Development and Testing of a BI-2212 Textured Powder Conductor

Abstract

Superconducting wires based on the high field superconductor Bi_(2)Sr_(2)Ca_(1)Cu_(2)O_(8)+x are an enabling technology for the development of very high field (>18 T) magnets. While these conductors have the potential to serve as the conductors for magnets operating in excess of 45 T, the achieved current carrying capacity of these materials is too low for economical implementation in high field operation. This is in part due to low density of the superconductors within the cores, the presence of current occluding non-superconducting phases, and a non-optimum alignment of the superconducting particles that form the conductor. The body of work reported in this dissertation aims to develop methods to align (texture) the superconducting particles within the conductors, to enhance the density of the superconducting filaments, to examine a heat treatment that does not form parasitic phases, and to demonstrate that long lengths of superconducting wire can be fabricated with these properties.

Three general experimental thrusts are carried out within the work. First, methods for texturing Bi-2212 loose powders were developed and the products of these developments were characterized via x-ray diffraction and microscopy to qualify the degree of imparted texture. The second thrust focused on the development of a monocore wire based on a high density textured Bi-2212 precursor. Multiple wires were extruded and drawn through traditional processes and the products were characterized microscopically to ascertain the quality of the products. The third and final thrust was the development of a non-melt heat treatment that was shown to grow grains of Bi-2212 powder and densify composites. Measurements of the transport critical currents for the heat treated conductors were carried out in boiling liquid helium and background magnetic fields of up to 5 T. These results were correlated to microstructural observations. Ultimately, it was found that the connections between grains in the sintered conductors were insufficient to allow robust transport current and only 1% of the predicted transport currents were reached through the sintering study.