Illustration of a pulse tube refrigerator.
Credit: S. Kelley/NIST
By modifying a refrigerator commonly used in both research and industry, researchers at the National Institute of Standards and Technology (NIST) have drastically reduced the time and energy required to cool materials to within a few degrees above absolute zero. The scientists say that their prototype device, which they are now working to commercialize with an industrial partner, could annually save an estimated 27 million watts of power, $30 million in global electricity consumption and enough cooling water to fill 5,000 Olympic swimming pools.
From stabilizing qubits (the basic unit of information in a quantum computer) to maintaining the superconducting properties of materials and keeping NASA’s James Webb Space Telescope cool enough to observe the heavens, ultracold refrigeration is essential to the operation of many devices and sensors. For decades, the pulse tube refrigerator (PTR) has been the workhorse device for achieving temperatures as cold as the vacuum of outer space.
These refrigerators cyclically compress (heat) and expand (cool) high pressure helium gas to achieve the “Big Chill,” broadly analogous to the way a household refrigerator uses the transformation of freon from liquid to vapor to remove heat. For more than 40 years, the PTR has proven its reliability, but it is also power-hungry, consuming more electricity than any other component of an ultralow temperature experiment.
Animations show a simplified version of a pulse tube refrigerator (PTR), commonly used to cool materials to a few degrees above absolute zero by compressing and expanding helium gas held under high pressure. NIST researchers optimized the efficiency of the PTR, dramatically reducing the amount of time and energy required to reach ultracold temperatures, by continuously adjusting the valve connecting the pulse tube to a reservoir of helium gas.
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