A vertically reciprocating NbTi solenoid used in a regenerative magnetic refrigerator

An 8.2T-NbTi superconducting solenoid used for periodic magnetization by vertical motion along a bed of magnetocaloric material in a regenerative magnetic refrigerator using all active magnetic regenerator (AMR) has been designed, fabricated, and tested. The magnet design had two primary requirements: field uniformity and minimum stray flux. The magnet is charged with demountable leads and switched into persistent mode. Wheels and tracks guide the magnet in a liquid-helium dewar which is part of a larger environment cooled by a gas cycle refrigerator. Positioning of the magnet is determined by a computer-driven, PI-controlled linear actuator servo. design, test configuration, and test results of the solenoid systems are described.