SUPERCONDUCTING MAGNET WITH COLD HEAD THERMAL PATH COOLED BY HEAT EXCHANGER

A superconducting magnet includes a liquid helium reservoir (14), superconducting magnet windings (12) disposed in the liquid helium reservoir, and a vacuum jacket (20) surrounding the liquid helium reservoir. A cold head (30) passes through the vacuum jacket. The cold head has a warm end (32) welded to an outer wall (22) of the vacuum jacket and a cold station (46) disposed in the liquid helium reservoir. A heat exchanger (60) is disposed inside the vacuum jacket and secured to or integral with the cold head. The heat exchanger includes a fluid passage (62) having an inlet (64) in fluid communication with the liquid helium reservoir and having an outlet (66) in fluid communication with ambient air. While the cold head is turned off, gas helium flows from the liquid helium reservoir to ambient air via the heat exchanger, thereby cooling the non-operating cold head.