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High-temperature superconductivity (HTS) was supposed to change the world. And it did, albeit less dramatically than previously predicted over 40 years ago. Thin films of HTS materials have been applied in qubits for quantum computing, analog-to-digital converters, and neuromorphic circuits; and are necessary for the most sensitive magnetometers used in geological surveys and medical technology. This technological revolution hinges on Yttrium Barium Copper Oxide, or YBa2Cu3Ox+6 (YBCO). This ceramic oxide from the cuprate family has been the benchmark for “high temperature” superconductors, in which the superconducting state is reached above the boiling temperature of nitrogen. However, its processing and technical implementation in thin films come with challenges. It is a non-stoichiometric crystal, and its superconducting properties are highly dependent on its concentration of oxygen (and therefore the variable oxidation state of copper). Most importantly – and the focus of this dissertation – is its stability as a thin film under 40 nanometers thick: YBCO expands differently from its substrates under thermal cycling, loses oxygen at high temperatures, and in air, reacts to form non-superconducting (and oxygen-depleted) products. The work presented here explores how YBCO thin films fail, and how to protect their surface and preserve thin-film superconductivity. The focus lies on the use of bromine – a halogen that tightly binds to the YBCO surface – as a means of chemical passivation, protecting YBCO from being reduced in the atmosphere without harming the desirable superconducting properties, and also without harming the performance of superconducting devices such as YBCO-based nanoelectronics. We found that thermal stress is not the root cause of failure in superconducting thin films, which led the study into further chemistry. Remarkably, treatment with dilute bromine in ethanol solutions was found to have little effect on the material’s performance and does not destroy the electronic properties of Josephson Junctions. The reaction, while an etching process, only attacks the surface, leaving the underlying material (and written junctions) intact. Through this work, we aim to increase the longevity of HTS nanoelectronics. This dissertation uses the toolkits of chemistry to solve problems in electrical engineering – ultimately inching closer to less expensive, more robust HTS devices.

Subject and Purpose. The mechanism of destruction of the S-state of a nonlinear high-temperature superconductor as part of a coplanar waveguide has not been properly elucidated as the effect of avalanche-type transition to a highly dissipative state, which was experimentally detected by the authors, takes place. The present work is concerned with the development of an appropriate approach describing kinetics of destruction of the S-state of a nonlinear high-temperature superconductor in a coplanar waveguide with allowances made for an inhomogeneous distribution of the microwave current in the superconducting film strip. Methods and Methodology. Use of I.B. and O.G. Vendiks’ reasoning [2] is made on kinetics of the destruction of the superconducting state of a wide film when a direct current governed by the time-dependent Ginzburg-Landau equation is applied. Keeping unchanged their idea as to the S–N boundary forming in the film strip with the boundary movement to the middle of the strip, the S–N boundary motion equation is obtained for a coplanar waveguide, proceeding in doing this from the motion equation of magnetic flux vortices under certain restrictions specified. Results. The time of S-state destruction has been numerically estimated: 1) for a wide superconducting film of YBa2Cu3O7–d composition, the destruction is by the direct current and 2) for a coplanar waveguide based on the same film, the destruction is by the microwave current. When the superconductivity is small (I / I c ³ 1), the destruction time values in both cases are close to each other within the order of magnitude. Conclusion. It is for the first time that the S-state destruction time in a coplanar waveguide has been expressed in terms of the microwave current distribution in the waveguide. It has been shown that this characteristic linearly depends on the ratio between the critical current and the microwave current amplitude in contrast to a quadratic dependence obtained for a superconducting strip with a direct current.

This document presents a study on the optimization of the 3D geometry of a horizontal axis radial levitation bearing with zero-field cooled (ZFC) high-temperature superconductor (HTS) bulks in the stator, and radially magnetized permanent magnet (PM) rings in the rotor. The optimization of component dimensions and spacing to minimize the volume or cost concerning only the maximization of the levitation force was previously studied. The guidance force and guiding stability depend on the spacing between PM rings in the rotor and between the rings of HTS bulks in the stator. This new optimization study aims to find the optimum spacing that maximize the guidance force with given HTS bulk and PM ring dimensions while maintaining the minimum required levitation force. Decisions are taken using the non-dominated sorting genetic algorithm (NSGA-II) over 3D finite element analysis (FEA). A simplified electromagnetic model of equivalent relative permeability is used on 3D FEA to reduce numerical processing and optimization time. Experimental prototypes were built to measure magnetic forces and validate appropriate values of equivalent magnetic permeability. An analysis of stable and unstable geometry domains depending on the spacing between rings of HTS bulks and PM rings is also done for two HTS bulk sizes.

This paper deals with a homopolar synchronous machine (HSM) applying high-temperature superconducting (HTS) field coils. Superconductors, especially high-temperature superconductors, have high potential as advanced materials for next-generation electrical machines due to their high critical current density and excellent mechanical strength. However, coils made with high-temperature superconductors have a high risk of being damaged in the event of a quench due to the intrinsic low normal zone propagation velocity (NZPV). Therefore, the coil protection issue has been regarded as one of the most important research fields in HTS coil applications. Currently, the most actively studied method for quench protection of the HTS coils is the no-insulation (NI) winding technique. The NI winding technique is a method of winding an HTS coil without inserting an insulating material between turns. This method can automatically bypass the current to the adjacent turn when a local quench occurs inside the HTS coil, greatly improving the operating stability of the HTS coils. Accordingly, many institutions are conducting research to develop advanced electrical machines using NI HTS coils. However, the NI HTS coil has its intrinsic charge/discharge delay problem, which makes it difficult to successfully develop electrical machines using the NI HTS coil. In this study, we investigated how this charging/discharging problem appeared when the NI HTS coil was used in an HTS homopolar synchronous machine (HSM) which is one of the electrical machines with a high possibility of applying the HTS coil in the future because it has a stationary field coil structure. For this, the characteristic resistances of HTS coils were experimentally obtained and applied to the simulation model.

Plasmonics, as a rapidly growing research field, provides new pathways to guide and modulate highly confined light in the microwave-to-optical range of frequencies. We demonstrated a plasmonic slot waveguide, at the nanometer scale, based on the high-transition-temperature (Tc) superconductor Bi2Sr2CaCu2O8+δ (BSCCO), to facilitate the manifestation of chip-scale millimeter wave (mm-wave)-to-terahertz (THz) integrated circuitry operating at cryogenic temperatures. We investigated the effect of geometrical parameters on the modal characteristics of the BSCCO plasmonic slot waveguide between 100 and 800 GHz. In addition, we investigated the thermal sensing of the modal characteristics of the nanoscale superconducting slot waveguide and showed that, at a lower frequency, the fundamental mode of the waveguide had a larger propagation length, a lower effective refractive index, and a strongly localized modal energy. Moreover, we found that our device offered a larger SPP propagation length and higher field confinement than the gold plasmonic waveguides at broad temperature ranges below BSCCO’s Tc. The proposed device can provide a new route toward realizing cryogenic low-loss photonic integrated circuitry at the nanoscale.

We prepared overlap soldered joints of high-temperature superconducting tapes, using various materials and preparation conditions. In order to select the joints with optimal performance, we correlated their electrical properties (derived from current–voltage curves) with the microstructure of the respective joint cross-section by scanning electron microscopy. With the first group of joints, we focused on the effect of used materials on joint resistivity and critical current, and we found that the dominant role was played by the quality of the internal interfaces of the superconducting tape. Initial joint resistivities ranged in the first group from 41 to 341 nΩ·cm2. The second group of joints underwent a series of thermal cyclings, upon which the initial resistivity range of 35‒49 nΩ·cm2 broadened to 25‒128 nΩ·cm2. After the total of 135 thermal cycles, three out of four joints showed no signs of significant degradation. Within the limit of 100 thermal cycles, reliable soldered joints can be thus prepared, with normalized resistivity not exceeding 1.4 and with normalized critical current above the value of 0.85.

High-performing superconducting YBa2Cu3O7–x (YBCO) films are fabricated by a chemical solution deposition methodology through novel barium-deficient low-fluorine solutions. The precursor solutions, distinguished for being straightforward, inexpensive and eco-friendly, allow us to reduce the growing temperature of YBCO down to 750 °C. We investigated the influence of the growing temperatures on both the microstructure and superconducting properties of YBCO films by using conventional thermal annealing and flash-heating approaches. A clear correlation between the growing temperature (Tg) and the superconducting performance of the films was obtained with improved performances observed at low Tg., This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom Research and Training Programme 2014–2018 and 2019–2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. We acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496, FUNFUTURE CEX2019-000917-S), SUMATE project RTI2018-095853-B-C21, cofinanced by the European Regional Development Fund, COST-Nanocohybri CA16218 and Catalan Government with 2017-SGR-1519 and XRE4S.

We enhanced the performance of superconducting tapes during quenching by coating the tapes with various composites, with regards to the application of such coated systems in superconducting fault current limiters. In composition of the coating, we varied the type of epoxy matrix, the content of ceramic filler particles and the use of reinforcement in order to optimize the thermal and the mechanical stability of the coated tapes. By this way modified superconducting tapes were able to reduce the maximum temperature 170 &deg, C of not modified superconducting tape to 55 &deg, C during the quench with electric field up to 130 V m&minus, 1.

Air-core high-temperature superconducting quadrupole magnets (AHQMs) differ from conventional iron-core quadrupole magnets, in that their iron cores are removed, and instead high-temperature superconductors (HTSs) are applied. The high operating temperature and high thermal stability of HTS magnets can improve their thermodynamic cooling efficiency. Thus, HTS magnets are more suitable than low temperature superconducting magnets for withstanding radiation and high heat loads in the hot cells of accelerators. AHQMs are advantageous because they are compact, light, and free from the hysteresis of ferromagnetic materials, due to the removal of the iron-core. To verify the feasibility of the use of AHQMs, we designed and fabricated a 3.0 T/m AHQM. The magnetic field properties of the fabricated AHQM were evaluated. Additionally, the characteristics of the air-core model and iron-core model of 9.0 T/m were compared in the scale for practical operation. In comparison with the iron-core model, AHQM significantly reduces the critical current (IC) due to the strong magnetic field inside the coil. In this study, a method for the accurate calculation of IC is introduced, and the calculated results are compared with measured results. Furthermore, the optimal shape design of the AHQM to increase the critical current is introduced.

The LHD-type helical fusion reactor FFHR has been studied to realize steady-state fusion power generation without a need for current drive and free from disruption. The conceptual design studies of FFHR are steadfastly progressing based on the presently ongoing experiments in the Large Helical Device (LHD). In order to enhance the attractive features of the base option of FFHR-d1A, which is similar to LHD, configuration optimization is being considered for FFHR-d1C. Slight modification of the helical coil trajectory gives an improved condition both for the plasma confinement and the MHD stability. In order to overcome the difficulty for construction and maintenance associated with the three-dimensional structure, innovative ideas are being explored for the superconducting magnet, divertor, and blanket. For the superconducting helical coils, the joint-winding method confirms a fast manufacturing process. The helical divertor is reexamined and practical feasibility is discussed. The maintenance method of the helical divertor and the helically-segmented breeder blanket is a serious issue and a plausible solution is proposed.

Non-insulation high-temperature superconducting coils provide a much lower risk of burnout in fault/abnormal conditions, such as hot-spot quench and overcurrent. This study employs an equivalent circuit grid model, coupled with magnetic field calculation and the E–J power law of superconductors, to deeply and systematically investigate the overcurrent charging process in a double-pancake non-insulation coil. An evident saturation of the magnetic field in the axial direction of the coil was observed and verified by experiments. Experimentally, the entire process, including the behavior of the magnetic field, was consistent with the numerical results. Based on the verified model, two main points were addressed: (1) Transient current distribution inside the coil during overcurrent charging was studied. Potential quenching risks were found to be at the innermost and outermost turn near the electrodes, as well as the pancake-to-pancake connection part. (2) Magnetic field saturation, which is a unique phenomenon in non-insulation superconducting coils during overcurrent charging, was studied in detail and first quantitatively defined by a new concept “converged load factor”. Its relationship with turn-to-turn resistivity was revealed.

In this paper, a new method is presented for sensitive quench detection in high-temperature superconductor (HTS) rotating machinery. The normal zone propagation velocity of an HTS is about 1000 times slower than that of a low-temperature superconductor. Therefore, the propagation of normal zone resistance, which occurs when the HTS transits from the superconducting state to the normal state, is also slower. Thus, it is difficult to detect the abnormal signals by voltage measurement using voltage taps. Moreover, the monitoring signal includes noise generated by interaction between the HTS rotating machinery and the industrial environment. Therefore, when quenching occurs in the HTS rotating machinery, a thermal runaway occurs in the hot spot. Furthermore, the magnetic energy stored in the HTS coil can damage the machinery. For these reasons, a new method is proposed for sensitive quench detection that reduces the noise generated from the power supply and from the HTS rotating machinery, using both an RLC resonance circuit and fast Fourier transform analysis.

Superconductors are essential in many present and future technologies, from large-scale devices for medical imaging, accelerators, or fusion experiments to ultra-low-power superconducting electronics. However, their potential applicability, and particularly that of high-temperature superconductors (HTS), is severely affected by limited performances at large magnetic fields and high temperatures, where their use is most needed. One of the main reasons for these limitations is the presence of quantized vortices, whose movements result in losses, internal noise, and reduced performances. The conventional strategy to overcome the flow of vortices is to pin them along artificial defects. Here, we theoretically and experimentally demonstrate that critical-current density in high-temperature superconductors can reach unprecedented high values at high fields and temperatures by preventing vortex entry. By tailoring the geometry, that is, reducing the width, W, of nanowire-patterned HTS films, the range of the Meissner state, for which no vortices are present, is extended up to very large applied field values, on the order of ∼1 T. Current densities on the order of the depairing current can be sustained under high fields for a wide range of temperatures. Results may be relevant both for devising new conductors carrying depairing-current values at high temperatures and large magnetic fields and for reducing flux noise in sensors and quantum systems., We acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa” Programme for Centres of Excellence (SEV-2015-0496), COACHSUPENERGY project (MAT2014-51778-C2-1-R), and SuMaTe (RTI2018-095853-B-C21) cofinanced by the European Regional Development Fund, and project MAT2016-79426-P (Agencia Estatal de Investigacion/Fondo ́ Europeo de Desarrollo Regional). We also thank support from the European Union for NANOCOHYBRI project (Cost Action CA 16218) and from the Catalan Government projects SGR-2017-1519 and 2017-SGR-105. A.S. acknowledges a grant from ICREA Academia, funded by the Generalitat de Catalunya. V.R. Acknowledges EU H2020 research and innovation programme (Marie Sklodowska-Curie IF grant agreement OXWALD 838693). We acknowledge the use of ICTS-CNM facilities and ICMAB scientific and technical services. We thank Alexey V. Pan for fruitful discussions.

Background Dielectric properties and ac conductivity were studied and correlated with the structure of a series of YBCO ceramic, doped with different doping levels ranging from 0.1 to 0.5 wt.% of magnetic nano-metal oxides, namely Mn3O4, Co3O4, and Cr2O3. The most important feature of this study was the ultrahigh values of dielectric constants at a low frequency, exactly 50 Hz. We found that the undoped YBCO has a value of ε′ equal to 6.99 × 106 at 50 Hz at room temperature which was increased to 1.09 × 108 at 120 °C, higher than any other ferroelectric material. Moreover, the value of ε′ depends on the nature and the value of the magnetic moment of the doped metal oxides. The value of ε′ is at least three orders of magnitude greater than any previously studied composites which suggest that this perovskite ceramic material can be used to create electrostatic capacitors with energy far better than the best electrode double-layer capacitors (EDLC). Additionally, ac electrical conductivity has two frequency-dependent regions, the low frequency, where σ ac is independent of frequency, and the high-frequency region where dispersion occurs. The ac conductivity measurement with frequency leads us to conclude that the conduction mechanism in the studied samples can be correlated barrier hopping (CBH) model. Results The dielectric properties of undoped YBCO ceramics at 50 Hz in temperature ranging from room temperature to 120°C were studied. It is obvious that the dielectric constant and dielectric loss of YBCO decrease with increase in frequency and temperature. It can be noticed that dielectric constant of YBCO increases at 50 Hz from 6.99 × 106 at room temperature to 1.09 × 108 at 120°C. The high values of ε′ recorded for YBCO doped with Mn3O4 varied from 9.45 × 105 to 15.5 at room temperature and 1.34 × 105 to 9.242 at 1 MHz at 120°C. For doped YBCO with Co3O4, the values of ε\ varied from 9.5 × 105 at 50 Hz to 13.24 at 1 MHz at room temperature, with changes from7.8 × 104 at 50 Hz to 53.42 at 1 MHz. For YBCO ceramic samples doped with Cr2O3, ε′ varied from 1.138 × 106 at 50 Hz to 8.38 × 103 at 1 MHz at room temperature and from 5.935 × 105 at 50 Hz to 3.53 × 103 at 1 MHz at 120°C. The ac conductivity was further studied for undoped YBCO and doped YBCO with 0.1 wt.% of nano-metal oxide of Cr2O3, Co3O4, and Mn3O4 samples. For all the studied samples, we found σ ac is typically specified to the hopping conduction and ac conductivity has a power law behavior in terms of frequency (ω). In general, there are two frequency-dependent regions for all the studied ceramic samples; in the low-frequency region, σ ac is independent of frequency whereas in the high-frequency region, dispersion occurs. The change in microwave conductivity of the studied samples with frequency (1–5 MHz) is shown in Fig. 5. It is observed that for all samples, the conductivity increases with temperatures and depends on the doped metal oxide. The values of σ ac at 5 MHz varied from − 0.4 to 1.2 for undoped YBCO, from − 0.98 to − 0.75 for 0.1 wt.%Mn3O4-YBCO sample, from − 0.25 to 0.2 for 0.1 wt.% Co2O3-YBCO sample, and from − 0.4 to 0.6 for 0.1 Wt.% Cr3O4-YBCO sample. Conclusion The primary finding in this paper is of empirical investigation. YBCO, which is a high-temperature superconductor, has a high dielectric constant ε′ ranging from 6.99 × 106 at room temperature to 1.09 × 108 at 120°C. This value is at least three orders of magnitude greater than any previously studied composites which suggest that this perovskite ceramic material can be used to create electrostatic capacitors with energy far more efficient than the best electrode double layer capacitors (EDLC).

We have been developing an AC power source with a high-temperature superconducting (HTS) transformer that is small and can supply a large AC current. The HTS transformer needs a detection system of normal transition for high reliability. We have proposed the active power method as the detection system. The system enabled early detection of the normal transition in a secondary coil of the transformer, which was wound with a bundle of some HTS tapes. However, we could not identify the normally transited HTS tape in bundle conductors using the conventional method. Therefore, in this paper, we propose a method to identify the normally transited HTS tape in the bundle conductor by improving the active power method. The improved method is based on measuring the active power in each HTS tape in the bundle conductor. Experiment results show that the proposed method works successfully for early and accurate identification under outputting a secondary maximum current of 1 kApeak at 1 kHz.

International audience; We developed a simple and stable precursor solution containing low fluorine content to fabricate YBa2Cu3Oy (YBCO) films on CeO2/YSZ/CeO2 buffered NiW substrates. The fluorine content in the precursor solution could be controlled at 23.1% by tuning the ratio of barium trifluoroacetate to barium acetate. Fast pyrolysis process and smooth surface of YBCO precursor films could be acquired by using the low-fluorine solution. The phase, texture,microstructure, and superconducting properties of YBCO film were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, and four-probe method, respectively. The crystallized YBCO film showed good out-of-plane and in-plane textures. A high critical current density Jc of ∼3 MA/cm2 (77 K, 0 T) could be obtained in the YBCO/CeO2/YSZ/CeO2/NiW sample derived from the low-fluorine solution. The results indicate that the controllable fluorine content solution could be useful for epitaxial growth of YBCO films on buffered NiW substrates.

Stacks of high-temperature superconducting tape have proved to trap in laboratory conditions levels of magnetic flux density one order of magnitude above actual state-of-the-art permanent magnets. Their simple manufacturing, high mechanical properties and intrinsic resistance to sudden quench greatly facilitate their utilization in industrial applications, amongst them, as a source of magnetic flux density in the rotor of electrical machines. For this to happen, the currents induced in the superconducting layers of the stack must not be disturbed during operation. This work studies in experimental conditions the demagnetization of a stack rotating in the airgap of an electrical motor under slot and winding-induced cross-field components, whose values are estimated via conventional 2D finite element analysis. The results are congruent with previous laboratory studies and show small long-term demagnetization rates that may allow operation for time spans longer than initially established.

WOS: 000362585600005 The influence of a ferromagnetic substrate on microwave surface resistance of high-temperature superconductors is numerically studied through finite element method computations. For a superconductor with a ferromagnetic substrate underneath, it is observed that an increase in ferromagnet susceptibility results in more shielding of the superconductor from the influence of external magnetic field and, in turn, a fall in microwave surface resistance. The effect saturates with higher susceptibilities where a plateau is reached in the surface resistance curve. As a comparison, coating superconductor with U-shaped ferromagnets on two sides is also considered where an ordinary hysteresis curve in terms of microwave surface resistance is observed for a non-magnetic coating. In contrast, a highly ferromagnetic coating with a relative permeability of 1000 gives rise to an unusual hysteresis behavior. Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [111T715] This study is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under the grant number 111T715.

Sumitomo Heavy Industries, Ltd. (SHI) developed a high-power Stirling-type pulse tube cryocooler for cooling high-temperature superconductor (HTS) devices, such as superconductor motors, superconducting magnetic energy storage (SMES), and fault current limiters. The experimental results of a prototype pulse tube cryocooler were reported in September 2013. For a U-type expander, the cooling capacity was 151 W at 70 K with a compressor input power of 4 kW. Correspondingly, the coefficient of performance (COP) was about 0.038. However, the efficiency of the cryocooler is required to be COP > 0.1 and it was found that, theoretically, it is difficult to further improve the efficiency of a pulse tube cryocooler because the workflow generated at the hot end of the pulse tube cannot be recovered. Therefore, it was decided to change the expander to a free-piston type from a pulse tube type. A prototype was developed and preliminary experiments were conducted. A cooling capacity of 120 W at 70 K with a compressor input power of 2.15 kW with corresponding COP of 0.056, was obtained. The detailed results are reported in this paper.

The power handling capability of a high temperature superconducting transmit filter with a double-strip resonator (DSR) was investigated by comparing the performances of such a filter with conventional microstrip-line (MSL) filter. The DSR structure consists of two coupled strips and the center pin of the SMA connector as feed line. The idea is to increase the effective film thickness to reduce the current concentration at the edges of the resonator compared with that of an MSL resonator. The two three-pole filters were designed using electromagnetic simulator. The center frequency and 3dB-bandwidth are a 5.0-GHz and a 100-MHz. The two filters were fabricated using YBa 2 Cu 3 O y thin films on a CeO 2 -buffered r-Al 2 O 3 substrate. The measured frequency responses of the filters were in reasonable agreement with the simulated ones. The measured power handling capability of the DSR filter was 3.5 dBm larger than that of the MSL filter.

The superconducting properties of YBa2Cu3O7-δ (YBCO) film can be significantly improved through the introduction of nanosized defects. In this work, the Chemical Solution Deposition (CSD) of YBCO film doped with Nanodiamond (ND) is proposed. ND introduction in YBCO (YBCO-ND) has never been reported until our recent preliminary study [1] that showed ND potential for the improvement of YBCO transport properties. Further optimizations of the YBCO-ND CSD process have been accomplished and results are illustrated in the present paper. Good epitaxial films have been obtained and a significant improvement of film morphology and superconducting properties has been observed with respect to pure YBCO. Dopant seems to have a beneficial effect on YBCO morphology. In fact, YBCO-ND films generally show denser, smoother and more connected surfaces. The good morphology corresponds to increased superconducting properties. Higher zero-field critical current densities have been measured in the temperature range from 10 K to 77 K (i.e. 18 and 13 ± 1.2 MA•cm−2 respectively for YBCO-ND and pure YBCO at 10 K). These results could be mainly ascribed to an improvement of the percolation path due to the increase of film density and grain coalescence. It might be supposed that ND influences the nucleation mechanisms of YBCO films facilitating c-axis orientation, but the actual role sill needs to be clarified.

A phenomenological model has been proposed to describe the avalanche-like transition of a microwave nonlinear HTSC-based transmission line into a dissipative state. This effect was observed by the authors in a dc-biased transmission line. The proposed model generalizes the well-known phenomenological model for the nonlinear HTSC-based transmission line under the action of a direct current. The character of the dependences obtained for microwave losses allows the jump-like changes in the properties of the nonlinear HTSC-based transmission line to be regarded as a fold-type catastrophe and the methodological and mathematical apparatus of the theory of catastrophes to be used in order to explain the results obtained and predict new ones., У данiй роботi пропонується феноменологiчна теоретична модель лавиноподiбного переходу мiкрохвильової нелiнiйної ВТНП лiнiї передачi в дисипативний стан. Цей ефект спостерiгався авторами в лiнiї передачi з постiйним струмом. Запропонована модель узагальнює вiдому феноменологiчну модель нелiнiйної ВТНП лiнiї передачi при впливi на неї постiйного струму. Характер поведiнки залежностей мiкрохвильових втрат, що дослiджуються, дозволяє розглядати стрибкоподiбнi змiни властивостей нелiнiйної ВТНП лiнiї передачi, як “катастрофу” типу “складки” i використовувати методологiчний i математичний апарат теорiї “катастроф” для пояснення отриманих i передбачення нових результатiв.

Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212) superconducting whiskers, owing to their microscopic size, are good candidates for the fabrication of miniaturized devices for production/sensing of THz-radiation based on their Intrinsic Josephson Junctions (IJJ) properties. With this respect, several studies demonstrated the possibility of controlling whisker IJJ parameters by modifying the oxygen content. In this paper we show that both thermal annealing and hard X-ray irradiation are effective ways to tune the oxygen doping. In particular, we monitored the effect of an annealing process at 363 K and of irradiation by 17 keV micro- and nano-beams on the structural and superconducting properties of selected Bi-2212 whiskers. Moreover we modeled by a finite element simulation the temperature field induced by the X-ray beam to try to clarify the origin of the measured changes.

Single filament Ag sheathed Bi2.1Sr1.96Ca x Cu2O8+δ (Bi-2212) tapes with different Ca content of x =0.90, 0.95, 1.00, and 1.05, were prepared by powder in tube (PIT) process. The critical current density and flux pinning properties have been systematically studied with the variation of Ca content. X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been performed for the characterization of the tapes. Although the maximum critical current density, J c, was obtained from the stoichiometric sample under zero field, the nonstoichiometric Ca content are beneficial for the improvement of J c under magnetic field, due to the enhancement of flux pinning. The J c value of 950 A/cm2 has been obtained at 0.15 T, which is over 30% higher than that from x =1.00 tape.

Theoretical methods of calculating of two-dimensional magnetic fields, inductive parameters and output characteristics of the new type of high-temperature superconducting (HTS) synchronous motors with a composite rotor are presented. The composite rotor has the structure containing HTS flat elements, permanent magnets and ferromagnetic materials. The developed calculation model takes into account the concentrations and physical properties of these rotor elements. The simulation results of experimental HTS motor with a composite rotor are presented. The application of new type of HTS motor in different constructions of industrial high dynamic drivers is discussed.

The proposed study investigates the aging of two precursor solutions used for the chemical solution deposition of YBa2Cu3O7-x (YBCO) and composite YBCO films with nanostructured inclusions of BaZrO3 (YBCO-BZO). The stability of precursor solutions plays a crucial role in determining the crystalline quality and the superconducting properties of YBCO films. Although low- or free-fluorine solutions are promising in order to improve the synthesis route and to reduce the environmental impact, the poor stability of the solution is the major drawback of the low-fluorine precursors since they degrade faster (4-6 weeks) than other precursor solutions for superconducting layers (e.g., trifluoroacetates solutions are stable up to 6 months) or buffer layers (stable for several months). Therefore, a deeper comprehension of the degradation mechanisms is fundamental to properly optimize the composition of the precursor solution. The current work studies two precursor solutions (for YBCO and YBCO-BZO) that are complex systems, in which different interactions need to be considered: most of all, the nature of ligands (acetate, propionate, ammonia) that complex each metal and influence not only the solution stability but also the quality of the deposited film. Thus, information obtained from different analyses is correlated with morphological, structural, and superconducting properties of the deposited film in order to understand the underlying chemical mechanisms of aging (salts precipitation, oxidation, polymerization) and its effects. © 2002-2011 IEEE.

The transport properties of nanocomposite YBa 2 Cu 3 O 7-x (YBCO) films grown by metal-organic decomposition (MOD) and prepared with a low-fluorine-coating solution on SrTiO 3 single-crystal substrates were studied with dc and microwave measurement techniques. As demonstrated in previous studies, the combination of these two techniques is a powerful tool for vortex pinning investigation. The BaZrO 3 inclusions (BZO) as artificial pinning centers were introduced into the YBCO matrix by the excess of corresponding Ba and Zr precursor salts to the initial YBCO precursor solution up to 5 mol%. The effect of BZO was clearly observed in magnetic field dependence relations of critical current density (J c ) and the complex surface impedance, i.e., ΔZ, at fixed temperature and magnetic field parallel to the c-axis. The result shows that BZO particles mainly act as isotropic pinning centers. The short-range vortex dynamics was probed by the ~47.7-GHz microwave surface impedance technique. The derived vortex parameters r and k p were sensitive to the presence of nanoparticles, indicating the effect of BZO on pinning. The joint field dependence relations of J c and k p help in elucidating the pinning regime in our nanocomposite MOD YBCO/BZO films.

A small mesa structure (10 /spl mu/m /spl times/ 10 /spl mu/m, 15 nm thick) of intrinsic Josephson junctions in Bi/sub 2/Sr/sub 2/CaCu/sub 2/o/sub 8+/spl delta// is employed to observe the tunneling characteristics and the superconducting gap magnitude by short pulse technique (short pulse interlayer tunneling spectroscopy). In the measurement on 60 ns time scale, the effect of self-heating is almost negligible in the sample, whose resistivity is as small as 10 /spl Omega/cm. In slightly overdoped region, the maximum Josephson current density increases from 0.85 to 2.1 kA/cm/sup 2/ with increasing doping level. The superconducting gap magnitude 2/spl Delta/ decreases from 62 to 37 meV with increasing doping level. The value for 2/spl Delta//k/sub B/T/sub c/ decreases from 8.3 to 5.2 with increasing doping level. These values in slightly overdoped region are smaller than those in optimum and underdoped region.

Nanowires of Y-Ba-Cu-O, with the thickness of 50 nm and the width ranging from 90 nm to 500 nm have been successfully grown on lanthanum aluminate substrates for photon detection experiments. The nanowires were up to 10-mu m long and formed a meander structure, covering the area of up to 30x10 mu m(2) with a fill factor of 50%. The samples were excited using optical laser pulses at a 1550 nm wavelength and resulting photoresponse signals were measured as a function of both temperature and normalized bias current. Presence of two, distinct regimes in the photoresponse temperature dependence has been clearly evidenced, suggesting different physical mechanisms of the signal formation. Presented experimental results shed new light on prospects of implementation of high-temperature superconducting oxides in photon detection and counting.

The superconducting behaviour of the system TlBa 2− x La x CuO 5− y has been investigated. Samples prepared by the procedure described in this paper show a decrease in T c with increasing lanthanum concentration. This is in contrast to the trend reported by other authors [15, 19]. This difference in behaviour was explained in terms of the oxygen deficiency y in the parent compound TlBa 2 CuO 5− y .

A Ge pixel array detector (PAD) with 100 segments was used in fluorescence x‐ray absorption spectroscopy (XAS) study, probing local structure of high temperature superconducting thin film single crystals. Independent monitoring of individual pixel outputs allows real‐time inspection of interference of substrates which has long been a major source of systematic error. By optimizing grazing‐incidence angle and azimuthal orientation, smooth extended x‐ray absorption fine structure (EXAFS) oscillations were obtained, demonstrating that strain effects can be studied using high‐quality data for thin film single crystals grown by molecular beam epitaxy (MBE). The results of (La,Sr)2CuO4 thin film single crystals under strain are related to the strain dependence of the critical temperature of superconductivity.

A fast and stable method is proposed for calculating the time-varying shielding current density in a high-temperature superconducting (HTS) film containing cracks. If an initial-boundary-value problem of the shielding current density is formulated by the T-method, integral forms of Faraday's law on crack surfaces are also imposed as boundary conditions. As a result of the spatial discretization of the initial-boundary-value problem, semi-explicit differential algebraic equations (DAEs) are obtained. Although the DAEs can be solved with standard ordinary-differential-equation (ODE) solvers, much CPU time is required for their numerical solution. In order to shorten the CPU time, the following high-speed algorithm is proposed: the block LU decomposition is incorporated into function evaluations in ODE solvers. A numerical code is developed on the basis of the proposed algorithm and detectability of cracks by the scanning permanent-magnet method is numerically investigated. The results of computations show that, when multiple cracks is contained in an HTS film, resolution of the scanning permanent-magnet method will be degraded remarkably.

Configuration optimization is carried out for the heliotron-type fusion energy reactor FFHR. One of the important issues is to find sufficient clearances between the ergodic region outside the nested magnetic surfaces and blankets at the inboard side of the torus so that direct losses of alpha particles are minimized and the heat flux on the first walls is reduced. The latest design has a fairly large major radius Rc ∼ 17 m of the helical coils in order to satisfy this condition. It has been found, as an alternative design, that equivalent clearances are obtained with Rc = 15 m by employing a lower helical pitch parameter and splitting the helical coils in the poloidal cross-section at the outboard side. Furthermore, splitting the helical coils provides another modified configuration at Rc ∼ 17 m that ensures magnetic well formation in the fairly large nested magnetic surfaces with outward shifted configurations. From the engineering viewpoint, we propose that such helical coils be constructed by prefabricating half-pitch segments using high-temperature superconductors; the segments are then to be assembled on site with joints.

In this contribution, we report on the study of the vortex pinning properties of YBa 2 Cu 3 O 7-δ (YBCO) film grown on decorated substrate to obtain an improvement of magnetic field dependence of the critical current. Surface-decorated SrTiO 3 (STO) substrates have been obtained by polymer assisted deposition (PAD) with BaZrO 3 (BZO) nanoislands uniformly distributed over the substrate surface. Thanks to the high density of the polymer, the viscosity of the solution can be easily adjusted to tune nanoislands' density. Typical values of nanoislands' diameter and height are around 20-50 and 3-5 nm, respectively. YBCO films, derived by metal-organic decomposition (MOD) using low-fluorine precursor solution, were successfully grown on both bare and BZO-decorated STO substrate. Results indicated that surface decoration is effective to enhance pinning at both 77 and 65 K in the whole field range up to 7 T. As a matter of fact, the value of critical current doubled with respect to YBCO film grown on bare STO at 77 K and 1 T. © 2002-2011 IEEE

We propose a novel transmit high-temperature-superconducting (HTS) dual-mode double-strip octagonal patch resonator filter with an additional patch conductor working as a perturbation. The dual-mode double-strip resonator consists of two stacked octagonal patch resonators and an additional patch conductor which is placed between the resonators to provide coupling between the orthogonal resonating modes. This reduces the current concentration at the perturbation compared with that of conventional dual- mode filter with stub perturbation. The bandwidth is adjusted by changing the size of the additional patch conductor. A 2-pole HTS dual-mode double-strip octagonal resonator filter using an additional patch conductor with a 5.0 GHz center frequency and 100 MHz bandwidth was designed using an electromagnetic simulator based on the moment method. The filter was fabricated using YBa2CuO7 thin films on r-Al2O3 substrates. The filter is evaluated by experiment and simulation with good agreement.

A mixed refrigerant cascade presents a potential solution for cooling of high-temperature superconductors between 55 K and 70 K. The envisioned process consists of a pre-cooling and a low-temperature stage, where pre-cooling to 120 K is achieved by a conventional mixed refrigerant cycle. The low-temperature stage operates with a mixture of neon, nitrogen and oxygen at high pressure. Process simulation predicts an overall efficiency of about 8% of Carnot at 55 K. Simulation results for the pre-cooling stage were validated by experiments with an existing test stand.

In this paper, a study of both pure and 5% BaZrO33-doped YBCO low-fluorine coating solutions performed by 1 H-Nuclear Magnetic Resonance (NMR) spectroscopic techniques is presented. This investigation enabled us to unequivocally identify the chemical species involved in the solution aging process. It was found that the presence of traces of methanol, typically used for the preparation of the solutions, promoted methyl propionate formation. Since the methanol concentration reduction in time is not completely balanced by methyl propionate formation, it is supposed that additional esterification reactions involving other acids might occur. The presence of methyl propionate ester was not recognized in solutions obtained through a refining process in which residual methanol traces were fully removed. The modification in time of the solution composition was found to be in strong correlation with the degradation of the film properties for standard solution, whereas no degradation, in the same time frame, was observed for the films prepared with the refined solutions. Indeed, both YBCO and YBCO + 5% BaZrO 3 films, grown with aged refined solutions, exhibit critical temperature values above 91 K and microstructure comparable with the ones recorded in samples obtained with freshly prepared solutions. Even though the exact role of the ester in the YBCO phase formation and film quality could not be identified yet, some possible mechanisms have been proposed and discussed.

We investigated the process for fabricating YBa2Cu3Oy (YBCO) thin film microstrip lines from amorphous thin films. First, we made amorphous YBCO thin films and then post-annealing was carried out. The amorphous 300-nm-thick YBCO thin films were deposited on a CeO2 buffered r-Al2O3 substrate by pulsed laser deposition. The 50-nm-thick CeO2 buffer layer was made by a facing target sputtering system. We examined the optimal conditions of the post-annealing process by using a two-step crystallization process. The heating rate of the first step was set to 360 K/min until 1023 K, and then the heating rate of the second step was set to 20 K/min until 1073 K. The oxygen pressure was kept to 3000 Pa at 1073 K for 210 min. From the XRD measurement, we observed that the YBCO thin films grew c-axis orientation on the CeO2/r-Al2O3 substrate. Both YBCO and CeO2 φ-scan peaks showed four-fold symmetry and rotated 45 degrees between YBCO (102) grain axis and CeO2 (220) grain axis. The surface roughness, Δφ, and Δφ of YBCO thin films were 35.12 nm, 0.89 degree, and 1.51 degree, respectively. We found these to be the optimal post-annealing conditions in which to make a single phase of YBCO films with Tc of 87 K from amorphous YBCO thin films. Therefore, our process is useful to make high-quality YBCO microstrip lines.

The present work is performed within the framework of the EUROfusion DEMO project. Previously, it was demonstrated that for a maintained magnetic flux the use of HTS conductors at highest magnetic field in a layer-wound CS coil would allow the reduction of its outer radius by around 0.5 m as compared to the DEMO reference design using only Nb3Sn conductors. Alternatively, the superior high field performance of HTS conductors can be used to maximize the magnetic flux of a CS coil with a given outer diameter, which could significantly prolong the duration of plasma burn phase and thus the overall power plant efficiency. In the present study, the maximization of the magnetic flux, generated by a layer-wound CS coil of fixed outer radius, is considered. HTS conductors are envisaged to be used at highest field, while Nb3Sn and NbTi are foreseen to be used in intermediate and low field layers, respectively. The inner radius of the CS coil is optimized with respect to the generation of a maximum flux taking into consideration the superconductor properties, the hoop stress and the axial stress. In order to provide reasonable starting values for the finite element analysis, first a simplified model with layer-dependent current densities, however, without stainless steel grading will be considered. In the final outline design of the CS coil a superconductor and stainless steel grading will be implemented.

The traditional all-TFA precursor solution for coated conductors has sensitivity to the heating rate in pyrolysis process. This sensitivity could be weakened by using a modified precursor solution, which was prepared by the mixture of yttrium trifluoroacetate, barium trifluoroacetate, and copper benzoate. The YBCO films were deposited on buffered NiW substrates (NiW/Y2O3/YSZ/CeO2) with the modified precursor solution. The texture, microstructure and superconducting properties of YBCO films were characterized by X-ray diffraction, scanning electron microscopy and four-probe method, respectively. The YBCO films prepared by modified TFA-MOD method demonstrated high performance.

Bi2.1Sr1.96Ca x Cu2.0Ox (Bi-2212) thick films with Ag substrates were prepared through dip coating process. By X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations, the influences of heat treatment parameters on the phase transition process and the aligned growth of Bi-2212 grains have been systematically studied. The maximum heat treatment temperature, T max, and cooling rate, R c has been optimized. Meanwhile, the influences of the coating density on the microstructures and the transport properties have also been discussed by applying an additional cold pressing. The J c value of over 7300 A/cm2 (77 K, self field) has been obtained from the direct powder pressing process, which is over 60% higher than that from the traditional dip coating thick film.

Commercial high-temperature superconducting coated conductors (HTS-CCs) have low thermal diffusivity and nonuniform critical current density. These two factors lead commercial HTS-CCs to a partial quench when they are subjected to a transport current around their average critical current (I-c.av). The consequence is the appearance of localized resistive zones, and a high risk of thermal runaway can arise when HTS-CCs are used for resistive fault current limiter (RFCL) purposes. The enhancement of the normal zone propagation velocity (NZPV) of HTS-CCs is a desirable solution for achieving sufficient thermal stability while keeping the cost of RFCLs under an acceptable threshold. Even though in recent years, several valid methods to increase the NZPV have been proposed, their impact on the design of RFCLs is not clear. For this reason, we developed a one-dimensional numerical model that enables us to simulate HTS-CCs with enhanced NZPV and to study the limitation performance of a HTS-CC-based RFCL in real operating conditions. Our preliminary re sults demonstrate that the NZPV enhancement can effectively limit the needed amount of HTS-CCs with important economic benefits for the design of RFCLs.