Processing and characterisation of long-length silver/bismuth-2223 tape for electric power applications
The potential of high temperature superconductivity (HTS) to raise efficiencies in electric power utilisation is dependent on the availability of HTS materials in a form which can be engineered into devices. This paper reviews a program of continuous process and product improvement which has enabled tape with lengths up to 1000 m and appropriate engineering properties to be reproducibly processed using the powder-in-tube technique. Underpinning this development of a large scale process capability, tape development on a small scale was necessary in the areas of innovative tape design, metal forming optimisation and heat treatment. In addition, techniques for the characterisation of long lengths of tape were developed. These techniques included the modelling of the effect of the self-field generated by the tape under test at 77 K to enable zero field Ic data to be determined.
Experimental study on AC losses in Ag sheathed PbBi2223 tapes with twist filaments
Abstract Experimental measurements of AC losses were carried out on Ag sheathed PbBi2223 tapes with twisted and untwisted filaments. Losses were measured at 77 K as function of frequency and magnetic field parallel and perpendicular to the tape surface, using appropriate pick-up loops. Both the first and third harmonics of the signal were measured, in order to distinguish between the hysteresis loss and other types of loss. The effect of filaments uncoupling by twisting was clearly identified. For a tape with a twist pitch of 10 mm and Ic=40 A (∼20 kA cm−2) operating at 43 Hz, the filaments are uncoupled in fields less than 40 mT, which is greater than the full penetration field for both the filaments and the tape. Hence, a reduction in the hysteretic loss of the superconducting core is realised at power frequency between 10 and 40 mT. Results form the self-field loss measurement implies the uncoupling of twisted filaments at relative low transport current (I
Methods of introducing lead into bismuth-2223 and their effects on phase development and superconducting properties
Abstract The specific method of introducing lead significantly influences the phase development and superconducting properties of Pb-doped Bi 2 Sr 2 Ca 2 Cu 3 O x (BSCCO-2223) Ag-sheathed powder-in-tube tapes. This is demonstrated in a study of tapes made from a series of powder mixtures containing the phases Bi 1.8 Pb z Sr 2.0 Ca 1.0 Cu 2.0 O 8 (2212), Ca 2 PbO 4 , Ca 2 CuO 3 , and CuO, where the lead content of 2212, z , was varied from 0.0 to 0.4. The overall composition of each mixture was the same, (Bi 1.8 Pb 0.4 Sr 2.0 Ca 2.0 Cu 3.0 O 10 ), and the amounts of each phase were varied to compensate for changes in z . In an additional mixture made from lead-free 2212, Ca 2 CuO 3 , and CuO, all lead was added as PbO. A significantly more complete 2223 formation, sharper transition temperatures, and higher critical current densities were seen when all lead was incorporated in the 2212 phase, rather than being added as either PbO or Ca 2 PbO 4 .