Cryogenic apparatus

A cryogenic apparatus, the apparatus comprising:

• an enclosure;
• a first thermo-mechanical cooler and a second thermo-mechanical cooler which project into the enclosure, at least the second thermo-mechanical cooler being a two-stage cooler, and each cooler having a fluid inlet and a fluid outlet for each stage;
• a helium gas extraction flow duct which extends into the enclosure and which communicates with a vessel to contain liquid helium within the enclosure;
• a first heat exchanger within the helium gas extraction flow duct;
• wherein the apparatus also comprises a first duct to carry helium gas from the fluid outlet of the first thermo-mechanical cooler and through the first heat exchanger to the fluid inlet of the second stage of the second thermo-mechanical cooler, and a second duct to carry liquid helium from the fluid outlet of the second stage of the second thermo-mechanical cooler into the vessel to contain liquid helium.