No abstract

HTS coated conductors (CC's) with substrates of magnetic materials such as Ni-alloys are expected to be promising for practical applications because Ni-alloys are well-texturized by simple processes and production costs of the conductors are significantly reduced. In the former works, it was shown by experiments that HoBaCuO-123 CC's with Ni-alloy substrates exhibit higher AC transport current losses than CC's with non-magnetic Hastelloy substrates. In this work, the AC transport current loss characteristics of stacked conductors composed of a pair of HoBCO CC's with Ni-alloy substrates are experimentally investigated to study a method to suppress the AC transport current losses. It is found that AC transport current losses can be reduced in the stack arrangement by the minimization of influence of the magnetism of the substrates canceling self-fields in the substrates.

Ferromagnetic material was electroplated onto the surface of the Bi2223/Ag multi-filamentary tape and as a result changed the Ic(B) characteristic of the tape correspondingly. A numerical simulation was used to investigate the influence of ferromagnetic shielding (FS) on the performance of the tape, in particular the Ic behaviour under perpendicular external fields. Using finite element analysis, we are able to understand how FS alters the flux distribution within the superconductor region under any arbitrary shielding structure. The shielding width, thickness and nonlinear property of the ferromagnetic material were taken into account for the simulation. Finally, optimized shielding parameters in association with different operating fields were suggested and these values could be considered for the next run of experimental work.

Reduction of dissipation at the transport of alternating current as well as when exposed to a time varying magnetic field has been observed in the tape from high-temperature superconductor Bi2Sr2Ca2Cu3O10 covered by a Ni sheath at the edges. The improvement of critical current can explain this achievement only in part. Analysis of experimental data shows that also a more favorable pattern of the magnetic flux penetration should take place.

Improvement of critical current and reduction of AC loss is presented for a common multifilamentary Bi-2223/Ag tape with thin nickel layer electroplated at the edges. Numerical calculations using a commercial finite-element code have been carried out to find the distributions of electrical current and magnetic field when the whole section is filled with the critical current density. The dependence of critical current density on local magnetic field and its orientation was taken into consideration, allowing to understand the mechanism of increase. Optimization of the cover thickness and width would be possible due to these calculations. AC loss was investigated experimentally in the condition of AC transport and simultaneous action of AC magnetic field in phase with transport current. Reduction of both the transport loss and the magnetization loss has been observed, as well as the loss at simultaneous action of transport AC and applied AC field.Index Terms-AC losses, critical current, high temperature superconductors, soft ferromagnetic cover.