Type High-temperature Superconductor Research Articles

Research on Force Characteristics and Running Performance of Novel Type High-Temperature Superconductor Magnetic Levitation Vehicle

Research on Force Characteristics and Running Performance of Novel Type High-Temperature Superconductor Magnetic Levitation Vehicle

Improvement of trapped magnetic field in GdBCO by waveform control pulse magnetization at 70 K

We attempted to trap a strong magnetic field with a single pulsed magnetic field by applying waveform control pulse magnetization (WCPM) method to a high-temperature superconductor (HTS) bulk sandwiched between two vortex-type copper coils at less than 77 K. The GM cryocooler conductively cooled the GdBCO bulk to 70 K in an arrangement similar to the internal structure of our axial gap type HTS motor. The HTS bulk showed no flux jump, while the duty ratio of WCPM was small. When we increased the duty ratio, we found a flux jump without looking at any prior signs and the trapped magnetic flux density increased twice. Hence we attempted a negative feedback WCPM with the control target at the highest trapped magnetic flux density while no flux jump was found. After trial and error of control conditions, the HTS bulk sample trapped a maximum magnetic flux density of 1.79 T by a single pulse magnetic field. If the WCPM technique is used, a single pulse magnetic field will cause the HTS bulk to obtain a higher trapped field at lower temperatures.

The step-edge type HTS rf SQUID coupling with a LC circuit in ultra-low field NMR system

The step-edge type high temperature superconductor (HTS) radio frequency (rf) superconducting quantum interference devices (SQUIDs) were fabricated from YBa2Cu3O7−δ thin films with a field sensitivity of 66 fT/Hz1/2. Even though the sensitivity of the rf SQUID sensor used in the experiments was degraded to 77 fT/Hz1/2 in the magnetic shielded room (MSR), the performance of the rf SQUID sensor was good enough for the ultra-low field (ULF) nuclear magnetic resonance (NMR) experiments at a measurement field of 61.5 μT. With the help of a strictly controlled fast switching circuit and a coupled LC circuit which acted as flux transformer, the signal-to-noise ratio (SNR) of the rf SQUID-based ULF NMR system with different operating points was measured. The optimum SNR was 40 dB which increased significantly by coupling an input coil closely beneath the rf SQUID sensor. The extracted 1/T1 value for pure water sample at 23 ∘C showed the rf SQUID based ULF NMR was an effective system for ULF NMR researches. All above, the direct coupled method and the control circuit show a great potential in the future rf SQUID-based ULF NMR &MRI system.

The Born–Mayer–Huggins potential in high temperature superconductors

The Born–Mayer–Huggins potential which has been found the best suitable potential to study the YBa2Cu3O[Formula: see text] type high temperature superconductors is revisited in a new framework. A deeper insight in it reveals that the Born–Mayer parameters for different interactions in high temperature superconductor are not simple quantities but several thermodynamic and spatial functions enter the problem. Based on the new theory, the expressions for pressure, bulk modulus and Born–Mayer parameters have been derived and it is established that these quantities depend upon Gruneisen parameter which is the measure of the strength of anharmonic effects in high temperature superconductors. This theory has been applied to a specific model YBa2Cu3O[Formula: see text] crystal for the purpose of numerical estimates to justify the new results.

Fractal dimension of structural inhomogeneities in granular YBCO superconductor in magnetic field

The influence of a fractal character of the structure of an YBCO type high-temperature superconductor on its current-voltage characteristic in a magnetic field has been studied. The fractal dimension and connectivity index of vortex transport channels are determined as functions of the magnetic field strength. It is established that the glassy state index corresponds to that of a vortex glass.

Influence analysis of structural parameters on electromagnetic properties of HTS linear induction motor

A new type high temperature superconductor linear induction motor is designed and analyzed as a prototype to ensure applicability aimed at industrial motors. Made of Bi-2223/Ag, primary windings are distributed with the double-layer concentrated structure. The motor is analyzed by 2D electromagnetic Finite Element Method to get magnetic field distribution, thrust force, vertical force and so on. The critical current of motor and the electromagnetic force are mostly decided by the leakage flux density of primary slot and by the main magnetic flux and eddy current respectively. The structural parameters of motor have a great influence on the distribution of magnetic field. Under constant currents, the properties of motor are analyzed with different slot widths, slot heights and winding turns. The properties of motor, such as the maximum slot leakage flux density, motor thrust and motor vertical force, are analyzed with different structural parameters.

Simulation of electrical, magnetic and thermal properties of inductive fault current limiters made of YBCO ceramic superconductors

The fault current limiter (FCL) is a device capable of limiting currents in electrical networks during fault conditions. In this device, the acting element is a high temperature superconductor (HTS) ring made of ceramic material. The inductive FCL consists of a primary normal metal coil coupled via a ferromagnetic core to a secondary short-circuited superconducting coil assembled in the form of a set of HTS rings or cylinders. In the normal conditions of the protected circuit, the superconducting rings are in the superconducting state. Under fault conditions, the secondary superconducting coil becomes resistive. As a result, in normal operation, the impedance of the FCL is much less, while in the current limiting mode, the impedance is higher than the impedance of the network. A 12 kVA inductive closed core type HTS FCL with melt textured YBCO ring was developed and tested. The current limiting properties of the FCL were investigated experimentally and the results were compared with those of computer modeling. The quench behavior of the YBCO HTS ring has strong influence on the current limiting properties of the FCL. For the description of transient and quasi-stationary processes of the FCL, the authors have developed a model and a numerical simulation, which consist of coupled electromagnetic and thermal processes, can handle the influence of the hot-spots generated in the HTS, and the non-linear characteristics of the magnetic core. The model provides the various operational modes of the FCL due to material properties observed in the experiments, and enables the determination of main dimensions of the device including those of the magnetic circuit. Due to the very good agreement between the experimental and calculated results, the model can directly be used for the engineering design of inductive type HTS fault current limiters.

High-pressure–high-temperature-induced variations in Y123-structural type superconductors

The peculiarities of structure, superconductive (SC) and mechanical properties variations of melt-textured Y, Nd, (Y,Nd)-123-based and Y,Sm-123-based with additions of Ag high-temperature superconductors (HTS) vs. high-pressure (2–5 GPa)–high-temperature (750–1500°C)-time (10–30 min) treatment conditions are presented. The process of high-pressure–high-temperature (HP–HT) sintering of SC YBa 2Cu 3O 7− δ ceramics from YBa 2Cu 3O 7− δ powder is also discussed. The HP–HT treatment and sintering enable us to manufacture practically poreless HTS with improved mechanical characteristics for a short time. High pressure heating allows the superconductive characteristics of investigated Y-123 structural type HTS to be preserved or increased.

Ion Beam Modification of TI-Ba-Ca-Cu-O Type High Temperature Superconductors During Irradiation

AbstractMicrostructural modification of high temperature superconductor (HTS) single-crystal plates of T1-1212 and T1-2212 (numbers designate the Tl/Ba/Ca/Cu cation ratio) was studied during 1.5 MeV Kr+ and Xe+ ion irradiation with in-situ electron diffraction and after ion irradiation with high resolution TEM (HRTEM). Similar in-situ temperature dependence effects are seen for both phases. During irradiations from 22K to 673K, an amorphous halo develops after very low ion dose or fluence (l.7X1012 ions/cm2). During irradiation at 100K and 300K, complete amorphization is obtained, while at 22K and ≥533K, the halo fades slightly and a polycrystalline ring pattern develops, indicating ion irradiation induced crystallization occurred. After a low ion dose (8.5XlO12ions/cm2) at 100K and 300K, HRTEM reveals amorphous regions 5 -20 nm in size which are not columnar and do not all penetrate the entire sample thickness. At 22K and ≥533K, Moire fringes and misoriented crystallites of cascade size are observed. The 4 - 6nm crystallites are thallium-rich.

Comparative Mössbauer study of EuBa2 (Cu1-x 57Fe x )3O7-d and EuBa2Cu1-x 57Fe x )4O8 superconductors

Structural differences between the 1-2-3 type and 1-2-4 type high temperature superconductors were studied by comparing their151Eu and57Fe Mossbauer spectra. The similarities between the corresponding Mossbauer parameters of Eu Mossbauer spectra of 1-2-3 and 1-2-4 compounds demonstrate that the Eu state can be considered to be identical in both perovskites. The changes in the Fe Mossbauer parameters of 1-2-4 type superconductor compared to those of 1-2-3 type compound can be associated with structural differences.

Reduction of the zero-phonon 57Fe Mössbauer fraction just above Tc in the (Bi,Pb)2Sr2Ca2Cu3O10 superconductor.

A decrease of the zero-phonon fraction of the $^{57}\mathrm{Fe}$ M\"ossbauer absorption was observed in the temperature range 93--120 K in an Fe-doped (Bi,Pb${)}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$-type high-temperature superconductor indicating an anomalous behavior of the lattice vibrations. The isomer shift changes slightly in the same temperature range. The absence of a Goldanskii-Karyagin effect shows that the Fe mean-square displacement is isotropic. Between 150 and 550 K, the temperature dependence of the zero-phonon fraction follows a Debye model with a M\"ossbauer Debye temperature of 350 \ifmmode\pm\else\textpm\fi{}20 K.

Transport critical current in rare-earth-substituted superconductors RBa

We have measured the transport critical current densities (J/sub c/) of various bulk polycrystalline RBa/sub 2/Cu/sub 3/O/sub 7/..sqrt../sub delta/-type high-temperature superconductors (R = Gd,Dy,Sm,Ho,Y) at 77 K as a function of magnetic field. The substitution of yttrium with magnetic rare-earth elements resulted in no appreciable improvement or deterioration in the transport J/sub c/ values (typically in the range 200--600 Acm/sup 2/ at H = 0). The similar J/sub c/ values of all five barium cuprate compounds and their rapid deterioration in weak magnetic fields in a similar manner (J/sub c/<10 Acm/sup 2/ at H = 1000 gauss) suggest the possibility of generic ''weak link'' problems in these compounds