Synopsis: Get the Hydrogen Out

Using clean helium made with a two-step purification process could prevent damaging blockages in cryostats.
Synopsis figure
M. Gabal et al., Phys. Rev. Applied (2016)

Liquid helium is the unsung partner in numerous low-temperature experiments. Unfortunately, the cryogen is expensive. So to preserve it, a growing number of labs have liquefiers, which collect evaporated helium and cool it back into liquid. Conrado Rillo, of the University of Zaragoza, Spain, and the Spanish National Research Council, and his colleagues have now developed a “clean helium” recipe for liquifiers that should prevent a costly problem for cryogenic experiments: blockages caused by solidified hydrogen molecules.

For certain low-temperature applications, researchers need a cryogen that’s colder than standard liquid helium (4.2 K). Pushing helium through a narrow capillary such that it cools upon expanding at the exit can chill the liquid to 3 K and below. But at these temperatures, molecular hydrogen (H2)—a common impurity in helium that is tough to remove—almost completely solidifies. Rillo and his co-workers thought that H2 collecting on the capillary walls might explain numerous reported failures in cryogenic experiments. To test their hypothesis, they pumped helium through a pinched capillary. Within 10 hours the thin tube had a clog, which only cleared when the tube was warmed above H2’s melting point.

The researchers estimate that, to prevent blockages, the H2 concentration has to be roughly ten million times lower than that of commercial grade helium. To reach this purity, they propose a two-step solution: a pre-freeze that condenses out the H2 (and other impurities) and the use of a getter purifier, which absorbs the remaining H2. They produced this clean helium at the University of Zaragoza’s helium liquefaction plant, and using it kept their cryogenic instruments blockage-free for more than a year.

This research is published in Physical Review Applied.

–Jessica Thomas

Jessica Thomas is the Editor of Physics.


Features

More Features »

Announcements

More Announcements »

Subject Areas

Industrial PhysicsStatistical Physics

Previous Synopsis

Next Synopsis

Quantum Physics

A Tight Squeeze

Read More »

Related Articles

Focus: Identifying Early Signs of Online Extremist Groups
Complex Systems

Focus: Identifying Early Signs of Online Extremist Groups

An analogy between the growth of online networks and the formation of gels suggests ways to detect extremist groups before they become influential. Read More »

Focus: Glue or Ink Improves Soft Metal Cuts
Industrial Physics

Focus: Glue or Ink Improves Soft Metal Cuts

Coating a soft metal with any compound that adheres leads to smoother cuts because the coating makes the surface more brittle. Read More »

Viewpoint: A Toy Model for Active Interfaces
Biological Physics

Viewpoint: A Toy Model for Active Interfaces

A new statistical model predicts the evolving shape of a cellular membrane by accounting for the active feedback between the membrane and attached proteins. Read More »

More Articles