Lambda point refrigerator

A lambda point refrigerator is a device used to cool liquid helium, typically around a superconducting magnet or for low temperature measurements, from approximately 4.2 K to temperatures near the lambda point of helium (approximately 2.17 K), the temperature at which normal fluid helium (helium I) transitions to the superfluid helium II. Cooling is achieved by pumping the liquid helium in the bath through a cooling coil via a needle valve and vacuum pump. The reduced pressure in the coil causes some of the helium to evaporate, creating a two-phase system within the cooling coil.

Source: Wikipedia — Lambda point refrigerator (CC BY-SA 4.0)