artificiales. Para optimizar estos parámetros se han realizado dos tipos de experimentos: enfriamiento muy rápido y crecimiento mediante enfriamiento lento. Utilizando los experimentos de enfriamiento muy rápido hemos conseguido determinar cuales son los parámetros que controlan la difusión de la plata en la matriz del material YBCO. Se ha demostrado que parámetros como: tiempo del fundido, el grosor de la lámina de plata y la configuración de la soldadura son relevenates y han sido optimizados. Por otro lado, la influencia de parámetros como: la velocidad de enfriamiento, temperatura máxima del proceso de la soldadura y la ventana de temperaturas en la microestructura de las uniones artificiales se han analizado mediante experimentos de enfriamiento lento.
La influencia de estos parámetros en las propiedades superconductoras de las soldaduras se ha estudiado a través de medidas de magnetización remanente de las uniones y del material YBCO, a la vez para su comparación. La distribución de la magnetización remanente ha sido investigada utilizando magnetometria Hall. Estas medidas nos han permitido deducir la magnitud de la densidad de corriente crítica resolviendo el problema inverso (ley Biot-Savart).
Utilizando la metodología desarrollada en este trabajo hemos conseguido obtener uniones artificiales del material YBCO cuyas microestructuras y propiedades superconductoras tienen una calidad similar a las del material inicial YBCO y por lo tanto se ha desarrollado una metodología que permitirá obtener ceramicas superconductoras con dimensiones mayores y formas complejas.
The final goal of this PhD thesis was to obtain YBa2Cu3O7- (YBCO) samples with different geometries and bigger dimensions than those obtained by the crystalline growth techniques. These materials can be integrated in electrical machinery, levitating devices or fault current limiter systems. This need has driven the investigation to welding techniques that can joint two or more YBa2Cu3O7- single-domains by a solidification process using welding agents whose melting points are below the melting point of YBa2Cu3O7- material.
The first step in achieving high temperature superconducting YBCO joints was to find a suitable welding material. We have investigated two Ag based materials as welding agents: Ag2O powder and Ag thin foil. Microstructural analysis along with magnetoresistance and in-field Hall mapping measurements have been performed to find the conditions to reach a high quality superconducting joints.
A deep study of the influence of different parameters on the microstructure and on the superconducting properties of the final joints, i.e. remanent magnetization and critical current density of the final joints, generated using a YBCO/Ag/YBCO architecture has been performed in order to understand the role of the Ag diffusion and to optimize the welding process. It has been shown that these parameters influence in one way or another the microstructure and superconducting properties of the final joints. In order to optimize these parameters, we have performed two kinds of experiments: quench experiments and slow cooling experiments. By quench experiments we have succeed in controlling the Ag diffusion process into the YBCO matrix. Parameters such as: melting time, Ag foil thickness and weld configuration have been investigated and optimized. On the other hand, the influence of parameters such as: cooling rate, processing temperature and window temperature, on the microstructure of the final joints has been analyzed by slow cooling experiments.
The influence of welding parameters on the superconducting properties of the final joints has been studied by determining the remanent magnetization profiles of each sample and calculating from them the critical current density of the joints and YBCO grains for comparison. The remanent magnetization distribution on samples joint by the welding process was investigated by using a Hall probe imaging system. These measurements allowed us to deduce the magnitude of the critical current densities by solving the inverse problem, as well as the homogeneity and spatial scale on which they flow.
We have proposed a methodology in order to determine the critical current density from the results obtained after solving the inverse problem. We have observed that the current distribution pattern obtained from this methodology agrees well with current distribution profile predicted by Bean model.
In summary, by employing the new welding methodology developed in the present work, we have been able to obtain YBCO superconducting joints having a clean and crystallographic coincident microstructure and with critical current densities through the joint similar to those of the YBCO monoliths.

35

Sneary, Adrian Bernard. "The fabrication of a high temperature superconducting magnet and critical current characterisation of the component Bi₂Sr₂Ca₂Cu₃Oₓ tapes and filaments in high magnetic fields". Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4517/.

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The transport critical current density (J(_c)) of a 37 filament Bi-2223/Ag tape has been measured as a function of field and temperature from 4.2 K up to 90 K. Data have been obtained over a large current range from 10 mA up to 100 A and in fields up to 23 T with the tape in 3 orientations with respect to field. These comprehensive data have been used to test the predictions of the flux creep and weak link models used to explain J(_c) in Bi-2223 tapes. The J(_c)(B,T) dependence of optimised Bi-2223 tapes has been calculated using a curved film model. The model assumes perfect grain connectivity and that the local superconducting properties are equivalent to those in the best reported thin films. A comparison between the calculations and measured J(_c)(B,T) dependencies suggest that in high fields at 20 K, J(_c) in presently available industrially processed tapes is only a factor of 8 below the performance of ideal fully optimised tapes. Transport measurements have been made on Bi-2223 single filaments extracted from an alloy sheathed multifilamentary tape in liquid nitrogen at 77 K in fields up to 300 mT with the field aligned parallel and perpendicular to the a-b planes. Further Jc(B,T) data have been taken in a variable temperature insert at temperatures between 60 to 90 K in fields up to 15 T. In a study of the electric field-current density {E-J) characteristics of the c-axis orientated data at 77 K, negative curvature is observed in traces below 280 mT. However, the 280 mT trace exhibits both positive and negative curvature in different current regimes in contrast to the predictions of standard theory. A laboratory scale Bi-2223 superconducting magnet producing a maximum field of 1.29 T at 4.2 K has been designed and fabricated. The magnet comprises 6 resin impregnated double wound pancakes with a 40 mm bore fabricated via the react and wind route. Critical current density measurements have been made as a function of magnetic field, angle and strain at 4.2 K and 77 K on short samples of the constituent tape. The E-J characteristics of all component coils have been measured and a comparison with short sample data shows that minimal additional damage occurred beyond that produced by the bending strain on the tape and the long length variation in J(_c). Sufficient detail is provided for the non-specialist to assess the potential use of brittle superconducting tapes for magnet technology and construct a laboratory scale magnet.

36

Keys, Simon Alastair. "Temperature and strain scaling laws for the critical current density in Nb(_3)Sn and Nb(_3)Al conductors in high magnetic fields". Thesis, Durham University, 2001. http://etheses.dur.ac.uk/3951/.

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Detailed, accurate measurements of critical current density and resistivity to determine the upper critical field have been made on a technological NbsAl conductor in magnetic fields up to 15 T, temperatures from 4.2 K up to the critical temperature and in the strain range from -1.8% to 0.7%. The uncertainty in temperature above 4.2 K was equivalent to ± 100 mK with a stability during the measurements of < 5 mK up to a limiting current of 80 A and a typical noise level of 1 µ Vm(^-1).When B(_c2){T,ε) is defined at 5%pn, 50%pn or 95%/%pn, an empirical relation is found where and an approximate relation, holds. The Jε data were parameterised using F(_p) = J(_E)B = A(ε)[Bc(_2)](^n)b(^p)(1-b)(^9) where b = B/B(_c2)(T,ε). When B(_c2)(T,ε) is constrained to be the value at 50%pn or 95%pn, the scaling law for F(_p) breaks down such that p and q are strong functions of temperature and q is also a strong function of strain. However, when B(_c2)(T,ε) is defined at 5%pn, there is good scaling where p and q are constants independent of temperature and strain. F(_p) can also be approximated by a Kramer form where the Ginzburg-Landau constant is γ is the electronic density of states and is interpreted as the average B(_c2) for the bulk where percolative current flow occurs. The critical current density of Hot Isostatic Pressed (HIP'ed) and unHIP'ed Nb(_3)Sn Modified Jelly Roll wires has also been measured at 4.2 K. The critical current and upper critical field were decreased for the HIP'ed sample. The reduced upper critical field of the HIP'ed wire was found to be less sensitive to strain than the unHIP'ed wire. The exponent of B(_c2) in the flux pinning scaling law increased from 0.86 to 2.14 as a result of the HIP processing.

37

Chouial, Baghdadi. "Investigation of superconductor tunnel junctions on YBCO high temperature superconductor". Thesis, University of Bath, 1991. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303029.

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38

Severac, Childerick Henri Louis. "Spin injection into high temperature superconductor". Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369295.

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39

Huang, Taotao. "Quench modelling of high temperature superconductor". Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/65717/.

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HTS magnets have been developed to generate high magnetic fields because its high critical field at low temperatures. For HTS magnets, the design of thermal stability and protection is based on understanding of its quench behaviour. However, there are few experimental and numerical results on the quench behaviour of HTS at low temperatures. This thesis work is mainly dedicated to investigate the quench behaviour of high temperature superconductor (HTS) at low temperatures by 1D and 2D numerical analysis. In addition, this work also investigates the critical current of HTS coils made from Bi/Ag2223 tape at 77K under self-field. The ANSYS implementation of a general quench model capable of handling nonlinear heat generation over a large temperature range of current sharing, e.g. for HTS at low temperatures, has been successfully validated for HTS at high temperatures and LTS with reference to predictions by the classical quench theory. The numerical model also revealed that the classical theory usually overestimates the minimum quench energy MQE as self-heating is neglected during the development of MPZ. The effective medium approximation for the coil thermal-electrical properties was also found to be sufficient for practical HTS coils. Simulation of 1D HTS conductors at low temperatures using the non-linear heat generation model revealed a different quench behaviour from that of LTS conductors. Firstly, while the minimum quench energy MQE is well defined, it is almost an order of magnitude smaller than the enthalpy of the minimum propagation zone. Hence the growth of MPZ is entirely due to self-heating while MQE is just a sufficient trigger. Secondly, for a practically defined MQE with 95% of the ”true” minimum, there is a large variation of the size of MPZ and the corresponding quench temperature. Thirdly, there appears a simple scaling between the average MPZ heat generation Gq and the temperature range (Tq − Tcs) of MPZ. 2D analysis of HTS coils showed the MQE is an order of magnitude larger than that from 1D analysis because of radial heat conduction. For practical coils, the geometry ii and boundary cooling have an important influence on their quench behaviour while the MPZs are larger and hotter. Two single pancake coils of 50mm inner diameter and 20 turns were manufactured and tested at 77K. The current carrying characteristics of HTS coils was evaluated by using the method based on the Ic-B of bifilar tape and agree well with measured results. One bifilar pancake coil was fabricated and tested at 77K. The measured critical current is 108A and about 20% larger than that of a single pancake coil.

40

McDonald, Peter Hughes 1965. "High temperature superconductor thin film optical detectors". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277167.

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Since the recent discovery of a new class of high critical temperature superconductors (HTS), much interest has been shown in their potential use as optical detectors. The purpose of this research was to test thin film samples of the HTS Y1Ba2Cu3O7-delta as detectors and investigate any response to optical radiation. A laboratory test facility was designed and built for this purpose. The experimental results exhibit a variety of optical responses that are dependent upon the physical characteristics of each HTS thin film. Polycrystalline films exhibited a different detection mode than did epitaxial films. This research demonstrates that HTS thin films are viable optical detectors and have the potential to become competitive high-performance detectors as the new technology continues to emerge.

41

Lecrevisse, Thibault. "Contribution à l'étude des aimants supraconducteurs utilisant des matériaux supraconducteurs à haute température de transition". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00875176.

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L'apparition ces dernières années de supraconducteurs réalisés industriellement utilisant des composés à haute température de transition offre la possibilité de nouveaux développements en magnétisme supraconducteur. En effet ils permettent d'augmenter le champ magnétique généré en conservant une cryogénie classique à 4,2K d'une part, et ils ouvrent la voie à des développements d'aimants supraconducteurs fonctionnant entre 10 et 30K d'autre part. Les matériaux supraconducteurs à haute température critique sont alors indispensables pour dépasser les inductions magnétiques de 16 T (cas de l'insert dipolaire HTc pour le Large Hadron Collider du CERN) ou augmenter la densité spécifique d'énergie stockée dans un SMES (Superconducting Magnetic Energy Storage, cas du projet ANR SuperSMES).Les atouts incontestables (température critique, champ magnétique critique, résistance mécanique) apportés par l'utilisation des matériaux supraconducteurs à haute température critique tels que l'YBaCuO dans les aimants supraconducteurs demandent de relever quelques défis. Leur comportement est encore mal compris, surtout lors des transitions résistives. Arriver à protéger ces conducteurs requiert une réflexion nouvelle sur les systèmes de protection destinés à éviter les dégradations thermiques et mécaniques. La réponse à la question " peut-on utiliser ces matériaux de manière pérenne dans les aimants supraconducteurs ? " est incontournable.Des éléments de réponse sont donnés ici. L'utilisation des conducteurs est abordée à travers différentes études expérimentales permettant de mieux connaître le conducteur (caractérisation électrique et modélisation de la surface critique) d'une part et de définir les étapes clés de la fabrication des aimants supraconducteurs à haute température de transition (étude des jonctions entre conducteurs ou entre galettes) d'autre part. Cette étude a abouti à la réalisation de deux prototypes d'aimants ayant permis d'identifier les difficultés liées à l'utilisation des rubans d'YBaCuO. Un modèle thermoélectrique des supraconducteurs à haute température de transition est développé et un code numérique basé sur le logiciel de calcul par Eléments Finis CASTEM permet d'étudier le phénomène de transition résistive, ou quench, dans un conducteur et dans un aimant. Le code a été validé sur des essais réalisés au Laboratoire National des Champs Magnétiques Intenses de Grenoble. Les résultats obtenus ont permis la définition des conducteurs pour les deux projets liés à la thèse et la validation de la protection.

42

Dorget, Rémi. "Étude et conception d'une machine supraconductrice à modulation de flux pour application aéronautique". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0018.

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Dans le cadre de la lutte contre le changement climatique, l'industrie aéronautique s'est fixé pour objectif la neutralité carbone totale en 2050. Pour cela, l'emploi de technologies de rupture est nécéssaire pour réduire les émissions de ce secteur en forte croissance. Parmi ces technologies, on retrouve l'électrification mais dont le déploiement nécessite de disposer de machines électriques à forte puissance spécifique. Dans ce contexte la supraconductivité peut être une voie d'amélioration pour les machines électriques grâce aux fortes densités de courant ainsi qu'aux champs magnétiques intenses qu'il est possible de générer avec les matériaux supraconducteurs. L'inconvénient principal de cette technologie est la nécessité de fonctionner à des températures cryogéniques. Cependant, la perspective de l'emploi par les avions de l'hydrogène liquide comme carburant, transporté à -253 °C, présente une synergie avec la supraconductivité. C'est dans ce cadre que se placent les travaux de cette thèse qui a pour but d'étudier l'utilisation des matériaux supraconducteurs à haute température critique pour le développement d'un moteur supraconducteur à haute puissance spécifique employant une topologie originale appelée « machine à modulation de flux ». Cette structure de machine est étudiée depuis plusieurs années à l'Université de Lorraine au sein du Groupe de Recherche en Énergie Électrique de Nancy (GREEN), laboratoire dans lequel cette thèse s'est déroulée. Les travaux relatés dans ce manuscrit interviennent dans le cadre d'une convention CIFRE avec l'entreprise SAFRAN. Afin de permettre l'étude de cette machine, ce mémoire comporte deux chapitres dédiés à la modélisation électromagnétique semi-analytique d'une machine à modulation de flux axiale. L'objectif de ce modèle est de permettre un calcul rapide et précis du couple et des pertes d'une machine. L'utilisation de ce modèle dans le chapitre suivant permet d'aboutir au dimensionnement électromagnétique d'un démonstrateur de 260 kW. Ce dimensionnement tient en outre compte des différentes contraintes techniques et logistiques rencontrées. Un cinquième chapitre détaille la construction en cours du démonstrateur et sa structure mécanique et cryogénique. Enfin le dernier chapitre de ce manuscrit porte sur l'extrapolation des résultats expérimentaux dans le but d'évaluer les performances potentielles des machines à modulation de flux à plus forte puissance
As part of the fight against climate change, the aeronautics industry has set itself the goal of becoming totally carbon neutral by 2050. To achieve this, the use of disruptive technologies is necessary to reduce the emissions of this fast-growing sector. Among these technologies, we find electrification, but its deployment requires high specific power electrical machines. In this context, superconductivity can be a way of improving electrical machines thanks to the high current densities and intense magnetic fields that can be generated with superconducting materials. The main drawback of this technology is the need to operate at cryogenic temperatures. However, the prospect of aircraft using liquid hydrogen as a fuel, transported at -253°C, presents a synergy with superconductivity. It is in this context that the work of this thesis is placed, which aims to study the use of high critical temperature superconducting materials for the development of a high specific power superconducting engine employing an original topology called "flux modulation machine". This machine structure has been studied for several years at the University of Lorraine within the Groupe de Recherche en Énergie Électrique de Nancy (GREEN), the laboratory in which this thesis was carried out. The work reported in this manuscript is part of a CIFRE agreement with the company SAFRAN. In order to allow the study of this machine, this thesis includes two chapters dedicated to the semi-analytical electromagnetic modelling of an axial flux modulation machine. The objective of this model is to allow a fast and accurate calculation of the torque and losses of a machine. The use of this model in the following chapter leads to the electromagnetic dimensioning of a 260 kW demonstrator. This design also takes into account the various technical and logistical constraints encountered. A fifth chapter details the ongoing construction of the demonstrator and its mechanical and cryogenic structure. Finally, the last chapter of this manuscript deals with the extrapolation of the experimental results in order to evaluate the potential performances of flux modulation machines at higher power

43

James, M. P. "Deformation mechanisms for the high temperature Bi-2223 superconductor". Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605023.

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The future application of high temperature superconductors in high field magnets, energy storage, motors and generators, or power transmission depends on the production of long lengths of high quality material. This thesis describes the effect of different deformation mechanisms, during processing, for the high temperature Bi-2223 superconductor produced via the oxide power in tube method. The deformation behaviour of the tape is investigated during both longitudinal and cross rolling, pressing and lubricated pressing, and sequential pressing and lubricated sequential pressing. The emphasis of the study is the effect of deformation on the microstructure and critical current of the conductor. A critical thickness is found to exist during longitudinal rolling, at which point transverse cracks form in the ceramic powder core. Development of these cracks during further rolling is investigated. Cross rolling changes the orientation of the microcracks which inhibit the longitudinal J_c of the conductor. A similar result is found for pressing. Pressing beyond an optimum pressure causes silver penetration into the core. Sintering a tape prior to pressing is found to increase the resistance of silver penetration during deformation. When an industrial lubricant is applied to a tape the deformation path dramatically changes: the silver to superconductor interface area increases, thus increasing the J_c of the tape. A new pressing technique designated "sequential pressing" is developed. This is an efficient process that offers a valuable technique for producing long lengths of high quality Bi-2223 tape with the beneficial characteristics of pressed rather than rolled tape. Hot and cold pressing of Bi-2223 is modelled through the construction of densification mechanism maps. Data from two types of powder shows good correlation to the theoretical time contours on the maps. A temperature-density deformation map was also created for a Bi-2223 tape.

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Zentile, Catherine Lucy. "Transport studies of two classes of high temperature superconductor". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609066.

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Styles, Iain Bruce. "One hole in a high temperature superconductor : Fermi liquid?" Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275708.

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We present a microscopic model of the high temperature superconductors which provides evidence for non-Fermi liquid behaviour. Starting from the Anderson Lattice model, we derive a three-band model of a CU02 plane. We show that the popular t-J model is a subset of our model under certain assumptions which we show to be unphysical. We study the three-band model on the CuO chain. Using two exact solutions of the model to provide trial variational states, and comparing these with an exact finite system numerical calculation, we demonstrate that the spin degeneracy is lifted by the hole motion alone. This provides Heisenberg spin correlations for a physical choice of parameters, and the system is found to be a Luttinger liquid. In two dimensions we numerically solve a series of systems which limit to the CU02 plane. We predict that the CU02 planes will exhibit a highly quantum ground state dominated by short-range dimer correlations, reminiscent of a resonating valence bond state. These predictions are contrary to those of the t-J model, where the hole motion alone predicts huge spin degeneracy for the linear chain, and Nagaoka ferromagnetism for the planar system.

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Perconte, David. "Proximity effect between a high temperature superconductor and graphene". Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS119.pdf.

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Nous avons fabriqué des jonctions YBCO graphène, nous avons étudié dans un premier temps le transport électronique à l'interface entre ces deux matériaux ainsi que le mécanisme - la réflexion d'Andreev - par lequel un courant porté par des électrons est transformé en courant par des paires de Cooper. Nous avons observé des interférences électroniques en fonction du niveau de dopage du graphène. Ces interférences correspondent au tunneling de Klein d'électrons normaux quand l'énergie de ces électrons dépassent le gap supraconducteur. A plus basse énergie, ce sont les paires de Cooper qui passent la barrière par effet tunnel de Klein. Dans un deuxième temps, nous avons fabriqué des jonctions YBCO graphène dont la taille est comparable à la longueur de cohérence du graphène. Nous avons observé d'une part un comportement tunnel de la conductance dans le cas où l'interface graphène YBCO est sale. Dans le cas où l'interface YBCO graphène est propre, nous avons observé des oscillations de la conductance de la jonction en fonction de la tension de biais ainsi que de la tension de grille. Ces oscillations semblent provenir d'interférences électroniques dans le canal de graphène entre les électrodes supraconductrices. Enfin, nous présentons une nouvelle méthode de fabrication de jonction phi à base de BSCCO
We have fabricated YBCO graphene junction. We studied the electronical transport at the interface between these two materials as well as the mechanism - the Andreev reflexion- by which a current carried by electrons is transformed into a current carried by Cooper pairs. We observed electronic interferences as a function of graphene doping. This modulation comes from the presence of a potential barrier at the interface between YBCO and graphene in which the particles are circulating before being transmitted or reflected. These interferences correspond to Klein tunneling of normal electrons when their energy is higher than the superconducting gap. At lower energy, Cooper pairs can traverse the barrier by Klein tunneling. We later fabricated YBCO graphene junctions which size is comparable to the graphene coherence length. We observed tunnel conductance when the interface between graphene and YBCO is opaque. In the case when the interface is transparent, we observed oscillations of the junction conductance as a function of the bias voltage and of the gate voltage. These oscillations seem to originate from electronic interferences inside the graphene channel between the superconducting electrodes. We also propose an experimental method to fabricate phi junction based on BSCCO

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Freitas, Rafael Cassiolato de. "Limitador de corrente eletrica monofasico resistivo supercondutor de alta temperatura critica". [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259009.

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Orientadores: Ernesto Ruppert Filho, Carlos Alberto Baldan
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
Made available in DSpace on 2018-08-13T08:37:22Z (GMT). No. of bitstreams: 1 Freitas_RafaelCassiolatode_M.pdf: 4732668 bytes, checksum: 0819e8d6aca546a3c44b407acd86b0a9 (MD5) Previous issue date: 2008
Resumo: O crescimento da demanda de energia elétrica nos centros urbanos e industriais tem levado à necessidade de expansão dos sistemas de energia elétrica o que tem causado aumento nos níveis de curto-circuito, atingindo o limite da capacidade dos sistemas de proteção existentes exigindo sua substituição por outros de maior capacidade. Nessa situação nem sempre a recapacitação dos sistemas de proteção resolve o problema sendo necessário duplicar circuitos. Para postergar investimentos ou para funcionar na rede juntamente com o disjuntor ou ainda, para proteger os circuitos existentes quando conectados a geradores distribuídos, os limitadores de corrente instalados em série com os disjuntores atuais permitem limitar a corrente de falta, principalmente nos primeiros 100ms até a atuação do sistema de proteção. Dentre os diversos tipos de dispositivos limitadores de corrente elétrica existentes no mercado e também ainda em pesquisa atualmente, os construídos a partir de materiais supercondutores possuem a vantagem de proporcionar limitação de corrente elétrica praticamente instantânea causando mínima interferência no funcionamento normal dos sistemas de energia elétrica. Neste trabalho foram estudadas diversas configurações de limitadores de corrente elétrica utilizando fitas de materiais cerâmicos supercondutores de alta temperatura crítica (HTS), de modo especial os limitadores resistivos em forma de bobinas helicoidais enroladas com fita supercondutora BSCCO. Foi desenvolvida metodologia para o cálculo eletromagnético, projeto, construção e ensaio das bobinas supercondutoras do limitador de corrente, bem como se procurou caracterizar eletricamente a fita HTS sob influência de campo magnético externo com o objetivo de determinar as condições de corrente elétrica e de campo magnético sobre ela aplicado para a transição do estado supercondutor para o estado condutor normal do material ("quench"). Ao final do trabalho foram construídos e ensaiados dois protótipos limitadores de corrente elétrica supercondutores mostrando que, apesar da fita HTS de BSCCO ainda não possuir características adequadas para aplicação em limitadores de corrente, com a esperada evolução destes materiais já existe disponível a técnica para projetá-los e construí-los.
Abstract: The growth in demand of electric energy in urban and industrial centers has lead to the need of expansion of the electrical systems which has caused increase in short circuit levels, reaching the limit capacity of the existing protection systems requiring its replacement by others of greater capacity. In these situations the upgrade of protection systems does not always solve the problem being necessary the circuit's duplication. To postpone investments, to operate together in the electrical system with the circuit breakers or even to protect the existing circuits when connected to distributed generators, fault current limiters should be installed in series with the circuit breakers allowing to limit fault currents, specially in the first 100m until the protection system is triggered. Among the many different types of fault current limiter devices existing in the market and which are under development, the ones made of superconducting materials have the advantage of providing practically instantaneous fault current limitation causing minimum interference in the normal operation of the electrical systems. In this work many configurations of electric fault current limiters were studied using superconducting ceramic materials of high transition temperature (HTS), specially the resistive superconducting fault current limiters in form of helical coils with BSCCO superconducting tapes. The methodology for the electromagnetic calculation, project, construction and tests of the superconducting coils of the fault current limiter was carried out along with the HTS tape characterization under external magnetic field influence in order to determine the conditions of electric current and magnetic field for the transition from superconducting state to normal conducting state (quench). At the end of this work two fault current limiters were built and tested showing that, although BSCCO HTS tapes yet do not have good characteristics for fault current limiters application, when these materials which tend to be developed reach applicability level, the technique to design and built them is already available.
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica

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Connors, Sean Mark. "Effects of high energy electron irradiation on a YBa_x001B_b2_x001B_sCu_x001B_b3_x001B_s0_x001B_b7_x001B_s- high temperature superconductor". Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28145.

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Rayner, Simon. "Positron annihilation studies of high temperature superconductors and related compounds". Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291668.

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Shunmugavel, Karthikeyan. "Rapid single flux quantum logic in high temperature superconductor technology". Enschede : University of Twente [Host], 2006. http://doc.utwente.nl/57620.

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Tesi sul tema "High critical temperature superconductor"

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