Abstract: Cooling apparatus comprises a cooling system defining a closed path around which a coolant flows. The system includes a pump for causing coolant flow, a supply line extending from the pump to a cold location, positioned in a cryostat, in order to cool that location, and a return line extending from the cold location to the pump. The pump is located externally of the cryostat. A first heat exchanger is positioned within the cryostat and links the supply and return lines to allow heat exchange therebetween such that coolant flowing in the supply line is cooled by coolant flowing in the return line. A refrigerator is provided having a cooling stage within the cryostat and coupled to the supply line downstream of the first heat exchanger such that coolant reaching the first cooling stage has been precooled by the first heat exchanger.