HTSC Tapes Research Articles

Contactless verification of the defects in 2G HTSC tapes with two-side superconducting layers

Contactless verification of the defects in 2G HTSC tapes with two-side superconducting layers

Effect of the Rate of the Rise in Current on Transient Processes in a Superconducting Fault Current Limiter

The effect of the rate of the rise in the current to 1700 A/ms on the characteristics of a transition of units of superconducting (HTSC) modules from a superconducting to normal state has been experimentally studied. The units differed by the critical current of the HTSC tape and design. The units of HTSC modules are used as a part of the resistive superconducting fault current limiter (SFCL) for ac and dc grids. The obtained dependences should be taken into account when designing a resistive SFCL.

Current-carrying capability of GdBa2Cu3O7−x HTSC tapes in magnetic fields in the temperatute range of 2–100 K

The current-carrying capability of the second-generation HTSC tapes based on GdBa2Cu3O7−x (GdBCO), produced by the SuperOx Company by the pulsed laser deposition method is studied. Critical currents inmagnetic fields aremeasured by resistive andmagnetic (using a SQUID magnetometer) methods. The results obtained are compared with characteristics of an YBCO tape grown by chemical deposition (SuperPower, USA).

Analysis of normal zone propagation in superconducting tapes initiated by thermal disturbances

The normal zone formation in superconducting elements during the current flow is a dangerous process, which may lead to the irreversible destruction of materials. Results of the experimental and simulation studies of the normal zone propagation process in 1G (BSCCO) and 2G (ReBCO) superconducting tapes are presented in this paper. The obtained measurement and simulation results confirm the key role of the metallic shield of HTSC tapes in the heat transfer and the thermal stability.

On the use of the second-generation HTSC tapes in cryogenic transport systems for IFE targets

The results of experimental studies using SuperOx J-PI-12-20Ag-20Cu tape superconductors in developing capsule carriers for cryogenic systems of noncontact transport of targets for IFE are presented.

Hysteretic Magnetization Losses of HTSC Tapes in Coaxial AC and DC Magnetic Fields

In the work we present experimental results of ac magnetization losses measurements performed in the presence of a dc-bias magnetic field. Both ac and dc magnetic fields were coaxial and directed perpendicularly to the flat surface of sample tapes. The HTS tapes used in our experiments are commercially available composite tapes, namely a BSCCO-2223/Ag multifilamentary tape and an YBCO-123 coated conductor tape. The measurements were carried out with a sinusoidally varying magnetic fields at frequency range of about 21-113 Hz, and amplitudes up to 100 mT. The superimposed a dc-bias magnetic field was of the order of up to 50 mT. At a certain magnetic field amplitude, and at a certain dc bias magnetic field, a distinguish minimum in ac losses is observed. Occurrence of the ac loss minima differs considerably for two studied sample tapes.

Magnetic Properties of the Stack of HTSC Tapes in a Wide Temperature Range

The trapped field strength of HTSC stacks were measured in the temperature range T=4-80K and dc magnetic fields up to 8 Т. A single 12mm by 12mm square samples were cut from commercial (RE)BCO tape 12mm wide and then stacked together. The number of layers in the stacks was varied from n=5 to n=250. Trapped field strength was measured by means of Hall probe which was placed directly on the stacks surface. The dependences of remnant field strength Brem on number of layers in the stacks at different temperature Brem (n) as well as on temperature dependences Brem (T) at various n were obtained. It was found that Brem (n) dependences have a nonlinear character with a tendency to saturation for n > 60. The maximum remnant (trapped) field was found to be more than 2.5 Т at T=4 К. The relaxation of trapped field was studied also and it was determined that the rate of relaxation processes tends to decrease with the increase in a number of tapes in the stack. The correlation between dependency Brem (n) and dependency of magnetic levitation force measured at T=77K at zero field cooling were found.

Magnetic-field dependence of the local critical current density in the second-generation HTSC tapes

An experimental-computational algorithm of precisely determining the dependence of the local critical current density in a superconducting film on the local magnetic field is developed. The determination is performed proceeding from the dependence of the transport critical current through a wide superconducting tape on the external magnetic field. It is shown that the existing formulas approximating this dependence do not allow the solution of this problem with an accuracy provided by modern experimental techniques. To provide a necessary accuracy of the solution, a four-parametric approximation formula is proposed and the parameters of this dependence are determined by the example of the second-generation HTSC tape.

Investigation into the critical current of second-generation wire-tapes based on the GdBa2Cu3O7 (GdBCO) high-temperature superconductor fabricated by pulsed laser deposition

The results of measurements of the functional characteristics of 2G HTSC wires produced by SuperOx-Japan using pulsed laser deposition are given. Our investigations show that the HTSC tape fabricated by pulsed laser deposition is practically not worse than the HTSC tape fabricated by chemical vapor deposition (SuperPower, United States) in its current-carrying characteristics in an external magnetic field.

The shock‐wave application for increasing of a critical current in composite HTSC

AbstractThis paper aims to find methods for effective pinning centres generation using shock waves in order to increase the current‐carrying capability of high temperature superconductors in high magnetic fields. It presents the results of the effect of a shock wave on properties of composite high temperature superconductor tapes (HTSC): YBCO(123) and Bi(2223). To generate the shock wave, authors used the interaction of a solid state target with a high speed cumulative plasma jet generated in a Plasma Focus setup. Shock waves have a front‐edge pressure of 1011 Pa. The sample was exposed to the plasma pulse for about 50 ns. A significant and lasting increase of the critical current density of composite HTSC tapes was observed as a result of the effect of shock waves, also in high magnetic fields. This paper discusses the presumed reasons for the increase of the critical current. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Temperature Rise of Copper and HTSC Tapes in Liquid Nitrogen by a Step-wise Current Pulse

Abstract Features of a heat transfer to liquid nitrogen from copper or superconducting tapes loaded by a short step-like current pulse have been studied experimentally. The delay of a heat transfer development have been observed and studied. A phenomenological model enabling us to describe qualitatively the non-stationary heat transfer process on the basis of the stationary boiling curve is proposed.

Influence of Shear Stress on Current Carrying Capabilities of High Temperature Superconductor Tapes

To achieve high currents single HTSC tapes or Roeble strands must be combined into a cable. Many concepts like Rutherford cable, coated cable in conduit or full size cable model of Roebel strands require twisting of the HTSC tapes. Twisting or torsion exerts longitudinal and shear stress on the tapes which degrade the current carrying capabilities. Finite element analysis was done to explain this behavior. However, the influence of longitudinal stress in HTSC tapes on critical current is well documented, but there is no experimental data for pure shear stress available. To verify the finite element analysis shear stress experiments are of significant interest. With a three point bending method shear stress can be applied to a single HTSC tape. Critical current measurements with varying shear stress are conducted for several HTSC tapes. With the experimental results and the longitudinal stress dependence a correlation between torsion experiments and finite element analysis is possible.

Finite Element Analysis of Torsion Experiments on HTSC Tapes

During the past years the application of 2G HTSC material is growing. However, to achieve high currents single HTSC tapes must assembled in a Roebel-cable geometry. Going to even larger cable concepts like Rutherford cables, twisting of HTSC tapes is required. To examine the influence of twisting or torsion on critical current of Coated Conductor tapes or Roebel strands, systematic experiments were carried out giving results for critical twisting lengths. The results have to be examined considering the different strain states within the tape under torsion. On one hand longitudinal strain plays a role, but on the other hand shear strain has to be addressed also. To understand these results theoretical assessment of the stress strain situation within the tape under torsion was performed. Together with finite element analysis the effect of longitudinal and shear strain was systematically examined to give an understanding of the critical current behavior under torsion.

Application of shock waves for the improvement of current-carrying properties of YBCO(123) and Bi(2223) HTSC tapes in magnetic fields

Shock waves with a leading-edge pressure of ∼1011 Pa, which were produced in a plasma focus setup, were used to increase the critical current density in YBCO(123) and Bi(2223) HTSC tapes. It was shown that the effect of chemically inactive high-temperature high-density plasma on the HTSC tapes leads to an irreversible increase in the critical current in high magnetic fields. The improvement of the current-carrying properties of the YBCO(123) HTSC tape is confirmed also by the results of scanning Hall magnetometry at 77 K. In particular, in a field of 8 T applied perpendicular to the c axis (H ⊥ c), the increase in the critical current after shock-wave treatment is ∼60%. In the case of the Bi(2223) tape, the critical current in a zero field in the sample portion subjected to shock-wave action was found to be twice as high as that in the untreated portion (100 and 50 A, respectively). The increase in the critical current can be related to a number of possible structural transformations of the superconducting core. First of all, an increase in the density of current-carrying core, which leads to an increase in weak bonds at grain boundaries, is possible. In this case, the formation of nanosized defects, which are responsible for an increase in the force of pinning of Abrikosov vortices, is also possible.

Current distribution in HTSC tapes obtained by inverse problem calculation

The development of SC devices based on HTSC tapes requires a deep knowledge of the current distribution in both pre-saturation and post-saturation regimes. Magnetic measurements have shown the possibilities to derive the current distribution by Inverse Problem Solution in finite sized bulks, based on a non destructive measurement of the magnetic field created by the own current flowing in the SC. In this work, the QR inversion strategy is extended to non finite systems by considering the effect of the boundaries. We present a method to derive the current distribution in a cross-section of a tape based on Hall magnetic mapping by using a specifically designed inverse problem solver. This method is applied to a series of Hall measurements corresponding to a full magnetization cycle of a commercial tape, produced by applying a set of the currents applied to the tape of several intensities. Details of the experiments and the calculation method are reported and the applicability as homogeneity test and losses studies is discussed.

Measurement of AC Profiles of Magnetic Field Above HTSc Tape Using Hall Probe Technique With Help of DAQ Cards and Triggering

Power applications of superconductors, such as transformers, power cables, motors, and generators require the study of the influence of AC magnetic fields on properties of high-temperature superconductors. Our contribution comprises a convenient method for a measurement of components of magnetic fields generated by induced currents circulating in a HTSc sample located in an AC magnetic field. Also, a data acquisition system is presented that allows for the measurement of signal proportional to the position and to the component of magnetic flux density by a Hall probe at a defined level of an applied magnetic field in each period simultaneously with the help of triggering. This differential Hall measurement enables us to acquire magnetic field profiles or maps in the vicinity of the sample corresponding to a certain value of the magnetic field applied. It is possible to obtain results for any value of the magnetic field applied in the course of the period, i.e. from zero up to a maximum value of the magnetic field at the rising or falling slopes according to trigger conditions. In particular, it can be used to investigate the current distribution in the sample during the AC cycle or defect detection in HTSc tapes.

Anisotropic characteristics of the energy dissipation in Bi(2223) ceramics and tapes in weak magnetic fields

For practical application of HTSC tapes as current leads, their behavior in realistic conditions, in the presence of magnetic field, becomes crucially important. We have investigated in detail the resistivity transition and the excess resistivity induced by low magnetic fields (1–750 Oe) in highly aligned composite structures of Bi(2223) based tapes and also, for comparison, in bulk ceramics of the same composition. We demonstrate the strong dependence of the electrical and magnetic properties on the microstructure of the composite ceramics. We observed also a dependence of the energy dissipation on the direction of the transport current with respect to the grain orientation. Percolation theory and the effective medium approximation are applied to analyze the anisotropy in the resistive transition of these systems.

Solidification of nitrogen refrigerant and its effect on thermal stability of HTSC tape

We investigated the effect of solidified nitrogen refrigerant upon the thermal stability of HTSC tape. Solid nitrogen was produced by two methods, one by conduction cooling at a very slow cooling rate and another by evacuating the vapor. It was shown experimentally that the thermal stability of HTSC tape is improved drastically when it is impregnated with solid nitrogen produced by the conduction cooling. Furthermore, so-called dry-out phenomenon was dominated by the cumulative energy of the thermal disturbance by the heater.

Transverse resistivities in untwisted HTSC tapes at 4.2, 30, and 60 K

Using vibrating sample magnetometry eddy-current loss was measured on unbridged Bi:2223/Ag tapes. After taking the tape's aspect ratio, a/ b, into account the transverse resistivity, ρ ⊥, obtained was still very much greater than that obtained using the effective-medium prescription, in this case (1+ λ)/(1− λ) ρ Ag,bulk at 4.2 K. Moreover, ρ ⊥ was found to be proportional to a/ b. Temperature dependence measurements verified that the apparently enhanced resistivity was seated within the interfilamentary matrix, and not asssociated with any T- and H-independent filament/matrix barrier. It was concluded that the eddy-current loss was occurring within a relatively small volume fraction of the filamentary region and that appropriate volume normalization would in fact return a ρ ⊥ closer to expectation. This has important implications in terms of low AC-loss strand design. The above results were based on 4.2 and 30 K measurements. At 60 K where intrafilament flux flow might be expected especially at higher fields, the apparently large ρ ⊥ becomes further enhanced by an additional resistivity component. This is a dynamic resistance that the d H/d t-driven eddy-currents encounter as they circulate along the filamentary segment of their path under flux flow.

AC losses in transport current regime in applied AC magnetic field: experimental analysis and modeling [superconducting cables

Bi-2223 silver sheathed tapes are currently used in prototypes of HTSC power devices, where they generally carry an electrical AC current and are exposed to an alternating magnetic field that may have different orientation with respect to the tape. In this work, the authors describe the experimental set-up for measuring AC losses of HTSC tapes due to the simultaneous presence of AC current and AC magnetic field. The experimental results have been compared and contrasted with a numerical model purposely developed for the evaluation of current distribution and AC loss in HTSC tapes.