By modifying a refrigerator commonly utilized in each research and industry, researchers on the National Institute of Standards and Technology (NIST) have drastically reduced the time and energy required to chill materials to inside just a few degrees above absolute zero. The scientists say that their prototype device, which they are actually 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 essential unit of knowledge in a quantum computer) to maintaining the superconducting properties of materials and keeping NASA’s James Webb Space Telescope cool enough to look at the heavens, ultracold refrigeration is important to the operation of many devices and sensors. For a long time, the heartbeat tube refrigerator (PTR) has been the workhorse device for achieving temperatures as cold because the vacuum of outer space.
These fridges cyclically compress (heat) and expand (cool) high pressure helium gas to realize the “Big Chill,” broadly analogous to the best way a household refrigerator uses the transformation of freon from liquid to vapor to remove heat. For greater than 40 years, the PTR has proven its reliability, but it is usually power-hungry, consuming more electricity than some other component of an ultralow temperature experiment.
When NIST researcher Ryan Snodgrass and his colleagues took a more in-depth take a look at the refrigerator, they found that manufacturers had built the device to be energy efficient only at its final operating temperature of 4 kelvin (K), or 4 degrees above absolute zero. The team found that these fridges are extremely inefficient at higher temperatures — an enormous issue since the cooldown process begins at room temperature.
During a series of experiments, Snodgrass, together with NIST scientists Joel Ullom, Vincent Kotsubo and Scott Backhaus, discovered that at room temperature, the helium gas was under such high pressure that a few of it was shunted through a relief valve as an alternative of getting used for cooling. By changing the mechanical connections between the compressor and the refrigerator, the team ensured that not one of the helium could be wasted, greatly improving the efficiency of the refrigerator.
Specifically, the researchers continually adjusted a series of valves that control the quantity of helium gas flowing from the compressor to the refrigerator. The scientists found that in the event that they allowed the valves to have a bigger opening at room temperature after which progressively closed them as cooling proceeded, they may reduce the cooldown time to between one half and one quarter of what it’s now. Currently, scientists must wait a day or more for brand new quantum circuits to be cold enough to check. Because the progress of scientific research could be limited by the point it takes to achieve cryogenic temperatures, the faster cooldown provided by this technology could broadly impact many fields, including quantum computing and other areas of quantum research. The technology developed by the NIST team could also allow scientists to exchange large pulse tube fridges with much smaller ones, which require less supporting infrastructure, Snodgrass said.
The necessity for these fridges will greatly expand as research on quantum computing, together with its reliance on cryogenic technology, continues to grow. The modified PTR would then save a much greater sum of money, electricity and cooling water. Along with supporting a burgeoning quantum economy, the device would also expedite research because scientists would not must wait days or even weeks for qubits and other quantum components to chill.
