Enhanced Quench Propagation in hbox Bi 2 hbox Sr 2 hbox CaCu 2 hbox O x and hbox YBa 2 hbox Cu 3 hbox O 7 - x Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator

• Published in: IEEE transactions on applied superconductivity Vol. 23; no. 5; p. 7201311
• Main Authors: Ishmael, Sasha, Luo, Haojun, White, Marvis, Hunte, Frank, Liu, X T, Mandzy, Natalia, Muth, John F, Naderi, Golsa, Ye, Liyang, Hunt, Andrew T, Schwartz, Justin
• Format: Journal Article
• Language: English
• Published: 01.10.2013
• Subjects: Coils; DOPING; Insulation; INSULATION (ELECTRICAL); INSULATORS; MAGNETS; MICROSTRUCTURES; Mullite; Nanostructure; Normal zone propagation; QUENCHING MECHANISMS; SUPERCONDUCTORS; Thermal conductivity; YBCO superconductors; YTTRIUM OXIDE
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2013.2269535

The significant amount of energy stored in a large high-field superconducting magnet can be sufficient to destroy the coil in the event of an unprotected quench. For magnets based on high-temperature superconductors (HTSs), such as hbox Bi 2 hbox Sr 2 hbox CaCu 2 hbox O x (Bi2212) and hbox YBa 2 hbox Cu 3 hbox O 7 - x (YBCO), quench protection is particularly challenging due to slow normal zone propagation. A previous computational study showed that the quench behavior of HTS magnets is significantly improved if the turn-to-turn electrical insulation is thermally conducting, enhancing 3-D normal zone propagation. Here, a new doped-titania electrical insulation with high thermal conductivity is evaluated. The thermal conductivity of the insulation is measured at cryogenic temperatures, and its chemical compatibility with Bi2212 round wires is determined. Thin layers of the insulation are deposited onto the surface of Bi2212 and YBCO wires, which are then wound into small coils to study the quench behavior. Results show that the critical current and homogeneity of Bi2212 coils are improved relative to coils reacted with mullite insulation. Relative to similar coils with conventional insulation (mullite for Bi2212 and Kapton for YBCO), the turn-to-turn quench propagation is increased by a factor of 2.8 in Bi2212 coils at 4.2 K and self-field and by a factor of 2.5 in YBCO coils at 4.2 K and 5 T. These results indicate that doped-titania insulation may significantly improve Bi2212 and YBCO coils. Increased normal zone propagation velocity enhances quench detection and quench protection, and the thinness of the insulation relative to the most common alternatives increases the magnet winding pack current density and reduces the coil specific heat.