A persistent-mode 0.5 T solid-nitrogen-cooled MgB 2 magnet for MRI

Abstract This paper presents construction details and test results of a persistent-mode 0.5 T MgB 2 magnet developed at the Francis Bitter Magnet Laboratory, MIT. The magnet, of 276 mm inner diameter and 290 mm outer diameter, consisted of a stack of eight solenoidal coils with a total height of 460 mm. Each coil was wound with monofilament MgB 2 wire, equipped with a persistent-current switch and terminated with a superconducting joint, forming an individual superconducting loop. Resistive solder joints connected the eight coils in series. The magnet, after being integrated into a testing system, immersed in solid nitrogen, was operated in a temperature range of 10–13 K. A two-stage cryocooler was deployed to cool a radiation shield and the cold mass that included mainly ∼60 kg of solid nitrogen and the magnet. The solid nitrogen was capable of providing a uniform and stable cryogenic e…