Bi2Sr2Ca2Cu3Ox Tapes Research Articles

Analysis of critical current and hot spot behavior in Bi-2223 stacked-tape cable for fusion reactor

The cable-in-conduit-conductor (CICC) based on Bi2Sr2Ca2Cu3Ox (Bi-2223) tape has potential to be used in fusion magnets duo to its high current-carrying capacity under high field and low temperature. In this study, the optimized study on the stacked tape cable based on Bi-2223 tape was performed. The effect of the quantity of grooves and tapes on the critical current is studied by the finite element method, respectively. The comparison between the copper and aluminum frame on the quench behavior of cable is also discussed. The results shows that the critical current of cable is mainly determined by the quantity of tape in cable where the self-field effect has little impact on the critical current in 4.2 K and 15 T. The minimum quench energy (MQE) is proportional to the tape numbers where the MQE with copper frame is higher than that with aluminum frame. The hot spot temperature is decreased with tape numbers for cable with aluminum frame, however, the effect of tape numbers on the hot spot temperature of cable with copper frame is not obvious where the quench is triggered by MQE. Moreover, the cable with lower quantity of grooves shows higher stability compared with other variants containing the same number of tapes.

A 40-mm High-Temperature Superconducting Surface Resonator in a 3-T MRI System: Simulations and Measurements

In this paper, the Ansoft high-frequency structure simulation (HFSS) was adapted to investigate the unloaded quality-factor value of the radio-frequency (RF) receiving resonator. This paper focused on the materials aspects, and a comparison between electromagnetic stimulations and measurement was conducted. A 40 mm in diameter Bi2Sr2Ca2Cu3Ox (Bi-2223) tape high-Tc superconducting RF resonator in 3 T was stimulated and built. The simulation models were established according to the experimental dimension of the Bi-2223 surface resonator. Measurements show that the Bi-2223 surface resonator at 77 K provides a gain of 3.84-fold signal-to-noise ratio on phantom images over that of the homemade copper resonator at 300 K. Measuring results were in accordance with predicted ones, and the difference between the predicted SNR gains and measured SNR gains is 1%. This paper suggests that using a Bi-2223 surface resonator at 77 K could be more useful for magnetic resonance imaging coils than a copper surface resonator at 300 K.

Using high-Tc superconducting resonator for enhancement of diffusion tensor imaging

Here, a report on diffusion tensor imaging (DTI) using a 125.3 MHz high-temperature superconducting (HTS) surface resonator for magnetic resonance imaging (MRI) is presented. A 40 mm in diameter Bi2Sr2Ca2Cu3Ox (Bi-2223) tape surface resonator was built. Using a HTS surface resonator at 77 K than a similar copper surface resonator at 300 K, the capacity to save the accuracy of DTI in a reduced scan time (11 min) was demonstrated. The standard deviation of deviation angles of DTI fiber tracking was also improved by 2.5 gains. The use of HTS surface resonator may improve the reliability of fiber tracking experiments.

Human hand imaging using a 20 cm high-temperature superconducting coil in a 3T magnetic resonance imaging system

A high-temperature superconducting (HTS) radio-frequency (rf) coil has been proposed as a promising tool in the investigation of tissue microscopy with high resolution due to its low-resistant characteristic for magnetic resonance (MR) probe design. In this work, a 200 mm in diameter Bi2Sr2Ca2Cu3Ox (Bi-2223) tape HTS rf coil was built; and a signal-to-noise ratio (SNR) with the HTS tape coil having 2.22 folds higher than that of a home-made copper coil for a phantom MR study was demonstrated. Testing results were in agreement with predicted ones, and the difference between the predicted SNR gains and measured SNR gains is 0.9%. Using in vivo imaging, a SNR with the HTS tape coil having 1.95 folds higher than that of a home-made copper coil for a human hand MR study was presented. The HTS coil is expected to generate a higher SNR gain after optimization. Further applications of a functional magnetic resonance imaging system are under investigation to test the applicability of this HTS coil system in a 3T system.

Study of grain boundary properties in Ag-clad Bi2Sr2Ca2Cu3Ox tapes by multi-phase electron backscatter diffraction analysis

The properties of grain boundaries within Ag-clad (Pb,Bi)2Sr2Ca2Cu3Ox (Bi-2223) tapes are studied by means of electron backscatter diffraction (EBSD). The achieved high image quality of the Kikuchi patterns enables multi-phase EBSD scans including Bi-2223, Bi2Sr2CaCu2Ox (Bi-2212), Bi2Sr2CuOx (Bi-2201), (Sr,Ca)14Cu24O41 and Ag to be performed. For the EBSD scans a maximum spatial resolution of 30 nm was reached enabling a detailed orientation analysis. The nature of the grain boundaries is discussed on the base of the EBSD data. While the main orientation of the tape is in [0 0 1] direction, a large number of misorientations is detected. These misorientations are visualized using crystal direction (CD) maps. Furthermore, EBSD enables the spatially resolved mapping of the misorientation angles within each phase separately. The influence of these grain boundaries on the current transport properties is discussed.

Effect of tensile strain on grain connectivity and flux pinning in Bi2Sr2Ca2Cu3Ox tapes

The grain-to-grain connectivity in Bi2Sr2Ca2Cu3Ox tapes is still poorly understood, even though they have been commercially available in long lengths for several years. This letter explains the effects of tensile strain on the grain-to-grain connectivity in Bi2Sr2Ca2Cu3Ox tapes. The different length scales at which damage to the grain structure occurs are studied with magneto-optical imaging, scanning-electron microscopy, and transport current. These data show that the initial degradation in critical current when strain exceeds the irreversible strain limit is caused by microcracks (∼100–500nm in width) that form mainly at high-angle grain boundaries. Filament-wide cracks (∼5–10μm in width) form at locations of lower grain density in the filaments at strains far exceeding the irreversible strain limit. However, in contrast to previous reports, a careful analysis of the pinning force as a function of tensile strain, taking into account current sharing with the normal matrix by using the offset criterion, shows that intragranular flux pinning is not affected by strain in any significant way.

Shielding effect of an open-type hybrid magnetic shield with high-Tc superconducting loops

Double-D-shaped high-Tc superconducting loops were used to form an open-ended, cylindrical magnetic shield for biomagnetic measurements. The total magnetic flux through such a superconducting loop stays constant; thus, the loop can shield a cylindrical magnetic shield from an external magnetic field that penetrates into it from its open ends. The high-Tc superconducting loops are made of Bi2Sr2Ca2Cu3Ox tape wire, and the cylindrical magnetic shield is made of flexible magnetic sheets composed of Fe–Cu–Nb–Si–B nanocrystalline alloy. Both axial and transverse magnetic field noise in the shield were measured with high-Tc superconducting quantum interference devices. These measurements indicate that the double-D-shaped high-Tc superconducting loops at each open end of a cylindrical magnetic shield reduce not only axial but also transverse magnetic field noise in the magnetic shield.

Open-type hybrid magnetic shield using high-TC superconducting wire and flexible magnetic sheets

An open-ended, cylindrical magnetic shield using high-TC superconducting rings and flexible magnetic sheets has been developed. The superconducting ring is made of Bi2Sr2Ca2Cu3Ox tape wire, and the flexible magnetic sheet is made of Fe–Cu–Nb–Si–B nanocrystalline alloy, which has superior soft magnetic properties. The superconducting rings are set near the open ends of a ferromagnetic cylinder. When a magnetic field is induced in the rings, a shielding current flows so as to keep the magnetic flux through the ring constant. It is concluded that the superconducting rings effectively increase the shielding factor of a magnetic shield.

Transverse compressive stress effects on the critical current of Bi-2223/Ag tapes reinforced with pure Ag and oxide-dispersion-strengthened Ag

We have measured the effect of transverse compressive stress on the critical current of two similar sets of Bi2Sr2Ca2Cu3Ox (Bi-2223) tapes in a direct comparison between tapes reinforced with pure Ag and oxide-dispersion-strengthened (ODS) Ag. The critical-current degradation at a transverse stress of 100 MPa was about 10% for the Bi-2223/pure Ag tapes and only about 3% for the ODS Ag tapes. In one case for each sample type the degradation was significantly greater, and there was an apparent correlation with porosity in the superconductor filaments. The degradation was the same for critical-current criteria from 5 μV/cm down to 0.1 μV/cm.

Enhancement of transport critical current densities in Bi2Sr2Ca2Cu3Ox tapes by fission tracks

Bi 2 Sr 2 Ca 2 Cu 3 O x (Bi-2223) tapes were processed by the standard powder-in-tube technique, but small amounts of UO4 were added prior to processing. Both U-doped and undoped tapes were subsequently exposed to a reactor spectrum of neutrons. Whereas the undoped materials show moderate enhancements of the critical current densities Jc due to the pinning action of the fast-neutron-induced collision cascades, Jc in the U-doped tapes increases by factors of 10–20 due to thermal-neutron-induced fission of 235U and the subsequent formation of fission tracks. Since the enhancements are particularly pronounced, when the magnetic field is applied perpendicular to the tape surface, the characteristic Jc anisotropy is strongly reduced in a certain field range. At the same time, the irreversibility field at 77 K is doubled for both field orientations.

The local variation of Ca2PbO4 in the core of (Pb,Bi)2Sr2Ca2Cu3Ox superconducting tapes during thermal processing with different heating rates

We present the results of an investigation into the variation in the amount of the secondary phase, Ca2PbO4, during the thermal processing of silver-sheathed (Pb,Bi)2Sr2Ca2Cu3Ox tapes. It has been found that, after an initial fast decrease in Ca2PbO4, there is an incubation period, of 20 hours for heating rate 2°C/hr and 30 hours for heating rate of 60°C/hr, during which the amounts of both (Pb,Bi)2223 and Ca2PbO4 remain unchanged. After this period the amount of Ca2PbO4 phase decreases simultaneously with the increase of (Pb,Bi)2223 phase.

Evidence that pair breaking at the grain boundaries of Bi2Sr2Ca2Cu3Ox tapes determines the critical current density above 10 K in high magnetic fields

The critical current density of an aligned Ag doped Bi2Sr2Ca2Cu3Ox tape has been measured from 10 K up to Tc (105 K) in magnetic fields up to 15 T. Measurements of the critical current density (Jc,(B, T)) have been completed for three different configurations of magnetic field, transport current, and superconducting tape: (i) J perpendicular to c axis, J perpendicular to B, and B perpendicular to c axis; (ii) J perpendicular to c axis, J perpendicular to B, and B//c axis; (iii) J perpendicular to c axis, J//B, and B perpendicular to c axis. In all three configurations at high magnetic fields up to 15 T, we find the critical current density can be described by Jc(B, T)= alpha ( phi , T) exp(- mu 0H/ beta ( phi , T)) where ( beta phi , T) is of a separable variable form beta ( phi , T)= beta /sup /(T)/f( phi ) where beta /sup /(T) is a function of temperature alone and f( phi ) is a constant dependent only on the orientation of B, J, and the c axis. A similar but not identical exponential magnetic field dependence has been found in Bi2Sr2Ca2Cu3Ox, Bi2Sr2CaCu2Ox and YBa2Cu3Ox, thin films. We discuss the evidence that the exponential magnetic field dependence suggests that a pair breaking mechanism operates at barriers in these materials. We conclude that the grain boundaries determine Jc(B, T) in the Bi2Sr2Ca2Cu3Ox textured tape.