At the APS March meeting, researchers unveiled a system for small labs that conserves helium used to cool delicate equipment.
Catherine Bruzak March 15, 2024
Credit: Liya Bi / UCSD
The parts for the helium recovery system designed by Shaowei Li's team cost about $100,000. This is a significant reduction from the millions of dollars that a large commercial system would cost.
Helium may be the second most abundant element in the universe, but it is a finite, non-renewable resource on Earth. Helium is so light that it cannot be trapped in the lower layers of Earth's atmosphere. They are also very difficult to capture due to their relatively low reactivity. Liquid helium is a key component in cooling systems used to study quantum systems and image atoms, as well as in high-performance magnets used in MRI scanners and particle accelerators. However, if helium is not carefully contained, when it boils it can travel to the ends of the atmosphere or even into space.
Xiaowei Li, a chemist at the University of California, San Diego, said he has become increasingly aware of the value of helium in more than a decade of working with equipment that requires supercooled conditions. During that time, he has seen the price of liquid helium rise from about $2 per liter to $20 per liter.
So Lee decided to take matters into his own hands and build a system to condense and recycle helium in his lab. At APS's March meeting in Minneapolis, Riya Bi, a graduate student working with Lee, explained how they did it. Using a combination of air compressors, brewing equipment, and hardware store-purchased parts, the UCSD team has created a relatively easy-to-use system that can recover 92% of the liquid helium used in the lab without creating vibrations that would shock sensitive equipment. We created an inexpensive system.
Helium is produced by the radioactive decay of underground elements and is often mined in the same locations as natural gas. But human use of helium is increasing faster than it can be replenished through natural processes, Lee said. Geopolitical and economic turmoil is putting at risk scientists' ability to maintain a stable and affordable supply. Under the terms of a 2013 law, the United States, the world's largest producer of the critical element, could sell its helium reserves, pipelines and wells to private companies later this year. The impact of this sale on researchers is unclear.
Liquid helium, which has a cold boiling point just a few degrees above absolute zero, cools lithium scanning tunneling microscopes (STMs), which use razor-sharp tips to image and manipulate single atoms on surfaces. It is essential to Because atoms must be stationary, they require very low temperatures to operate. “Thermal perturbations can throw off the measurements,” Lee says. His lab uses STM to study the quantum states of single atoms. This is key to understanding the driving forces underlying chemical reactions. “To study quantum systems, you need to make the surroundings as cold as possible,” he says.
Over the past decade, companies have developed systems to conserve liquid helium. But these systems don't work in labs like Lee's. That's because they cost more than $10 million and are intended for systems that use large amounts of liquid helium, designed to liquefy around 100 liters per day. Therefore, they are typically shared between multiple laboratories or medical imaging bays. Lee's lab doesn't have pipes to connect to either of these systems. He points out that the university hospital is across the highway from his lab. Other options vibrate too much to share space with his sensitive STM.
“Helium is becoming increasingly expensive and difficult to manage,” says Paul Weiss, a chemist at the University of California, Los Angeles. Weiss also uses scanning tunneling microscopes, and says helium is a big expense for labs that operate these microscopes. These setups are highly sensitive to vibrations, he says, which typically makes helium recovery systems difficult or inefficient to implement.
Lee's group made the helium recovery system work by separating the noisy parts of the helium storage system from the STM. The helium evaporated from the STM's cryostat is piped to another room, where it's safe from the vibrations of a noisy air compressor. The gas is condensed on a cooling coil (usually used to cool beer) that Lee buys from a brewer and stored in a metal container called a dewar. The most expensive part was the capacitor, which cost about $70,000. Lee said the entire system cost about $100,000 to build, but he expects that cost to be recouped in helium savings within two years. Li's group describes their design in a preprint submitted to arXiv in January of this year.
Credit: Liya Bi / UCSD
Li's group described their design in a preprint submitted to arXiv in January of this year.
Lee is a chemist by training, but says this kind of DIY work is never far away for him. He likes making new instruments. Most of his work is devoted to building new imaging technologies. At the March conference, Lee also talked about his own 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. Ta. He said the work was inspired by his Ph.D. His advisor, Wilson Ho of the University of California, Irvine, often said that if what he needed didn't exist, he should try to create it.
Weiss called Li's helium recycler a “smart integrated solution” that allows the UCSD team to collect high-quality STM data even when the system is turned on, allowing small labs to work with this sensitive equipment. He says he's proving it can be done.
Lee says the helium recovery design could also be implemented in other small labs that house sensitive equipment. The research team has applied for funding from the National Science Foundation to further develop the system.
Katherine Bruzak is a science writer based in San Francisco.