Research from North Carolina State University shows that a type of modified titania, or titanium dioxide, holds promise as an electrical insulator for superconducting magnets, allowing heat to dissipate while preserving the electrical paths along which current flows. Superconducting magnets are being investigated for use in next-generation power generating technologies and medical devices.
Regular conductors conduct electricity, but a small fraction of that energy is lost during transmission. Superconductors can handle much higher currents per square centimeter and lose virtually no energy through transmission. However, superconductors only have these desirable properties at low temperatures.
“Superconducting magnets need electrical insulators to ensure proper operation,” says Dr. Sasha Ishmael, a postdoctoral researcher at NC State and lead author of a paper describing the work. “Changing the current inside the superconductor is important for many applications, but this change generates heat internally. The magnets will operate much more safely if the electrical insulators are able to shed any excess heat. Otherwise, the higher temperatures could destroy the superconductor.
“This titania-based material is up to 20 times better at conducting heat than comparable electrical insulators,” Ishmael says. “It has characteristics that are very promising for use as electrical insulators for superconducting technologies.”
The precise chemical composition of the modified titania is proprietary information. The material’s development and characterization was a joint effort between NC State and nGimat LLC, based in Lexington, Kentucky.
“We’re now looking at the effect of radiation on this material, to determine if it can be used for high energy physics applications, such as particle colliders,” says Dr. Justin Schwartz, senior author of the paper and Kobe Steel Distinguished Professor and head of the Department of Materials Science and Engineering at NC State.
The paper, “Thermal conductivity and dielectric properties of a TiO2-based electrical insulator for use with high temperature superconductor-based magnets,” is published online in the journal Superconductor Science and Technology. The paper was co-authored by M. Slomski, H. Luo, J.F. Muth, T. Paskova, and W. Straka of NC State, and M. White, A. Hunt, N. Mandzy, and R. Nesbit of nGimat LLC.
The research was supported by the Department of Energy under grant DE-SC0004657-001 and the National Science Foundation under grant CBET-1336464.
Note to Editors: The study abstract follows.
“Thermal conductivity and dielectric properties of a TiO2-based electrical insulator for use with high temperature superconductor-based magnets”
Authors: S.A. Ishmael, M. Slomski, H. Luo, J.F. Muth, T. Paskova, W. Straka, and J. Schwartz, North Carolina State University; M. White, A. Hunt, N. Mandzy, and R. Nesbit, nGimat LLC.
Published: Aug. 20 in Superconductor Science and Technology
Abstract: Quench protection is a remaining challenge impeding the implementation of high temperature superconductor (HTS)-based magnet applications. This is due primarily to the slow normal zone propagation velocity (NZPV) observed in Bi2Sr2CaCu2OX (Bi2212) and (RE)Ba2Cu3O7-x (REBCO) systems. Recent computational and experimental findings reveal significant improvements in turn-to-turn NZPV, resulting in a magnet that is more stable and easier to protect through three-dimensional normal zone growth [1, 2]. These improvements are achieved by replacing conventional insulation materials, such as Kapton and mullite braid, with a thin, thermally conducting, electrically-insulating ceramic oxide coating. This paper reports on the temperature-dependent thermal properties, electrical breakdown limits and microstructural characteristics of a titanium oxide (TiO2) insulation and a doped-TiO2-based proprietary insulation (doped-TiO2) shown previously to enhance quench behavior . Breakdown voltages at 77 K ranging from ~1.5 kV to over 5 kV are reported. At 4.2 K, the TiO2 increases the thermal conductivity of polyimide by about a factor of 10. With the addition of a dopant, thermal conductivity is increased by an additional 13%, and a high temperature heat treatment increases it by nearly an additional 100%. Similar increases are observed at 77 K and room temperature. These results are understood in the context of the various microstructures observed.