Lambda point refrigerator

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A lambda point refrigerator is a device used to cool liquid helium, typically around a superconducting magnet, from approximately 4.2 K to temperatures near the lambda point (approximately 2.17K), just above normal fluid helium (helium I)'s transition to the superfluid helium II. The lowering of the temperature is achieved by reducing the pressure of the helium via the use of a pump. While liquid helium typically has poor thermal conductivity, convective currents setup within the helium bath provide a constant flow of this low-pressure helium, allowing temperatures below 4.2K to be realized in the helium bath.