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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, 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.
This week at the lab, we retired a 1990 Toyota and are parking a 2016 Mercedes in its spot.
That's the metaphor offered by Bryon Dalton, head of operations for the lab's DC Field Facility, for a big upgrade of the lab's world-record 45 tesla hybrid magnet: a new set of 3,500-pound vacuum pumps.
Good-bye roll-down windows and Bush Sr.-era fuel economy. Hello turn-by-turn navigation, Bluetooth wireless data link and 10-way power driver seat.
The $260,000 German-made vacuum pumps will improve reliability and performance, generate systems diagnostics, and allow staff to run the pumps remotely. "You're going to have a better feel for what's going on and better control over it," said Dalton.
The pumps play a critical role in the operation of the hybrid, which pairs a resistive magnet with a superconducting magnet of niobium-tin and niobium titanium that requires temperatures near absolute zero. Helium liquefied on site has a temperature of 4.7 Kelvin, making Plutonian weather seem tropical by comparison. By dropping that liquid helium to below atmospheric pressure, the vacuum pumps, used with a special cooling apparatus called a Joules-Thompson refrigerator, gets it down to 1.6 Kelvin. This turns it into a zero-viscosity "superfluid" and maximizes the hybrid's efficiency.
Photo by Stephen Bilenky, text by Kristen Coyne.
A helium-recovery project means major savings — and more focus on science.