YBCO High Temperature Superconductor Research Articles

Understanding ac losses in CORC cables of YBCO superconducting tapes by numerical simulations

Alternating current (ac) losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different ac loss components and provide approaches for reducing ac losses in cables. An FEA model based on the T-A formulation treats the cross section of thin superconducting layers as 1D lines and, therefore, only can predict the ac loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross section HTS tapes to provide the total ac losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. The 1D and 2D simulation models were validated by cross comparing the results from both models and by comparing sub-section and full cross section models. Subsequently, two models relate cable design and operational parameters to the surface and edge losses of a two-layer CORC cable by considering the (1) relative contributions of edge and surface losses to the overall ac losses; (2) effect of the current distribution between inner and outer HTS layers on ac losses; (3) impact of the tape alignment on ac losses in each HTS layer; (4) influence of the thickness of HTS layers on ac losses; (5) effect of size and number of inter-tape gaps on ac losses; and (6) contribution frequency on the ac losses. The research results given in this paper are therefore not only valuable to suggest strategies for reducing ac loss in multi-layer cables but also for developing more accurate and effective methods to calculate ac loss in CORC HTS cables.

A High-Temperature Superconducting Wideband Bandpass Filter at the L Band for Radio Astronomy

In order to ensure the normal operation of radio astronomy observations, an extremely sensitive receiver system needs to be equipped in front of the large radio telescope. An 8-pole wideband high-temperature superconducting (HTS) filter using a Coplanar Spiral Resonator Structure with a passband of 1160∼1670 MHz is developed to suppress strong radio interference. The filter is fabricated on a 36 mm × 14 mm YBCO HTS film, which is deposited on a 0.5 mm thick MgO substrate. The minimum insertion loss measured in the liquid nitrogen temperature region is 0.03 dB, and the first parasitic passband appears at 2600 MHz. The measured results are in good agreement with the simulations. The filter can be used in radio telescope receivers for the observation of neutral hydrogen and pulsars, as well as in high-sensitivity satellite navigation instruments.

Influence of Interturn Contact Stress on the Quench Behavior of Insulated YBCO Pancake Magnets: A Study Based on Numerical Simulations

Insulated high temperature superconducting (HTS) magnets are still widely used in low field applications, such as HTS motors and generators. In this paper, a two-dimensional/three-dimensional (2D/3D) mixed electrothermal model and a homogeneous 3D electrothermal model are employed to study the influence of inter-turn contact stress on the minimum quench energy (MQE), longitudinal and transverse normal zone propagation velocity (NZPV) of insulated YBCO magnets for the temperature range 30 K – 60 K. This temperature range is of interest usually in applications, such as HTS motors, generators and transformers, because it allows the use of low cost cooling system. It is found that MQE increases significantly with increasing inter-turn contact stress. The inter-turn contact stress has small influence on the longitudinal NZPV of insulated YBCO pancake magnet. However, the transverse NZPV rises significantly with the increase of inter-turn contact stress. The transverse NZPV is nearly proportional to the inter-turn contact stress. The 3D homogeneous model gives results that are in agreement with those of 2D/3D mixed model, especially for the temperature range 45 K – 60 K; however, the MQE and transverse NZPV given by the two models are different for the temperature range 30 K – 45 K. That means for insulated HTS YBCO pancake magnets operating at the temperature range 45 K – 60 K, the 3D homogeneous electro-thermal model can be a good replacement of the 2D/3D mixed model to study the quench behavior, which can achieve better computational efficiency without significant loss of accuracy.

Исследование микротвердости композиционных материалов высокотемпературный сверхпроводник YBCO—нановолокна MoO3

В работе исследованы сверхпроводящие поликристаллические композиты YBa2Cu3O7-x + MoO3 с содержанием нановолокон MoO3 1, 5, 10, 15% (мас.). Из измерений электрического сопротивления определены температура и ширина перехода в сверхпроводящее состояние образцов с описанием вероятных механизмов наблюдаемых изменений. Из измерений микротвердости по Виккерсу определены модуль упругости, предел текучести, вязкость разрушения и индекс хрупкости. При исследованиях физико-механических свойств объемных образцов ВТСП содержащих MoO3, для интерпретации данных микроиндентирования и объяснения результатов с учетом эффекта размера вдавливания было использовано пять различных моделей.

Thermal and Electromagnetic Design of a Superconducting Coil

This article presents the methodology followed for the thermal and electromagnetic design of a superconducting coil at the University of Western Macedonia, Kozani, Greece, aimed to be used in a unique superconducting magnetic energy storage system for laboratory education and research purposes. First, we discuss the design constraints of the coil and select its dimensions using both the electromagnetic finite element method (FEM) and analytical equations based on the available length of a YBCO high-temperature superconductor. Then, we select the position of the coil inside a vacuum chamber. Then, an initial experiment without thermal load is performed to measure the cooling characteristics of the cryocooler. Using the results of the experiment and employing thermal FEM, we obtain an approximation of the cryocooler's cooling power versus time. After placing the coil and the thermal shield in the selected position inside the chamber, we carried out an experiment to measure the cooling curve with the load attached. The cryocooler's cooling power is approximated using the same FEM procedure. Thus, for this specific thermal load, the behavior of the apparatus is known. The methodology followed for the design of this unique system can be easily replicated by other researchers.

High-harmonic spectroscopy of quantum phase transitions in a high-Tc superconductor

We report on the nonlinear optical signatures of quantum phase transitions in the high-temperature superconductor YBCO, observed through high harmonic generation. While the linear optical response of the material is largely unchanged when cooling across the phase transitions, the nonlinear optical response sensitively imprints two critical points, one at the critical temperature of the cuprate with the exponential growth of the surface harmonic yield in the superconducting phase and another critical point, which marks the transition from strange metal to pseudogap phase. To reveal the underlying microscopic quantum dynamics, a strong-field quasi-Hubbard model was developed, which describes the measured optical response dependent on the formation of Cooper pairs. Further, the theory provides insight into the carrier scattering dynamics and allows us to differentiate between the superconducting, pseudogap, and strange metal phases. The direct connection between nonlinear optical response and microscopic dynamics provides a powerful methodology to study quantum phase transitions in correlated materials. Further implications are light wave control over intricate quantum phases, light-matter hybrids, and application for optical quantum computing.

Transformation from a high-temperature superconductor yttrium-barium-copper oxide to a photocatalytic material yttrium-barium oxide, a DFT-based investigation

Novel semiconductor photocatalysts are currently a hot research topic. We are inspired by the phenomenon that high-temperature superconductors can achieve superconductivity only under certain conditions (e.g., liquid nitrogen temperature). Here, based on the analysis of the energy band structure of the high-temperature superconductor YBCO (YBa2Cu3O7-x, YBCO), two new yttrium barium oxide (YBO) semiconductor materials, Y2Ba3O6 (YB3O) and Y2Ba4O7 (YB4O), are reported in this study. According to first-principles calculations, we find that YB4O and YB3O have stable formation energies, as well as forbidden band gaps, which are suitable for the visible light response. In addition, YB4O possesses a larger effective mass difference of carrier and stronger electron delocalization in various directions than that of YB3O, while YB3O possesses a larger light absorption threshold than that of YB4O. These two innovative yttrium-barium oxide materials show strong semiconducting properties and have great potential as photocatalysts.

Very Low-Noise Figure HTSC RF Front-End

A very low noise figure radio frequency (RF) front-end for the cellular realm is presented. The front-end is composed of two planar YBCO high critical temperature superconductor (HTSC) bandpass filters (BPFs) and a low temperature, low noise amplifier. Using advanced HTSC growth techniques, 8-pole hairpin BPFs are implemented in a YBCO thin film grown on both sides of a sapphire substrate. The front-end is designed and implemented based on the optimal configuration of the filters derived from advanced electromagnetic simulations. Measured performance at 77 K shows a high-frequency response and very low losses, with an insertion loss of 0.15 dB and a rejection ratio of −93 dBc. The integration of HTSC filters with the low noise amplifier results in a system with superior performance, with a low noise figure of around 0.5 dB. Low insertion loss and the compact dimensions of the filter, along with low total system noise, make the designed superconducting RF front-end highly attractive for radio receivers.

Electric-field noise in a high-temperature superconducting surface ion trap

Scaling up trapped-ion quantum computers requires new trap materials to be explored. Here we present experiments with a surface ion trap made from the high-temperature superconductor YBCO, a promising material for future trap designs. We show that voltage noise from superconducting electrode leads is negligible within the sensitivity ${S}_{V}=9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{2}/\mathrm{Hz}$ of our setup, and for lead dimensions typical for advanced trap designs. Furthermore, we investigate the frequency and temperature dependence of electric-field noise above a YBCO surface. We find a $1/f$ spectral dependence of the noise and a nontrivial temperature dependence, with a plateau in the noise stretching over roughly $60\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The onset of the plateau coincides with the superconducting transition, indicating a connection between the dominant noise and the YBCO trap material. We exclude the YBCO bulk as origin of the noise and suggest further experiments to decide between the two remaining options explaining the observed temperature dependence: noise screening within the superconducting phase, or surface noise activated by the YBCO bulk through some unknown mechanism.

High-density YBCO targets for sputtering with defect-free microstructure prepared by novel infiltration method

In this contribution, we demonstrate a new approach to the preparation of targets based on YBCO high-temperature superconductors, which are being used on large scale for thin-film superconductors deposition. The targets were manufactured by a new infiltration technique in a period of time less than 48 h. The phase composition of the final sample was analyzed by XRD, Rietveld refinement was used for the quantitative analysis. The microstructure of the final sample and the reference sample prepared by conventional target sintering was studied by SEM. The prepared target was also used for thin-film YBCO tape preparation by IJD in order to confirm the suitability of the novel technique. The prepared thin-layer was analyzed via XRD, SEM, EDS and optical microscopy. In addition, isothermal (T = 1250 K and T = 1325 K) isoactivity (pO2/p° = 0.21) sections of the Y-Ba-Cu-O phase diagram were calculated by FactSage program.

Influence of field-dependent critical current on harmonic AC loss analysis in HTS coils for superconducting transformers supplying non-linear loads

There are two main obstacles in front of the development of high temperature superconducting (HTS) technology for electric power network applications; tape price and cooling cost. In order to reduce cooling cost, it is vital to evaluate AC transport current loss of the tapes precisely and then reduce it by some design innovative approaches. In addition, AC transport current loss in HTS material is a critical design variable for large-scale power network applications such as HTS transformers, superconducting fault current limiters, and power cables, since they are continuously carrying the network/load current during their operating life. In existing power networks, harmonic production sources are commonly used and thus, currents are distorted. Therefore, the effect of nonsinusoidal current on the critical apparatus in the network such as transformer must be studied. In this paper, AC transport current loss of a single-turn 2G YBCO HTS coil was modeled and numerically calculated under nonsinusoidal transport current using finite element method. Furthermore, influence of dependency of critical current density to magnetic field on the AC transport current loss of HTS coil when carries distorted currents was considered. It was observed that nonsinusoidal current causes excessive losses in HTS coil. On the other hand, a case study on an HTS transformer supplying non-linear load was considered to study the loss increment as well as heat load change. It was observed that current harmonics increases the AC loss, and heat load of transformer and decreases the efficiency, consequently.

Balanced dual-band superconducting filter using square ring loaded resonators with ultra-low insertion loss and common-mode noise suppression

In this paper, a multi-mode square ring loaded resonator (SRLR) comprising a full-wavelength ring resonator and six open stubs is introduced. The resonant characteristics are discussed and analyzed using differential-mode (DM) and common-mode (CM) equivalent circuits. Compared to the conventional design, the proposed SRLR involves two advantageous modifications for high-order balanced structure. First, two pairs of open stubs on the four corners of the ring resonator provide more flexible control of the internal coupling between two SRLR units under DM excitation. In addition, the shorted H-shaped resonator is compact, which makes proposed structure suitable for high-order filter design with desired operating frequency and bandwidth. Second, one pair of open stubs is added to the ring resonator along the horizontally symmetric plane. We found that the proposed SRLR provides more design freedom for CM noise suppression without extra components or defected ground structure. In addition, the proposed SRLR topology structure is folded to avoid large circuit occupation. Based on our analyses, a fourth-order balanced dual-band bandpass filter was designed with two passbands operating at 2.2 GHz and 3.5 GHz with corresponding in-band insertion loss of 0.1 dB and 0.12 dB, respectively. The filter was fabricated using high-temperature superconductor (HTS) YBCO thin films on an MgO substrate. Good agreement between simulated and measured frequency responses was observed, which verifies the proposed structure and design method.

Design of special asymmetric cul-de-sac unit configuration high temperature superconductor filter with multi-pair of transmission zeros

A high-temperature superconductor (HTS) bandpass filter with special asymmetric cul-de-sac units (SACUs) is introduced and a compact low-radiating microstrip resonator is suggested for the filter realization. Such a filter is capable of providing better selectivity and higher out-of-band rejection and hence a decrease in adjacent-channel interference, which is of critical importance for mobile communication. This improvement of the filter characteristics results from an increase in the number of pairs of transmission zeros (TZs) on the imaginary axis on the complex plane when using the filter composed of the introduced SACUs, each providing a pair of TZs. An 11-pole filter consisting of two SACUs was fabricated using MgO substrate of 0.5 mm thickness with double-sided YBCO HTS film. Characterization of the filter at 77 K gave a central frequency of 2345 MHz, insertion loss 0.19 dB, an overall in-band return loss better than 15 dB, and an ultra-high band-edge steepness as a consequence of the two pairs of TZs. The measured characteristics are in good accord with those obtained by electromagnetic simulation.

Balanced Dual-Band Superconducting Filter Using Stepped-Impedance Resonators With High Band-to-Band Isolation and Wide Stopband

A balanced dual-band and wide-stopband high-temperature superconducting (HTS) bandpass filter (BPF) with deep stopband rejection is designed using modified stepped impedance resonators (SIRs) in this brief. The center frequencies of the two differential-mode (DM) passbands can be controlled by adjusting two electrical length ratios of the proposed SIR, while keeping the third spurious frequency far away for wide-stopband design. An inherent common-mode (CM) suppression can also be obtained due to the discriminating CM resonant frequencies different from the DM ones. Multiple transmission zeros (TZs) are achieved to realize high passband selectivity and enhanced DM stopband by multipath coupling and shunt stubs loaded on the I/O ports. The proposed balanced dual-band filter operating at 1.78/4.0 GHz is eventually fabricated using HTS YBCO thin films on a MgO substrate, which can significantly lower the insertion losses. The circuit was measured at the temperature of 77 K, which shows maximum insertion losses of 0.42/0.37 dB and a DM stopband of 5.0f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sup> with 40-dB attenuation, respectively.

Levitation Force Characteristics of High-Temperature Superconducting Bulks in a High Magnetic Field

The levitation force of high temperature superconducting (HTS) bulks can be enhanced by raising the strength of the external magnetic field. As to the field of HTS magnetic levitation (maglev), many researchers have also obtained this conclusion by levitation experiments above a permanent magnet guideway (PMG). However, the experimental results have limitations because the magnetic field above the PMG is relatively low, around 0.4 T at the 15 mm working height. In order to obtain more comprehensive levitation force characteristics of HTS bulks, it is necessary to carry out more experiments in high magnetic field. In this paper, the effects of magnetization angle and external field gradient on the levitation force of an HTS YBCO bulk which was manufactured with a top-seeded multi-seeded melt-textured process were studied. We set up a levitation force measurement system based on a 5-T Cryogen-Free Magnet (CRY-CFM-5 T-300-H3, Cryogenic Limited). The HTS bulk was cooled by liquid nitrogen in zero-field-cooling condition, and the external magnetic field was enhanced from 0 to 3 T. The HTS bulk was rotated 30° each time and finally rotated to 90°. Experiments show that the levitation force decreases from θ = 0° to 90°, where θ is the angle between the upper surface of the HTS bulk and the horizontal plane. The conclusion that the levitation force increases with the increase of the external magnetic field gradient in high magnetic field was also further confirmed.

Estimation of HTS electrodes properties for use in piezoelectric resonators

The microwave (MW) impedance of piezoelectric (PE) resonators with high-temperature superconducting (HTS) and with metal electrodes operating at a longitudinal acoustic waves (AW) frequency of ~2 GHz was modeled using Mason’s and the acoustic transmission line models. The MW impedances of the electrodes were also included into the model and the modeling parameters were chosen so as to be close to those of AlN (PE part of the resonator) and of HTS YBCO, Ag, and Pt (electrodes). It was shown that the limiting Q-factor value due to electric losses in the electrodes (computed under the assumption of small losses in the PE) is very high (~6×105) if even very thin (20 nm) HTS electrodes are used in the resonator at 77 K. The limiting Q-factor value is several thousand in the case of using similar metal electrodes. Thus, the HTS YBCO electrodes can be considered as attractive alternatives for application in PE resonators at low temperatures as they are characterized by low MW losses and affect weakly the resonance frequency.

Superfluid stiffness in cuprates: Effect of Mott transition and phase competition

Superfluid stiffness $\rho_s$ is a defining characteristic of the superconducting state, allowing phase coherence and supercurrent. It is accessible experimentally through the penetration depth. Coexistence of $d$-wave superconductivity with other phases in underdoped cuprates, such as antiferromagnetism (AF) or charge-density waves (CDW), may drastically alter $\rho_s$. To shed light on this physics, the zero-temperature value of $\rho_s=\rho_{zz}$ along the $c$-axis was computed for different values of Hubbard interaction $U$ and different sets of tight-binding parameters describing the high-temperature superconductors YBCO and NCCO. We used Cellular Dynamical Mean-Field Theory for the one-band Hubbard model with exact diagonalization as impurity solver and state-of-the-art bath parametrization. We conclude that Mott physics plays a dominant role in determining the superfluid stiffness on the hole-doped side of the phase diagram. On the electron-doped side, antiferromagnetism wins over superconductivity near half-filling. But upon approaching optimal electron-doping, homogeneous coexistence between superconductivity and antiferromagnetism causes the superfluid stiffness to drop sharply. Hence, on the electron-doped side, it is competition between antiferromagnetism and $d$-wave superconductivity that plays a dominant role in determining the value of $\rho_{zz}$ near half-filling. At large overdoping, $\rho_{zz}$ behaves in a more BCS-like manner in both the electron- and hole-doped cases. We comment on some qualitative implications of these results for the superconducting transition temperature.

Differential Dual-Band Superconducting Bandpass Filter Using Multimode Square Ring Loaded Resonators With Controllable Bandwidths

In this paper, a fourth-order dual-band high-temperature superconducting (HTS) differential bandpass filter (BPF) with controllable midband frequencies and bandwidths is developed by using modified multimode square ring loaded resonators (SRLRs). The differential-mode (DM) bisection and common-mode (CM) bisection of the modified SRLR are analyzed by using the even- and odd-mode method twice, and the corresponding resonant properties are obtained. With a proper design of the modified SRLR, two lowest DM resonances are chosen to construct two DM passbands with high in-band CM suppression. The DM resonances can be adjusted flexibly after adding tunable patches to the square ring. Meanwhile, the internal coupling between two modified SRLRs can be controlled separately by using two geometrical parameters. Consequently, the proposed dual-band BPF can achieve independent control of both the midband frequencies and the bandwidths of its two passbands. Moreover, a wideband CM suppression is realized by a combined use of an appropriately selected feeding structure and a frequency discrepancy technique. A fourth-order dual-band differential BPF is designed with two passbands operating at 2.325 and 4.900 GHz, respectively. The filter is fabricated using HTS YBCO thin films on a MgO substrate. Good agreement between the simulated and measured frequency responses are observed, verifying well the proposed structure and design method.

Multiscale Method for AC Loss Calculation of HTS Coated Conductors With Magnetic Substrate

The ac loss calculation problem is the key issue for a superconducting magnet. The existing numerical models do not consider the magnetic properties of the substrate while calculating the transport ac loss of high temperature superconductor (HTS) coated conductors. In fact, the unacceptable time and memory consumption makes the ac loss calculation a tough task while considering the magnetic properties of the substrate. This paper introduces a two-dimensional multiscale method for calculating the transport ac loss of HTS YBCO coated conductors with magnetic substrate, which can greatly reduce the calculation time under the premise of high accuracy. The multiscale method is realized with three unidirectionally coupled models and only considers the nonlinear E-J characteristics in two simple models with fewer degrees of freedom, which avoids considering the E-J characteristics in the whole coil. The calculation accuracy of the multiscale method is validated by comparing the simulation results with that of Ainslie's model with the same coil structure, which consists of 2 × 50 turns of YBCO tapes with ferromagnetic substrate. The results of the multiscale method model are highly consistent with that of Ainslie's model. The calculation speed can be increased by two orders of magnitude with the multiscale method, which indicates that this method is an effective approach to handle the transport ac loss calculation problems while including the ferromagnetic substrate. It also has the ability to solve much more complex problems in the future, such as large-scale HTS magnet.

Compact high temperature superconducting multi‐mode ultra‐wideband filter

AbstractA miniaturized high temperature superconducting (HTS) ultra‐wideband (UWB) bandpass filter (BPF) is presented based on stub‐loaded multi‐mode resonator (SLMMR) in this letter. This SLMMR constructed by loading three sets of different open stubs on a stepped‐impedance resonator brings five resonant modes into the passband for UWB bandwidth and a pair of transmission zeros in the transition bands for high selectivity. The filter is finally designed and fabricated on a 0.5‐mm thick MgO substrate with double‐sided YBCO HTS films. At 77 K, the measured results show that the 3‐dB bandwidth covers 3.0 GHz‐12.0 GHz; the minimum insertion loss is 0.11 dB; the return loss is better than 15.75 dB; the out‐of‐band rejection is greater than 24.35 dB in the lower stopband, and the upper stopband with 20 dB attenuation level is extended to 16.77 GHz.