High-field Second Generation Cable with Sub-millimeter Filaments

Second-generation high temperature superconductors (2G-HTS) enable ultra-high field magnets for research and industrial applications. However, 2G-HTS wires are currently manufactured as ~ 10 mm wide tapes. Such wide tape is mechanically difficult to wind and because of its width, the tape incurs high hysteresis losses and suffers poor quench stability. Brookhaven Technology Group, Inc. (BTG) proposes to use its recently developed exfoliation process to build and characterize a multiconductor HTS cable using transposed ultra-narrow, sub-mm filaments. The new cable architecture is expected to reduce the hysteresis losses of high-field dipole magnets by a factor of 20, improve flexibility of the wire, and increase quench stability. BTG’s newly developed exfoliation process will be used as a first step in the manufacture of the ultra-thin, light weight filaments. In the exfoliation process, YBCO superconductor is separated from the substrate, which eliminates the danger of later delamination and it reduces the weight and material costs among other advantages. This step will be followed by a slicing operation in which an infra-red fiber laser will be used to slice the exfoliated YBCO tape into sub-millimeter filaments. Phase I activities will include the following tasks: (i) laser slice one meter lengths of exfoliated filaments into 1000 m, 500 m and 200 m widths using a dedicated short focal length laser head. (ii) bundle the three filament widths into twisted cables using a specially developed twisting/bundling machine. (iii) perform low-temperature transport measurements of the stack properties; quantify the degree of current sharing between filaments and characterize the mechanical and electrical performance of the cables. In the end of Phase I BTG will demonstrate a 1 m long, coupon of superconducting cable comprised of at least 10 sub-mm filaments. This technology is expected to produce a cable with magnetization loss approaching that of a Nb-Ti cable. The Phase II goal will be to design and build a high-speed fiber laser slicing facility that can manufacture ~ 1 km lengths of filamentized, fully transposed, multiconductor HTS cable. The hysteresis loss is a major obstacle for application of 2G superconductor not only in high-field magnets, but also in power transmission and power management. Superconducting power cables can deliver large amounts of power in a very small cross-section. However, most of the power applications involve 60 Hz alternating current, which generates high losses in the superconductor. This technology is directly applicable to loss reduction in transmission cables and fault current limiters.