A Light-Weight Rugged Conduction-Cooled NbTi Superconducting Magnet for U.S. Navy Minesweeper Applications

Abstract

A superconducting magnet using an aluminum-stabilized NbTi coil cooled by two Gifford-McMahon rare earth (GM-RE) cryocoolers has been built and successfully tested in support of the U.S. Navy’s efforts to develop the technology for shallow water magnetic mine countermeasures. The 3.4 T, 0.5 meter diameter coil is supported in a vacuum vessel with a series of re-entrant filament-wound cylinders made from E-glass, that are designed to withstand large shock and vibration loads. This high load combined with the need to minimize conduction heat leak to the coil has motivated the need for the lighter weight conductor, thus reducing the stuctural burden. The Navy’s additional requirement to minimize the overall system weight has resulted in a compact re-entrant cylinder cold-to-warm support (CTWS) structure design with integrated thermal intercepts and shielding. Structural joints at E-glass and metal transitions in the CTWS use a combination adhesively bonded and riveted scarf joint configuration. Low impedance thermal interfaces between the cryocoolers and the coil, shield, and current leads were developed to ensure that coil temperatures remain well below the NbTi critical transition temperature during operation.