Cryogenic magnet systems

Claim 1

A cryogenic superconducting magnet system for use in magnetic resonance imaging (MRI) devices, said system comprising: an evacuated container, a first tank mounted within said evacuated container and thermally insulated therefrom, boiling liquid helium disposed in said first tank and exhausted to the outside of said container, a cryogenic superconducting magnet disposed in said first tank, a metallic heat radiation shield disposed in said evacuated container and substantially surrounding said first tank, said shield being thermally insulated from both said container and said first tank, and a neon refrigeration system external to said shield for cooling said shield, said neon refrigeration system including neon refrigerant, a second tank for containing said neon refrigerant in its liquid state, at least one thermal siphon for circulating said neon refrigerant by convection from said second tank to said shield, the boiling of said neon refrigerant at said shield acting to circulate said neon refrigerant in said thermal siphon and cool said shield, a mechanical cryocooler remote from said container for condensing said neon refrigerant from the gaseous to the liquid state, and thermally insulated transfer means for transferring said neon refrigerant in its gaseous state from said second tank to said cryocooler and said neon refrigerant in its liquid state from said cryocooler to said second tank.