A “permanent” high-temperature superconducting magnet operated in thermal communication with a mass of solid nitrogen

• Published in: Cryogenics (Guildford) Vol. 42; no. 3; pp. 229 - 244
• Main Authors: Haid, Benjamin J, Lee, Haigun, Iwasa, Yukikazu, Oh, Sang-Soo, Kwon, Young-Kil, Ryu, Kang-Sik
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-03-2002; Elsevier
• Subjects: Applied sciences; Computer simulation; Critical current density (superconductivity); Cryogenics; Electric power systems; Energy; Energy. Thermal use of fuels; Exact sciences and technology; High temperature superconductors; HTS magnet; Magnetic field effects; Nitrogen; Permanent magnets; Persistent-mode; Refrigerating engineering. Cryogenics. Food conservation; Solid nitrogen; Superconducting tapes; Vacuum pumps; Persistent-mode; Solid nitrogen; HTS magnet; Superconducting magnet; Solid state; Cooling; Cryogenics; Superconducting generators; Nitrogen; High temperature superconductor
• ISSN: 0011-2275; 1879-2235
• DOI: 10.1016/S0011-2275(02)00022-X

A new design for a portable “permanent” superconducting magnet system is explored. The design involves a persistent-mode high-temperature superconducting (HTS) magnet that is cooled by a solid heat capacitor. The system is an alternative to permanent low-temperature superconducting (LTS) magnet systems where the magnet is cooled by a bath of liquid helium.
An apparatus was constructed to demonstrate stable operation of a permanent magnet wound with Bi2223/Ag conductor while in thermal communication with a mass of solid nitrogen. The apparatus includes a room-temperature bore and can function while it stands alone, detached from its cooling source, power supply, and vacuum pump. The magnet is operated in the 20–40 K temperature range. This apparatus is the first to demonstrate the operation of a superconducting magnet with a permissible temperature variation exceeding a few degrees kelvin. Models are developed to predict the experimental system's warming trend and magnetic field decay. The models are validated with a good agreement between simulations based on these models and experimental results. The results indicate that present HTS conductor critical current and index are not yet sufficient to provide field strengths and field decay time constants that are required for typical persistent-mode applications.