1-K pot

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A 1-K pot (i.e. 1-

device used to attain temperatures down to approximately 1 kelvin.

The 1-K pot is a small vessel in a cryogenic system that is filled with

.

At atmospheric pressure, ⁴He (the more abundant isotope of helium) liquefies at 4.2 K. By employing evaporative cooling, temperatures down to 1 K can be easily produced. While this technique is fairly simple to operate, it is inefficient for large helium baths because about 50% of the liquid helium must evaporate to attain to the lowest temperatures. If only a small volume needs to be cooled to 1 K, the 1-K pot is used. Only the surface of the small 1-K pot is pumped, leaving the rest of the liquid helium bath at atmospheric pressure.

While this method is commonly used in simple cryogenic systems to cool objects down to 1 K, it is also fairly popular in more complicated cryogenic systems to bootstrap to lower temperatures. For example, in a ³He refrigerator, condensed ³He (a rare isotope of helium) is evaporatively cooled and can attain temperatures as low as 200 mK. But the ³He must be condensed to a liquid first, and a 1-K pot is typically used for this purpose.

Another example is a dilution refrigerator, where a mixture of ³He and ⁴He forms a phase boundary in a mixing chamber and can cool down to a few millikelvins. Dilution refrigerators typically use a 1-K pot to condense the ³He/⁴He mixture.

References

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