Picture an apothecary scale that can weigh a speck of dust on your palm. Such a scale for electricity is called a cryogenic current comparator. Previously, it had to be kept in a bath of liquid helium, like a fish in an aquarium. Now Japanese engineers have done it differently: they slipped a gas jacket over the instrument.
In the chamber, gaseous helium transfers cold from the refrigerator walls to the instrument. The pressure is chosen so that the gas does not interfere with measurements. It turns out that at a pressure of about 20 pascals, the accuracy is as good as with liquid helium. An uncertainty of one part per billion is achieved in just one hundred seconds.
Previously, one cooling cycle consumed liters of liquid helium. Now less than a liter of gas suffices, which is equivalent to about one milliliter of liquid. Helium is becoming more expensive on Earth, so this saving matters. The instrument has been operating since September 2025 and helps calibrate standard resistors.
Gaseous helium at 4.2 K remains a gas at pressures below 100 kPa, so it can be used as a heat-exchange medium without the risk of condensation. A consumption of less than 1 liter of gas per cycle is equivalent to just 1 milliliter of liquid helium, which is hundreds of times less than traditional cryostats.
In Arkady and Boris Strugatsky's novel 'Monday Starts on Saturday', the magical institute NIICHAVO faces the problem of resource shortages for experiments. Here, science solves the helium shortage with an elegant engineering solution, reminiscent of how characters in science fiction circumvent environmental constraints.