Technical Reports

Novel Cryogen-free Actively Shielded Superconducting Magnets for Maglev Vehicles

  • 01
  • Jun
  • 1992
AUTHOR: M. E. Vermilyea
OFFICE: RPD
REPORT NUMBER: DOT/FRA/NMI-92/07
SUBJECT: Maglev
KEYWORDS: Shielding, Cryogenics, Magnet System
ABSTRACT: This report presents the results of a research effort into the design of a shielded superconducting magnet system for a maglev vehicle. The magnet design is based on a novel cryogen-free technology which allows operation without the use of any cryogenic fluids. This is accomplished by the use of a two- stage Gifford-McMahon (G-M) cryogenic refrigerator to provide cooling of the coil and a single cryostat thermal radiation shield by conduction. The design operating temperature of the magnet is 7.5 K, and that of the shield is 43 K. The magnet is wound with a tape form of niobium tin superconductor which allows operation at a module current density of 8100 A/cm2 at a flux density of 3.4 T at the 7.5 K temperature with a margin of 4.5 K to critical temperature. The resulting magnet design is more reliable, rugged, and less expensive and heavy than a comparable pool cooled system, and is recommended for application to any maglev vehicles developed in the United States requiring superconducting magnets. Shielding of the passenger compartment of the vehicle from the DC magnetic field of the superconducting magnets is also investigated here for an assumed geometry. The geometry used is that of a sidewall, null-flux levitation and propulsion system, with the planes of the vehicle coils in a vertical orientation. Both active and passive shielding techniques are reviewed and applied to the assumed coil and vehicle geometry, with variations on the geometry considered to determine their effect on reducing the field in the passenger compartment Options for reducing the field to certain levels are presented. The basic conclusion of the shielding study is that shielding using active coils is rather ineffective for the assumed geometry, and that the only realistic shielding methods are passive shielding (using iron in the vehicle structure) and shielding by distance (raising the vehicle farther above the magnets).
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