M. Ciszek

The effect of potential contact position on AC loss measurements in superconducting BSCCO tape

Abstract AC losses in (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x silver-sheathed tape were measured as a function of frequency and amplitude of a sinusoidall y varying transport current. Experimental results show that energy losses are purely hysteretic in nature in the range of applied frequencies for transport currents below the critical value I c . The lossy component of the measured voltage is very dependent on the position of the potential taps placed onto the surface of the tape. This can be explained using the theory of Norris [J. Phys. D 3 (1970) 489] for ellipsoidal conductors. It means that neither voltage gives an accurate measurement of the loss. The error is least for the side contacts but still varies from 40% at I c to a factor of four at 0.1 I c .

Influence of external magnetic field and its orientation on transport AC losses in Bi-2223 and Tl-1223 silver sheathed tapes

In the paper we report measurements of energy losses caused by an AC transport current in silver sheathed multifilamentary Bi-2223 and mono core Tl-1223 tapes, as a function of the magnitude and orientation of the applied external magnetic field. The external magnetic field was rotated in the range of 0 to /spl plusmn/90 degrees with respect to the plane of the tapes, and was In all cases perpendicular to the transport current flow. The transport current losses in a range of DC applied fields are consistent with the Norris equation provided the DC critical current at the same applied field is used in his expression for the loss.

AC losses of Ag-(Bi,Pb)SrCaCuO-2223 tapes in combination of transverse external magnetic field and transport current

The authors present the results of measurements of the AC transport (self-field) and magnetic losses on silver sheathed (Bi,Pb)SrCaCuO-2223 tapes prepared by the powder in tube method. In the frequency range 30-540 Hz the transport current losses are hysteretic in nature. Losses arising from AC external magnetic field (frequency range 65-207 Hz, amplitude up to 60 mT) are compared with losses generated by AC transport currents. The measured transport loss voltage depends strongly on the position of the potential taps on the surface of the tapes. Losses due to combined AC applied magnetic fields and transport currents are also reported.<<ETX>>

Energy dissipation in high temperature ceramic superconductors

Abstract Losses in high- T c superconductors are of vital importance in practical applications. The mechanisms are similar to those in low- T c materials but there are a number of complications. In this paper the loss mechanisms in different regimes are summarized and simple approximate expressions obtained. Losses due to the transport current are analysed with the theory of Norris for elliptical conductors. This predicts different loss voltages according to where the voltage contacts are placed on the conductor which has been confirmed experimentally. This poses difficulties in turning experimental data into reliable loss measurements, but a series of experiments with different contact layouts and phase setting techniques is found to give consistent results, in good agreement with theory.

AC LOSSES AND CRITICAL CURRENTS IN AG/(TL,PB,BI)-1223 TAPE

Abstract The results of AC loss measurements of silver-sheathed (Tl,Pb,Bi)-1223 tapes prepared by the powder-in-tube method are presented. Losses arising from an external AC magnetic field are compared with those generated by AC transport currents (self-field losses). Experimental results, obtained by both methods, show that energy losses are purely hysteretic in nature in the range of applied frequencies (30–200 Hz). Critical current densities are derived from the magnetic-loss data and compared with those measured by the four-point transport method. Further, the dependence of the transport critical currents on the external DC magnetic field, for different geometrical configurations of the tapes with respect to the field, i.e. field parallel or perpendicular to the plane of the sample, are presented. The experimental results are compared with theoretical predictions based on the critical-state model.

Transport AC losses in multifilamentary Ag/Bi-2223 tapes in low external DC magnetic fields

Abstract Experimental results of measurements of the AC transport current losses on silver sheathed (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x multifilamentary tapes are presented. In the frequency range 33–180 Hz the self-field losses are hysteretic. Transport loss changes due to low DC, applied transverse magnetic fields are also studied. External transverse DC magnetic field causes an increase in the transport losses due to lowering of the critical current I c of the superconductor. Critical current dependence on the external magnetic field extracted from loss data is compared with that measured directly by standard DC four-probe measurements.

Thallium cuprate 1223 type.: I. Its elaboration and dependence of chemical and thermal stability and of superconducting transition temperature on Tl/Pb and Sr/Ba substitutions

Abstract The formation of samples with nominal composition (Tl x Pb 1− x )(Sr 1− y Ba y ) 2 Ca 2 Cu 3 O z was followed by X-ray diffraction study. With the chosen elaboration conditions, the 1223 phases were formed in two steps with a 1212 type phase observed as an intermediate compound. From the results, the limits of the 1223 single phase field were determined for temperature below 930°C and under 1 bar of oxygen. Samples with 91% purity were obtained and for compositions located outside the limits of the monophased field, a Tl/Pb–Sr/Ba-1212 and a substituted Tl/Pb and Sr/Ba perovskite were found as the main impurities.

Enhancement of Microstructural and Magnetic Properties by Li-doping in Tl,Pb-1223 Superconductors

Polycrystalline Tl0.5Pb0.5Sr2Ca2Cu3LiyOx samples were synthesized. After processing under the same conditions, the Li-doped samples (y = 0.2) showed an average grain size three times larger than that of a typical undoped Tl,Pb-1223 sample (y = 0), and a 30% increase in sample density. The irreversibility line has significantly shifted to higher field with Birr ( 77K) ≅ 12 tesla. The intragranular critical current densities, estimated through the Bean model, are higher in Li-doped samples in temperatures below 77K and external magnetic fields greater than 2 tesla. The Tc,onset, of the Li-doped samples are lowered by typically 2-5 K compared with the undoped samples.

CRITICAL CURRENT ANISOTROPY OF TL-1223 SUPERCONDUCTORS

A comparative study of the critical current anisotropy of Tl-1223 conductors manufactured by different techniques, prepared from different compositions and originating from different research laboratories is presented and discussed. For highly oriented layers, with the magnetic field (B) parallel to the ab plane, the normalised critical current density (j) versus magnetic field characteristic shows very little drop of j value due to the intrinsic properties of the Tl-1223 phase, while all powder-in-tube conductors show a rapid drop of j value in fields as low as 10 mT. For all powder-in-tube conductors the anisotropy coefficient k shows a very pronounced minima at fields up to 30 mT followed by a monotonic decrease of anisotropy with increase of the magnetic field. This is due to poor grain alignment and a demagnetising effect in the powder-in-tube Tl-1223 tapes.

Anomalies in ac susceptibility and weak ferromagnetic behavior of Gd2CuO4

Abstract We have made ac susceptibility (acs) and dc magnetisation (dcm) measurements of Gd2CuO4. Anomalous behavior of acs in the temperature range between TNGd≈7 K and TL≈20 K is reported. At temperatures between TL and TNCu≈280 K, in-phase and out-of-phase parts of acs are strongly dependent on both the amplitude and frequency of excitation field, passing through maximum at about 200 K. In this range, magnetic field dependences of dcm show distinct hysteresis loops with coercive field equals to about 20 Oe.