Development of Low-J _c Applications of High-T _c Superconductors Based on Extended Thick Films Sprayed on Metallic Substrates with the HVOF Technique

Abstract

Several low critical-current applications of high-T _c superconductors (HTS) are possible, some of which already have industrial potential. Three of them are being explored which make use of YBCO or BiSCCO extended thick (> 50 μm) films sprayed on metallic substrates by means of the HVOF thermal spray technique. The more extensively studied, so far, is magnetic shielding for cancellation of the magnetic field inside enclosures. With a single layer, attenuation factors of the external magnetic field greater than 10⁴ are obtained for static magnetic fields, much better than using multiple layers of conventional highpermeability materials. The maximum shielded field of ≈ 1 · 10⁻⁴ T can easily be improved to ≈ 0.1 T by using a secondary shield made of low-cost ferromagnetic materials. A second application, under development, is thermal shielding, taking advantage of the fact that below T _c a superconducting surface reflects most of the thermal radiation. Heat transfer can be reduced to levels comparable with those obtained with the best multilayer insulation techniques. A third application is for magnet current leads, with currents < ≈ 100 A. In this case, the powder-in-tube technique or the use of bulk materials is exceedingly costly and the current density provided by these techniques needlessly high. The use of low-conductivity metal strips coated with superconducting thick films allows one to better compromise performances and costs. A review of the state-of-the-art is provided and some of the latest results are reported.