D. Miyagi

Characteristics of AC transport current losses in YBCO coated conductors and their dependence on distributions of critical current density in the conductors

We measured AC transport current losses in two kinds of thin film YBCO coated conductors with different critical current densities. The results show that the loss characteristics do not follow the Norris strip model. The loss in one of the samples follows the Norris elliptical model and the loss data of the other sample fall in between the elliptical and strip models. It is considered that the loss in a YBCO conductor of high quality, that is, high critical current density, follows the strip model. However, the measured losses of even high critical current density conductor (J/sub c/ /spl ap/ 10/sup 6/ A/cm/sup 2/) does not follow the strip models. In the paper, an analytical model is presented to describe the AC transport current loss characteristics more generally than the Norris models and the model can well describe the experimental results.

Study of frequency dependence of AC transport current losses in HTS conductors subject to DC background field

To study a mechanism of AC transport current losses in HTS wires, the authors measured the AC transport current losses of two kinds of HTS wires subject to DC background magnetic field by changing frequency of currents. The tested wires are a multifilamentary Bi2223/Ag sheathed tape and YBCO thin film conductors. The measurement results show that the losses in the Bi/Ag sheathed tape and YBCO conductors deviate from the Norris model in different ways and are only weakly dependent on frequencies of transport currents. In this paper, measured results are presented and the loss characteristics are explained based on a numerical model which they made in a previous work to analyze the AC transport current losses.

Study on relation between AC characteristics and critical current distribution in YBCO tape

We measured AC transport current loss of a high current density YBCO tape conductor. The tape conductor was made by depositing YBCO thin layer of /spl sim/1 /spl mu/m thick on a LaAlO/sub 3/ single crystal substrate and its critical current was around 100 A at 0 T and 77 K. The loss data deviated from the Norris curves for the elliptical and strip models. We made an analytical model to numerically calculate the AC transport current loss. In the model, critical current density (J/sub c/) distribution in the wire cross section is taken into consideration. It is shown by the analysis based on the model that the deviation of the measured AC loss from the Norris equations is due to inhomogeneous J/sub c/ distribution in the cross section of the tape. The J/sub c/ distribution was investigated by subdividing the YBCO layer along the longitudinal direction. The results of the investigation are compared with the J/sub c/ distribution deduced from the analysis. The loss data showed frequency dependency, which can be explained by assuming that the loss has hysteretic and eddy-current-like loss components.

Energy losses in YBCO-123 coated conductors carrying transport current in perpendicular external magnetic field

In the work we present experimental results for AC losses and critical currents of biaxially aligned YBCO-123 coated conductors, with Hastelloy as a substrate material. The critical current density of the tapes was of the order of 4.10 9 A/m 2 at the liquid nitrogen temperature. Magnetization losses, in sinusoidally varying external AC fields directed perpendicular to the plane of the tapes, were measured using a standard Lock-in technique. The frequency of the magnetic field was in a range of 7-64 Hz. The losses in YBCO are pure hysteretic for amplitudes up to 40 mT. Magnetization losses in the tape when carrying DC transport current are also reported. From obtained experimental data of dynamic resistance and the magnetization losses the total losses dissipated in the tape have been evaluated and compared with the critical state model predictions.

Dependence of AC transport current losses of HTS wires on their structures and synthesizing processes

HTS wires of various structures and synthesizing processes are being developed for power apparatus applications in the Super-GM project. AC transport current losses of four of those wires were measured by an electric method using a lock-in amplifier. Measured wires are a Bi2212 rod fabricated by the laser pedestal growth method, a Y123 tape fabricated by the pulsed laser deposition and multilayered Bi2223/Ag sheathed wires of square and tape shapes. In this paper, based on measured data, dependence of AC transport current losses of HTS wires on their structures and synthesizing processes is discussed.

AC transport current losses in HTS tapes in an assembled conductor

We developed an electric method to measure AC transport current losses in HTS tapes placed parallel on a flat plane to study on influence of magnetic field produced by the neighboring tapes on AC loss characteristics of a tape in an assembled conductor. To measure the AC losses in a tape in such arrangement electrically, proper cares for potential leads arrangements are necessary to avoid spurious loss components mixed in the measured data. In our method a combination of spiral and rectangular loops was used. Configuration of the loop arrangements was determined by a study of energy flows among the tapes. The validity of the method was verified by a calorimetric measurement conducted with the same arrangement of the tapes. The experimental data showed that the AC losses in the tape were significantly affected by the magnetic fields produced by the neighboring tapes.

AC loss characteristics of an assembled conductor of round Bi2223 Ag sheathed wires

Round-shaped Bi2223/Ag sheathed wires were developed to apply to AC superconducting apparatuses. Round high temperature superconductor wires are convenient to assemble into a twisted cable conductor to obtain homogeneous current distribution in the wires. We measured AC transport current losses in a round wire itself and a (6+1) assembled cable conductor. The experimental results showed that the AC transport current loss per one wire in the assembled conductor was larger than that in an isolated wire. Reason for this difference of the AC losses is discussed.

Power losses in multifilamentary Ag/BSCCO-2223 tape caused by AC external magnetic field and transport current

We present experimental results of self-field energy losses in multifilamentary Ag/Bi-2223 tape, carrying an AC transport current, in presence of an external DC magnetic field. The magnetic field was oriented perpendicular to the transport current flow direction and parallel to the plane of the tape. Magnetisation losses due to transverse external AC magnetic field applied to the tape when carrying DC or AC transport current, are also reported. The measurements were carried out at 77 K and at frequency of 81 Hz. The experimental results obtained are qualitatively compared to the theoretical predictions of the critical state model.