Design, Fabrication, and Testing of the Aliss Superconducting Mine-Countermeasures Magnet

Abstract

A conduction-cooled lightweight 7.5 MJ superconducting (SC) magnet capable of sustaining 100 g shock loads has been built and has undergone initial testing in support of the U.S. Navy’s mine warfare program¹. The solenoid magnet coil uses Cu:NbTi (4:1) superconductor wire and operates at a steady state temperature of less than 5 K while being cooled by two Gifford McMahon rare earth cryocoolers. The cryocoolers are detachable via a cold sleeve. Oxygen and ethane heat pipes thermally link the coil to the cryocooler’s first stages to reduce cooldown time. The coil’s cold-to-warm support structure comprises a series of re-entrant cylinders made of fiberglass reinforced epoxy composite. The vacuum vessel and thermal shields are constructed from formed aluminum isogrid panels which maximize the strength-to-weight ratio. The magnet uses grain-aligned YBCO high-Tc current leads operating between 30 K and 4 K, and the maximum design current is 147 Amps. The magnet has demonstrated stable operation up to 6.7 K at 60% of rated current. Operation of the magnet and its ancillary systems along with monitoring of all critical performance parameters is accomplished via a laptop computer. Additional tests are planned during which the magnet and its control system will be readied for participation in a joint Army-Navy Advanced Technology Demonstrator program involving mine sweeping exercises in 1998. During these exercises, the SC magnet system will be mounted on a small Naval craft designed to demonstrate new shallow water mine countermeasures technologies at sea.