An Inexpensive, DIY Setup Recycles Precious Liquid Helium in the Lab

Helium may be the second-most abundant element in the universe, but on Earth it’s a finite, nonrenewable resource. Helium is so light that it’s not trapped by the lower levels of Earth’s atmosphere. And it’s extremely challenging to capture, since it’s relatively unreactive. Liquid helium is a critical ingredient in systems for cooling equipment used to study quantum systems and image atoms, as well as in the high-performance magnets used in MRI scanners and particle accelerators. But if it is not carefully contained, helium flies to the farthest reaches of the atmosphere or even out into space when it boils.

Shaowei Li, a chemist at the University of California, San Diego, says the preciousness of helium has become increasingly clear to him in over a decade working with instruments that require supercool conditions. Over that time, he’s seen the price of liquid helium rise from about $2 per liter to $20 per liter.

So Li decided to take matters into his own hands and build a system to condense and recycle helium in his lab. At the APS March Meeting in Minneapolis, Liya Bi, a graduate student working with Li, described how they did it. The UCSD team combined an air compressor, brewery equipment, and parts from a hardware store to make a relatively inexpensive system that can recapture 92% of the liquid helium used in their lab — without creating vibrations that would jar sensitive equipment.

Helium is generated by radioactive decay of elements underground, and it’s often mined in the same places as natural gas. But humans are using helium at a growing rate, faster than natural processes can replenish it, says Li. Geopolitical and economic turmoil have jeopardized scientists’ ability to sustain a steady, affordable supply. Under the terms of a 2013 law, the United States — the world’s biggest producer of this critical element — may sell the country’s helium reserves, pipelines, and wells to a private company later this year. The impact of this sale on researchers is not clear.

Liquid helium, with its chilly boiling point only a few degrees above absolute zero, is critical for cooling down Li’s scanning tunneling microscope (STM), which uses an extremely sharp tip to image and manipulate single atoms on a surface. It requires very cold temperatures to operate, as those atoms must hold still. “Thermal perturbations will mess up the measurements,” says Li. His lab uses an STM to study the quantum states of single atoms, which are key to understanding the underlying drivers of chemical reactions. “To study quantum systems, the surrounding has to be as cold as possible,” he says.

In the last decade, companies have developed systems for conserving liquid helium. But those systems don’t work for labs like Li’s. That’s because they cost upwards of $10 million and are intended for systems that use large amounts of liquid helium, designed to liquify about 100 liters a day. So they’re typically shared between multiple labs or medical imaging bays. Li’s lab doesn’t have pipes connecting them to one of these systems — the university hospital, he notes, is across the freeway from his lab. Other options vibrate too much to share space with the sensitive STM.

“Helium is getting increasingly expensive and difficult to manage,” says Paul Weiss, a chemist at the University of California, Los Angeles. Weiss also uses scanning tunneling microscopy, and he says helium is a major expense for labs operating these microscopes. These setups are extremely sensitive to vibrations, which typically makes helium recovery systems difficult or inefficient to implement, he says.

Li’s group made a helium recovery system work by separating the noisy part of the helium conservation system from their STM. Helium that boils off the STM’s cryostat is piped into another room, where a noisy air compressor can vibrate without causing problems. The gas is condensed on a cooling coil that Li bought from a brewing supplier — typically used to cool beer — and stored in a metal container called a dewar. The most expensive part is the condenser, which was about $70,000. Li says the entire system cost about $100,000 to build, and he expects to recover the costs in saved helium in two years. Li’s group describes their designs in a preprint submitted to arXiv this January.

Though he’s a chemist by training, Li says this kind of DIY work isn’t too far afield for him. He enjoys building new instruments. A large part of his work is dedicated to building new imaging technologies. At the March Meeting, Li also talked about his work on what he calls hyperdimensional scanning tunneling microscopy, which can provide high-resolution information about the movement of electrons in space and time in response to laser pulses. He said this work is inspired by his Ph.D. advisor, Wilson Ho of the University of California, Irvine, who used to tell him that if something you need doesn’t exist, you should try to build it.

Weiss calls Li’s helium recycler “a clever integrated solution,” and notes that the UCSD team is still able to collect high-quality STM data with the system turned on, proving that it can work alongside this sensitive equipment in a small lab.

Li says it should be possible to implement the helium-recovery design in other small labs that house sensitive equipment. The team has applied for funding from the National Science Foundation to further develop the system.