Want to get things really cold? You need cryogenics.
Many magnets at the MagLab operate at temperatures below ambient. These mostly include the superconducting magnets such as the hybrid outsert and NMR magnets. These magnets need an environment close to absolute zero (typically 4.2 Kelvin, -452° F) to be able to carry the high electrical currents needed to produce the magnetic fields.
This important container protects people in the lab from Oxygen Deficiency Syndrome.
Dilution fridges owe their cooling power to the incredible element helium. This animation illustrates how dil fridges exploit the element's properties to make things very, very cold.
The National MagLab is known for its world-record magnets, like the 45-tesla hybrid magnet — the strongest on the planet.
But for some physics experiments, there’s another critical ingredient to good results: extremely cold temperatures. And thanks to a fancy cooling machine called the portable dilution refrigerator (dil fridge, or PDF, for short), the National MagLab is able to offer a potent combination of experimental conditions unique in the world.
This month, the PDF is set up in one of our magnets, allowing scientists to observe what happens to materials when they are under magnetic fields as high as 35 teslas and at temperatures just above absolute zero (-459 degrees Fahrenheit or -273 degrees Celsius).
Leveraging the cooling power of liquid helium, the PDF removes thermal energy from the materials the researchers are studying. “This allows scientists to see the physical properties of materials, such as quantized energy states and quantum phase transitions,” said MagLab physicist Hongwoo Baek, who is in charge of the apparatus.
“If you add magnetic fields,” Baek continued, “you will also see magnetic properties, such as magnetic phase transitions, and other detailed electronic features that are not normally shown at zero field, that can be utilized in future electronics and applications.”
The National MagLab is the only place scientists can throw that one-two punch of very high fields and very low temperatures.
“Many institutes have 20-millikelvin dilution refrigerators, and some have 35-tesla magnets,” said Baek, “but none of them can provide the experimental platform with 20 millikelvin and 35- to 45-tesla magnet together.”
The MagLab system offers another big bonus: it can rotate samples within the magnetic field without generating much heat, allowing the sample to align to the magnetic field and stay nice and cold.
Over the next few weeks, research groups from Rice University, Princeton University, Northwestern University, the University of Cambridge and the MagLab will conduct experiments in this unique setup, studying phenomena ranging from the fractional quantum Hall states to exotic magnetic phase transitions of various materials.
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Text by Kristen Coyne. Photo by Stephen Bilenky.
This week at the lab is pretty quiet. Most of the staff is off for the holidays.
But not Jesus Torres Camacho and Dan Freeman — because science never sleeps.
As we head into the first, and statistically coldest, month of the year (at least in Florida), Camacho and Freeman will be at the MagLab doing their part to keep things frosty.
The pair are members of the MagLab’s cryogenics team, making sure the lab’s scientists and magnets have enough liquid helium and liquid nitrogen to keep the experiments going. All the lab’s superconducting magnets require cryogens, as do many of the experiments run here: Scientists doing low-temperature physics often want to put their samples in a deep freeze (temperatures often just above absolute zero) in order to observe special phenomena. The lab uses about 435,000 liters (114,915 gallons) of liquid helium a year (much of which is recycled), and about four times as much liquid nitrogen.
That's where the cryogenics team comes in, converting helium from gas to a frigid liquid with our helium liquefier and helping distribute it across the 370,000-square-foot lab through an army of some 55 dewars — basically Thermoses on steroids and wheels — containing 100 to 500 liters (26 to 132 gallons) of the stuff.
On an average day, about a dozen scientists, technicians, postdocs or graduate students come to the lab’s "helium retrieval station," located in the DC Field Facility, to pick up a newly refilled stainless steel dewar, and wheel it through the hallways back to their experiments and instruments. It works out to about 1,200 liters (317 gallons) of helium a day.
Text by Kristen Coyne
These bags are part of a recovery project that helps control the lab's helium bill.
35 tesla magnets. Unfortunately, that happened to coincide with the International Cryogenic Materials Conference (ICMC) taking place in New Delhi, India, where Iida was slated to receive the ICMC Cryogenic Materials Award for Excellence. It was one of those “must be present to win” situations: Officially, scientists selected for the honor must attend the conference. But Iida was loath to forgo the magnet time for his experiment, "Jc and Hc2 characterizations of P-doped Ba-122 thin films on IBAD-MgO tape in high field."Kazumasa Iida had a bit of a conflict this week. A professor in the Graduate School of Engineering at Japan’s Nagoya University, he was scheduled for magnet time with one of the National MagLab’s
Luckily, where there’s a problem, MagLab engineers are bound to find a solution, as was the case with this scheduling conundrum. MagLab engineers Bob Walsh and Eric Hellstrom orchestrated and videotaped a mini awards ceremony this week at the MagLab that was broadcast at the conference plenary talk in New Delhi, a creative solution that conference sponsors readily accepted.
The award recognizes an individual, usually under the age of 40, for excellence in advancing the knowledge of cryogenic materials over recent years. Iida is the second researcher to be honored by the award since it was launched in 2014. The first to win the award was Fumitake Kametani in the Applied Superconductivity Center at the MagLab.
This week at the lab, engineers are busy refurbishing a one-of-a-kind magnet that drove another set of researchers so crazy they stopped using it a decade ago.
But one scientist's trash is another's treasure, and instead of landing in the dumpster, the 20-year-old, 16 tesla magnet ended up at the MagLab, in the hands of some very patient problem-solvers.
The machine is a magnetic levitation apparatus, specifically designed to levitate drops of liquid helium, an important cryogen that must be extremely cold (at least -452 degrees Fahrenheit, or -269 degrees Celsius) to remain a liquid.
By levitating liquid helium, scientists can study how it behaves in space, where weightless astronauts float and liquids form drops held together by surface tension. By continuously simulating zero gravity, the magnetic levitation apparatus could help scientists understand how to better control liquid fuels in space and how to operate superconducting magnets, which require liquid helium, on space stations.
Saving the complex apparatus from the science graveyard has demanded the tenacity and ingenuity of the lab's Cryogenics Research Group. Postdoctoral researcher Mark Vanderlaan and graduate research assistant Andrew Wray have spent the better part of a year figuring it out without the guidance of the long-lost operational manual.
After months of trial and error learning all the parts and their functions, the MagLab engineers had to deal with another huge problem: finding and plugging dozens of leaks. It was a lot harder than locating holes in a bike tire: Helium is the second smallest atom in the universe.
"It likes to leak out of anything," said Vanderlaan. "It was obvious why the person gave up on it before."
Getting the magnet operational will require a lot more work, but knowing the result could be a unique and valuable tool for both basic and applied research is pretty good motivation.
Photo by Stephen Bilenky, text by Kristen Coyne.