SCIENCE, DISCOVERY & MAGNETISM
Scientists have big ideas. Now they need stronger magnets. CARBON IN THE CONGO
African river contains clues to carbon cycling worldwide
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Once faint atomic signals come thru loud and clear Brought to you by the National MagLab
Carbon in the Congo The storied African river contains clues to carbon cycling worldwide.
DNP Is Having a Moment With the help of dynamic nuclear polarization, once faint atomic signals come through loud and clear.
Magnet Mystery Is there enough zinc in my toothpaste? DNP comes to the rescue.
Fields of Dreams
If engineers build stronger magnets, scientists promise to come â€Ś and to use them for far-reaching discoveries.
fields is produced at the National High Magnetic Field Laboratory (National MagLab) with the support of scientists around the world. Our goal is to show both doers and lovers of science some of the very cool things researchers discover about our world using high-field magnets.
The Long Winding Road Several designs are in the running to build the next generation of superconducting magnets. Which will win the honor?
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Area residents watch as Florida State University graduate student Travis Drake collects water samples from a stream in the Democratic Republic of Congo. Photos by Adam Amir
the Congo Rob Spencer collects water samples from the heart of Africa to learn more about global carbon cycling worldwide. By Abigail Engleman
he Congo River Basin remains relatively pristine, in an untouched state similar to the Mississippi 200 years ago or the Amazon 100 years ago. Its vast tropical forests have been protected from human impacts by political instability and a lack of infrastructure. To those gutsy enough to conduct research there, the understudied region is a frontier for scientific discovery — a window into an undisturbed carbon cycle and a glimpse of what the planet’s other great rivers looked like before the impact of civilization. Rob Spencer, a biogeochemist at Florida State University who has studied carbon cycling in some
of the world’s other great river systems, never intended to extend his research to Africa. But when Spencer made a comment about the understudied Congo River during a lecture, a fellow scientist challenged him to study it. He decided: Why not? “What’s the worst that could happen?” he thought. Before he knew it, he was deep in the Congo, collecting water samples in one of the most challenging and inaccessible environments on Earth. He and his team have had countless obstacles, adventures and life-changing experiences along the way. fieldsmagazine.org
“When people hear you work in the remote tropics, their initial thought is of tropical diseases. And yes, there are challenges that go along with that,” says Spencer. “But I actually think that, to this day, one of the biggest challenges in some of the places where we work is just getting food — and this is a challenge a big part of the local population faces every day.” The Democratic Republic of Congo (DRC), where many of Spencer’s field sites are located, has long been politically unstable. “You need the right local collaborators to facilitate access to the sites where we work,” says Spencer. Working with local scientists was essential to maneuver the sporadic chaos that can easily occur, especially in remote locations. There has been no shortage of “moments of excitement,” as he calls them, in the DRC. “The Congolese have been some of the most welcoming and friendly people to work with,” Spencer says. They also understand that Spencer’s research could improve their water quality and the productivity of their soils. Just as doctors take blood samples to assess a patient’s health, Spencer’s water samples are a measure for how deforestation and agriculture affect local and global carbon cycling. “What happens in the Congo, doesn’t stay in the Congo,” explains Spencer. “The forests, swamps and soils of the Congo River Basin can be thought of as a giant tea bag that is leached by rain, resulting in an organic, rich tea that ultimately flows out to the ocean.” With the second largest water volume of all rivers, draining the world’s second largest rainforest, this river plays an important role in moving a lot of carbon to the ocean and atmosphere. Deforestation and agriculture can influence the quantity, timing and form of carbon transferred from land to ocean, and ultimately atmosphere. Previous carbon models have extrapolated data from the
Amazon to explain global processes, oversimplifying and underestimating the influence of other tropical regions such as the Congo. Spencer brings his water samples back to the National High Magnetic Field Laboratory to fill this knowledge gap. The MagLab is home to the world’s strongest ion cyclotron resonance magnet, which Spencer uses to create high-resolution “fingerprints” of filtered water samples that reveal tens of thousands of different kinds of molecules in the water. These organic markers create unique signatures that serve as a health index for the ecosystem and provide evidence of the impact of deforestation and agriculture, which are becoming more widespread in the region. Conversion of pristine lands to agriculture impacts not just the quantity but also the quality of the river’s carbon, and ultimately its role in the global carbon cycle. The challenging environment and preconceived notions of what life is like in the Congo are enough to keep many researchers at bay. Spencer sees the humid rainforest, muddy roads, crowds of people and other inherent difficulties of working in a developing country as a small price to pay for unlocking the Congo’s wealth of knowledge. Despite the dichotomy between the region’s lack of infrastructure and the high-tech facilities at the MagLab, exploring this scientific frontier is a twoway street, Spencer says. “As much as we provide access to advanced analytical techniques here at the MagLab, our Congolese colleagues educate us about how the system is transitioning and the pace of this change,” he says. “We are building a partnership to bear witness to this impact together, and that’s one of the beautiful things about this. The next step is to hopefully do something about it.”
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A technique called dynamic nuclear polarization is hitting its stride, using electrons to shine a light on complex molecules.
here was darkness. Then dimness. Then, at last, there was light.
In the era before nuclear magnetic resonance (NMR), scientists trying to map out complex molecules like proteins had few tools to work with. Then, in the 1950s, the first NMR commercial instruments came online. Using magnetic fields and radio waves, the revolutionary technique shone some light on those molecular mysteries, identifying atoms and how they fit together. The problem was, NMR worked better detecting some atoms than others. And even the “easy” atoms took days, sometimes months to sort out, due to their relatively weak signals. Then came the dawn of DNP. For decades scientists have been developing dynamic nuclear polarization, or DNP, to address NMR’s shortcomings. Now, thanks to the availability of higher magnetic fields and the tenacity of DNP pioneers, researchers can see molecule-level structures and processes in unprecedented detail and at astonishing speeds. “We had to iron out the nitty-gritty hardware stuff,” said Joanna Long, director of a facility devoted to NMR, magnetic resonance imaging (MRI) and DNP experiments at the National High Magnetic Field Laboratory. “We kind of waded through our Dark Ages. And now we’re in the Renaissance. Suddenly, we know how to handle the technology and use it for all kinds of good things.”
An increasing number of commercial DNP instruments can now be found in labs and hospitals around the world. Scientific publications that reference the technique have increased more than sixfold in the past decade. Researchers are regularly discovering new uses for DNP, probing brain metabolism (as Long’s group does), outwitting fungal infections, even making sure your toothpaste is doing its bacteria-killing job (see infographic on page 12). DNP, clearly, is on a roll. There are still plenty of details to figure out, DNP developers say, and some approaches are advancing more smoothly than others. But for newcomers willing to tweak experiments and reshape their questions, the technique promises to unlock all kinds of science mysteries.
DNP: A tale of two signals DNP is NMR on steroids. It boosts the pianissimo signals of the atoms scientists want to tune into with the help of fortissimo electrons. Here’s how it works. NMR machines leverage a magnetic property inherent to the nuclei of all atoms called “spin” or “magnetic moment.” Thanks to spin, nuclei can align, or polarize, with or opposite a magnetic field. Combining that field with radio waves, NMR machines manipulate and read these alignments, which are exquisitely sensitive to the chemical environment. These quantum acrobatics send fieldsmagazine.org
signals to a detector to disclose the target atom’s whereabouts, helping scientists piece together a molecule’s structure.
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Many important biological elements, including carbon, are not particularly sensitive to this technique. Accumulating enough data to hear those faint signals can take weeks, even months, running up experimental costs. This is where DNP amps things up. When atoms have an odd number of electrons, that oddball — called an unpaired electron — has a lot more spin than a nucleus. So in DNP NMR, scientists add molecules called polarizing agents, which have these unpaired electrons, to the sample. Simply put, DNP polarizes those electrons first, then transfers that energy to the target atoms — a kind of domino effect. In this way, a far greater proportion of target atoms get polarized, resulting in a fortissimo signal that is orders of magnitude stronger than in conventional NMR. Bravo, DNP! Different DNP methods address different science questions. The first to generate big results in living systems was dissolution DNP. And Matt Merritt was among the initial scientists to use it. It was an experiment he’ll never forget.
Seeing what’s never been seen A decade ago, Merritt was a young professor studying heart metabolism at the University of Texas Southwestern Medical Center. His group there had acquired one of the first commercial dissolution DNP systems. In this kind of DNP, scientists initially polarize atoms in a solution, then inject that solution into an animal or tissue sample placed inside an MRI machine (MRIs are a kind of NMR machine). Then they observe what happens as the substance is metabolized. In Merritt’s first foray into DNP, he injected polarized acetate into the heart of a rat. (When not immediately used for energy, acetate gets stored by the body in the compound acetylcarnitine.) Merritt then went to his computer to observe the 8
Matt Merritt says DNP-based metabolic imaging will transform medical science in the next few years. signals. In NMR experiments, data appear on a screen in a series of peaks (similar to those on a heartbeat monitor), each denoting the presence of a particular compound. “Then this peak just popped up,” remembered Merritt: It was the molecular fingerprint of acetylcarnitine. He had just watched a heart put acetate in storage … while it was actually happening. “I’ve never seen that before,” Merritt thought as he stared. “Nobody has ever seen that before.” Now an associate professor of biochemistry and molecular biology at the University of Florida (UF), Merritt is quite used to seeing things never before seen. Dissolution DNP has mushroomed, with more than 50 systems worldwide, including about 20 used for human patients in hospitals. Merritt uses the National MagLab’s DNP system at UF to study metabolism in the liver. Specifically, he looks at the chemical reactions the body uses to release stored energy, known as the Krebs cycle. After polarizing the carbon in the compound dihydroxyacetone (DHA, or C3H6O3), he injects it into the liver of a mouse and measures the metabolic uptake and disposal of the agent. This provides unprecedented insight into both glycolysis and Krebs cycle metabolism. There, the compound does one of two things, Merritt has observed: It gets turned into glucose for immediate use in the body, or it’s drawn into the
Krebs cycle, where it helps make the energy-storing molecule ATP for other liver functions. Merritt hopes the discoveries he is making will shed light on why nonalcoholic fatty liver disease, which is relatively harmless, sometimes leads to nonalcoholic steatohepatitis (NASH), a serious condition projected to become the main cause for liver transplants in the next 20 years. “Hopefully,” Merritt prognosticated, “we can develop some kind of imaging exam that would say, ‘Hey, you’re on the verge of developing NASH. We need to intervene immediately.’” Other kinds of metabolic imaging might one day help detect cancer cells (which could become visible after metabolizing polarized glucose into lactate) and warning signs of a heart attack (energy metabolism changes when the heart is stressed). “We are within five years of using DNP-based metabolic imaging to transform medical science,” Merritt continued. “We just don’t know exactly how — yet.”
Spin doctors Another approach to DNP, called MAS DNP, helps scientists unravel the molecular structure of complex solids, such as proteins. The Ph.D.’s behind these experiments are true spin doctors. MAS stands for magic angle spinning, and refers to a special rotor inside the magnet that whirls the proteins (or other samples) around thousands of times a second, a necessary trick for getting the right signals from most solid samples. MAS DNP has boomed since Bruker Corp. put the first commercial instrument on the market in 2009. By mid 2018, more than 30 were in use worldwide. One is at the National MagLab, where scientists like Tuo Wang of Louisiana State University come to learn the ropes from the experts. What has Wang been taking for a spin? Fungi, which are responsible for infections that claim more than 1.5 million lives a year worldwide.
In conventional NMR, researchers usually look at purified samples, extracting from cells just the molecules they’re interested in. But for his research, Wang needs a more realistic picture. To better understand the cell wall structure, he studies the interactions between lignin and cellulose there and what happens to carbon in the molecules at that interface. This requires looking at the cells in situ. Because the target atoms are fewer and farther between in this native environment, scientists need the sensitivity of MAS DNP to see them. Wang is the first to look at the whole cell of this system in its native state at such high resolution, he said. He was able to collect data so quickly this year that he already has one publication on the topic under his belt, and several more in the pipeline. His team’s next step with DNP: Expose the fungus to different drugs. “We’ll see how the drugs really react in the cell,” Wang said, “and we’ll see what kind of molecular insight we can provide to design better drugs.” Every new application means new issues to troubleshoot, said Fred Mentink-Vigier, a physical chemist who runs the MAS DNP program at the National MagLab. For Wang’s experiments, for example, Mentink-Vigier had to figure out how to turn off the microwaves while taking measurements in order to remove unwanted signals.
A lone voice gets heard If that sounds hard, imagine building the first MAS DNP instruments from scratch. That was the job of one of the original spin doctors, MIT chemist Robert Griffin. In the mid 1980s, Griffin was studying a protein called bacteriorhodopsin, found in the retina. In a remarkable sequence of steps scientists were (and still are) keen to better understand, the protein uses energy from a photon of light to initiate a nerve impulse. “Understanding how a biological system works so efficiently is something that is of tremendous interest,” said Tim Cross, director of the NMR facility at the National MagLab. “If we could fieldsmagazine.org
: a mi g n a l ! ! h w s
Tuo Wang (left) and Fred Mentink-Vigier study the cell walls of fungi. Photo: Stephen Bilenky
harness this technology for an energy source, it would be fantastic. And bacteria have been doing this for millennia.” When Griffin tried conventional NMR to study how ions were crossing cell membranes during this photocycle, he got a lot of noise in his data. It’s like trying to listen to a song on your car radio when the station is out of range: You’re picking up signals, but the static makes it hard to hear the music. “We did a lot of experiments without DNP,” remembered Griffin. “But it became very apparent very, very quickly that if we had a big signal-tonoise enhancement technique, and we could do spectroscopy at low temperatures, we could learn a lot more about the system.” That turned out to be a pretty ambitious “if.” MAS DNP didn’t exist yet. He would have to build it. Some doubted it could be done, but Griffin was in it for the long haul. “He was the lone voice saying it was going to work out and it was going to be great for everyone,” recalled Joanna Long, a former graduate student of Griffin’s. There were plenty of hurdles, including building a gyrotron to generate the frequency of microwaves his set-up required. But eventually it paid off with an instrument that could detect the subtle signals of the carbon, nitrogen and hydrogen he was trying to map. Today, Griffin’s lab at the Francis Bitter Magnet Laboratory boasts several home-built DNP systems. Now when Griffin examines the bacteriorhodopsin 10
photocycle using MAS DNP, very cold temperatures and lasers of different colors, he can capture incredible details at specific stages that shed light on how hydrogen crosses cell membranes. “What we’re interested in is how this proton pump works, how this inward-directed hydroxyl pump works,” Griffin said. “And in order to understand that, we have to trap various intermediates in this photocycle.” The MAS DNP improved the signal-to-noise ratio by a factor of 75, Griffin said, making the experiment thousands of times faster. “It’s an enormous time savings,” said Griffin, who also uses MAS DNP to study the amyloid protein fibers associated with neurodegenerative disease. “You just couldn’t do these experiments without this increase in sensitivity.”
Prepping samples isn’t simple While dozens of commercial instruments are in use worldwide for dissolution and MAS DNP, a third DNP technique, Overhauser DNP, has proven a tougher puzzle. But when those pieces come together, it will fill a vast void by allowing scientists to study molecules in liquids at low concentrations. Several teams around the world are developing the technique. At the National MagLab, physicist Thierry Dubroca has devoted several years to assembling a machine and getting it to work. But that may have been the easy part.
! A MR H E R O Z A S H UPE
A S PLE! IT’S SAM
Elzbieta Miegel combines a polarizing agent, solvent and target molecules in a tube for an Overhauser DNP experiment. Matching polarizing agents to the right solvents is a tricky process. Photo: Stephen Bilenky
“We have a good instrument,” Dubroca said. “Now we need good samples.” Easier said than done, it turns out. Preparing good samples for Overhauser DNP requires savvy chemical matchmaking: You need to pair the sample with the right polarizing agent, which itself must be paired with the right solvent. To assist with this challenge, Dubroca recently recruited chemist Elzbieta Miegel of the University of Warsaw, who designs and assembles polarizing agents for other applications. All polarizing molecules feature at least one unpaired electron, which is the electron used to transfer spin to the target nucleus. Through some educated trial-anderror, Dubroca and Miegel have learned more about which polarizing agents work well for Overhauser DNP, and which solvents work well to dissolve those molecules into the sample. “It’s a very small step, but it’s critical,” Dubroca said. “It does not allow you to publish a paper. But you need that as one of the many little steps before you can even do the science that will give you a paper.” Eventually, Dubroca said, Overhauser will generate plenty of journal articles. Once up, running and debugged, he believes it will make thousands of molecules in biological samples visible to scientists, a huge leap over the 100 or so accessible via NMR today. One day, he envisions, doctors could
even use Overhauser DNP right in their offices to diagnose patients by differentiating between “sick” and “healthy” levels of molecules in the body. Dubroca has a lot to figure out between now and then. “That’s how science works,” he said. “We’re trying really hard to get the liquid DNP figured out and then the next stage is to make it user friendly.” In the meantime, more and more scientists are discovering DNP’s power. One colleague described the experience to MIT’s Griffin last year as a “DNP moment.” “That’s a moment when you do an experiment that you’ve tried to do for years, but you didn’t have enough signal-to-noise to do it,” Griffin recounted. “And all of a sudden — wow — this huge signal pops out at you in a very short period of time.” It’s what you might call seizing the moment — the DNP moment. Science advisor: Kendra Frederick.
Want to see dynamic nuclear polarization in action? Turn the page.
m a gn et m y s t e r i ePsA
The case of the Zinc in the toothpaste the It’s a tough case to crack: The Zinc in the toothpaste must be active in order to kill bacteria. But Zinc’s signal is too weak to detect.
This is a job for secret Polarizing Agent! The mission: Make Zinc stronger so scientists can see it.
The magnetic field and some microwaves energize PA. Zinc, in the meantime, remains weak.
Polarizing Agent infiltrates the scene, joining Zinc in a magnet.
PA then transfers its polarizing energy to Zinc. Wow, thanks, Polarizing Agent!
After the microwave and magnetic field are turned off, Zinc releases that energy in the form of a strong signal that is picked up by the detector.
meh . PA
Without thePAhelp of PA, Zinc’s signal would be too weak. PA
Giving weak atoms a strong voice in the name of science: Just another day at the office for secret Polarizing Agent
But thanks to PA, Zinc’s signal comes across loud and clear. Scientists can see exactly where Zinc is and how Zinc relates to other atoms in the toothpaste.
Illustration: Caroline McNiel Science advisor: Thierry Dubroca
The world is full of mysteries. Scientists want to solve them. They have the dreams. They have the will. Now they just need the tools to make the discoveries lying beyond their reach. What could scientists find with higher fields? Turn the page. How do you build a record-breaking magnet? See page 18. STORIES BY KRISTEN COYNE
S D L E I F AMS E R D OF
If engineers build stronger magnets, scientists promise they will come … and that discoveries will follow. eike Kamerlingh Onnes never would have discovered superconductivity back in 1911 if he hadn’t first learned to make liquid helium, which created the frigid temperatures the phenomenon required. In the 1950s, scientists wouldn’t have discerned the double helix hiding inside DNA if the X-ray diffractometer hadn’t first been invented. And those gravitational waves that were all over the news in 2016? You can thank the $1 billion (and counting) Laser Interferometer GravitationalWave Observatory for making that science milestone possible. Some of science’s biggest blockbusters remain hidden until the right tool comes along. That’s why scientists dream of stronger, faster, further and, in the case of magnetic fields, higher. Physicists exploring electrons, chemists decoding complex molecules and biologists scanning brain cells are clamoring for next-generation instruments. The U.S. National Academy of Sciences has advocated for them for years. 14
The next big magnets are overdue: The world’s strongest continuous-field magnet (the 45-tesla hybrid at the National High Magnetic Field Laboratory) has held the title for two decades. A few slightly stronger instruments are slated to come online in coming years, but those are merely hops forward. Scientists want leaps. They may soon get them. Thanks to recent advances in magnet technology, strategic government funding and the nudge of international competition, the momentum for higher fields may have reached a critical point. Scientists have been dreaming of them. And they are ready.
NEW PEAKS IN PHYSICS
Pulsed magnets are the most powerful kind of magnet (although, unlike continuous-field magnets, they can only operate for a fraction of a second). The strongest of them all, located at the National MagLab, reaches 100 teslas — for about 25
We’ve clearly identified an area of physics that we don’t understand and where magnetic field is having a profound role. Ross McDonald
milliseconds at a time. Physicist Ross McDonald wants to see it climb higher. McDonald, deputy director of the lab’s Pulsed Field Facility, co-authored a paper in the prestigious journal Science this year that reported a new phenomenon in a type of high-temperature superconductor (HTS) that could be observed only with the help of very high fields. Eighty teslas were needed to suppress superconductivity in the material, which revealed a different conducting behavior new to science. “We’ve clearly identified an area of physics that we don’t understand and where magnetic field is having a profound role,” McDonald said. “And we need these extreme fields of 100 teslas or more to look at this.” But magnets have not kept pace. The most robust HTS materials keep superconducting even in very high magnetic fields — higher than the strongest magnets available today — making it impossible to probe their “normal” conducting states. Yet such experiments are critical for understanding hightemperature superconductivity, one of the hottest areas in physics. That’s why the National MagLab is brainstorming magnet designs that could boost millisecondduration pulsed fields significantly. “Given the resources, our designs for magnets exceeding 130 teslas could be a reality within the decade,” McDonald said. To physicist Tim Murphy, director of the National MagLab’s DC Field Facility, findings like McDonald’s are tantalizing indications of what awaits when the continuous-field magnets he oversees make their next big leap past 45 teslas. “At pulsed fields, you see hints of physics that you
need more time, and a quieter environment, to study,” said Murphy. “And that’s what a 60-tesla DC magnet can provide.” That’s the lab’s longer-term target. To get there, lab leaders plan to first design and build a 40-tesla magnet featuring high-temperature superconductors (see story p. 18).
DISCOVERING NEW TIPPING POINTS
For Elizabeth Green, those high fields can’t come soon enough. A physicist at the Dresden High Magnetic Field Laboratory, Green is eager to put samples of lithium copper vanadate, a compound that may have electronic properties similar to liquid crystals, into continuous fields of 50-plus teslas. At that field strength, she dreams of studying a magnetic state that might be used to develop new electronic devices. “That would allow us to further probe and, with any luck, definitively prove the existence of the spin-nematic state in condensed matter systems,” explained Green. Physicists like to expose materials to extreme pressures, temperatures and magnetic fields to see what happens to them. Of these environments, magnetic field is particularly cool because you can point it in a specific direction, explained physicist James Analytis. That makes it really useful for probing anisotropic materials, which behave differently in a magnetic field depending on their orientation, said Analytis, an assistant professor at the University of California, Berkeley. So while the electrons in a material may behave like free electrons in one orientation, he continued, “if you tilt it and point it in another direction, you might find it behaves like a frozen particle, or a strongly interacting particle.” That’s the kind of powerful behavior that could one day be engineered into a switch. The stronger their magnets, the more scientists can leverage this vector advantage. Then there’s the matter of scale. Scientists already have a big temperature scale to play with, from near absolute zero to thousands of degrees Celsius. Making just the right tweak can cause fieldsmagazine.org
Higher fields could help physicists like Elizabeth Green prove new states of matter. quantum systems to break: At 0 degrees Celsius, for example, water turns to ice. Giving scientists access to a wider range of magnetic fields, Analytis said, could help them find similar tipping points that, by overcoming a system’s internal energy scale, could trigger a sudden change in behavior. “Sometimes,” Analytis said, “in order to understand that physics, you need to see how it breaks up.”
“We want to understand how the brain develops that circuitry, how it might actually grow new circuits, and how it might be affected by an injury,” Mareci said. “The only way to understand that without taking the brain apart is to look at it with high magnetic fields.” Thomas Budinger, a physician and physicist at the Lawrence Berkeley National Laboratory, is among those building a compelling case for a 20-tesla MRI. The instrument would probe questions that cannot be answered with other instruments, he said, including how neuron architecture is related to autism, obsessive compulsive disorders, schizophrenia, aging and chronic brain trauma. It could also identify small molecules associated with addiction, violence and depression.
HIGHER FIELDS FOR HEALTH
Budinger, who is also a professor at the University of California, Berkeley, where he has taught bioengineering, electrical engineering and radiology, said the ability to watch sodium cross cell membranes could teach scientists about bipolar disorder. The fact that lithium, an analog of sodium, is an effective treatment in many patients is one of many clues pointing in that direction, he said.
MRI machines identify hydrogen in the body, and sometimes other atoms, to create an image of different tissues that reveals tumors and other structures. NMR instruments work similarly, but examine specific tissue samples or molecules rather than whole bodies. The technique pinpoints the location and orientation of atoms so scientists can better understand, say, a protein’s structure or function.
“We could understand the sodium-potassium balance in the brain relative to mental states,” Budinger said.
Researchers in the health sciences use different kinds of magnets than physicists. Theirs are built with superconductors. For their nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) experiments, these scientists need fields that are both strong and uniform, which superconductors provide.
Stronger fields, scientists say, will help them see all this in greater detail as well as identify biologically important atoms that, until now, have escaped the reach of magnetic resonance. Scientists are proposing a 20-tesla instrument for human brain imaging and chemical detection — almost seven times stronger than a typical hospital 16
MRI and twice as powerful as the strongest MRIs used in human research. Its resolution would be 10 times what can be achieved today, said Thomas Mareci, professor of biochemistry and molecular biology at the University of Florida. In a square millimeter of brain tissue, he said, that’s the difference between seeing a lump representing tens of thousands of fibers and being able to identify each individual fiber.
A 20-tesla MRI could also shed light on another problem Budinger has worked on for decades: why some brain tumors resist treatment. “Since 1976 I have worked with the problem of treatment of this with neurosurgeons, and we have made zero progress,” said Budinger, “except to give patients quality of life in their last few years from diagnosis.” Studies have shown, he said, that tumor cells that metastasize produce lactate, unlike tumors that respond to therapy. With a strong enough MRI magnet, he continued, scientists could discern
current instruments aren’t sensitive enough to keep up with that pace.
With stronger NMR magnets, Harald Schwalbe will be able to understand, on the structural level, why drugs work. the difference and develop methods to measure and even modify the lactate-producing tissue, potentially revolutionizing cancer treatment.
“If we want to get real in these kind of things, I have to actually increase my sensitivity toward the speed at which cellular machines work,” said Schwalbe. “That’s another dream of NMR.” Yet another NMR dream is developing better pharmaceuticals. High-field NMR could not only show if a drug works, but also reveal details of its interaction with the target. “With these machines,” said Schwalbe, “we’ll be able to actually understand, on a structural basis, how come the drugs work the way they work.” A new NMR magnet at the National MagLab bodes well for Schwalbe’s dreams.
SCOPING CELLULAR SECRETS
While Budinger advocates for more powerful MRI magnets, over in Germany, Harald Schwalbe has campaigned for record-breaking NMR machines, which get clearer signals from atoms with higher fields. He is close to achieving that dream. The German government has funded several NMR magnets that will, when delivered, be the most powerful to date, with field strengths of 28.2 teslas. NMR magnets are more commonly referred to by their frequency — in this case, 1.2 GHz, which is the resonant frequency for hydrogen atoms at 28.2 teslas. One of the new 1.2 GHz instruments, which are being built by Bruker Corp., will land at the Goethe University Frankfurt, where Schwalbe is a professor of chemistry and biochemistry. Over the years, Schwalbe has watched more NMR science emerge with each jump in strength, from 600 MHz to 800 MHz to, most recently, 900 MHz, which, as Schwalbe put it, broke a “size barrier” that allowed scientists to probe the largest of proteins. “Now the question is,” Schwalbe said, “what will happen when we go to 1.2 GHz?” He has a few ideas. Schwalbe said the 1.2 GHz will shed more light on what goes on inside a cell, such as how they build proteins or ribonucleic acid (RNA). In the latter process, cells add about 20 new nucleotides to the molecule per second. Due to limited field strength,
At 1.5 GHz (35.2 teslas), the Series Connected Hybrid (SCH) has a field strength even higher than the coming 1.2 GHz machines. But because it is a hybrid, its field is less uniform than the all-superconducting 1.2 GHz instruments. Still, the field’s uniformity is better than in physics magnets, and very effective for looking at solid biological samples, which don’t demand as stable a field as solution samples. Since coming online this year, the SCH has generated impressive data that buttress the case for more strong NMR machines, said Bill Brey, a National MagLab physicist overseeing instrument development for the SCH. Because of its very high field, the SCH can detect atoms that, until now, have been invisible to NMR, notably oxygen. The ability to observe oxygen in molecules is a game-changing capability that will allow scientists to watch the body in action at the molecular level. “Oxygen has a number of interesting things about it,” Brey said. “It’s real biochemistry, not just structure — right in the active places on the molecule.” Oxygen, neurons, drug targets, weird electron behaviors: just a few of the mysteries atop scientists’ most wanted list. With the higher fields promised in next-generation magnets, researchers say, more dreamed-of discoveries will land squarely in their crosshairs.
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Several materials are in the running to build the next generation of superconducting magnets. Which will emerge the victor? here’s nothing like a good, old-fashioned race to heat things up. And that’s exactly what’s happening across the world as engineers and scientists crunch data, test materials and assemble prototypes. Their goal: Find the best way to turn high-temperature superconductors (HTS) into world-record magnets. To enable new science (see the accompanying story, Fields of Dreams on p. 14), teams in the U.S., Asia and Europe are developing HTS technologies for research magnets, particle physics and other applications. At CERN, for example, planning is underway to build a larger Large Hadron Collider that would be almost four times as long as the existing collider and require thousands of superconducting magnets. HTS materials can also 18
be used to build magnets for X-ray and neutron scattering experiments and even to study dark matter. In the U.S., a race within a race began this year at the National High Magnetic Field Laboratory, where leaders are convinced HTS materials will boost magnets to the next level. What they aren’t sure about yet is which HTS basket to put their eggs into. Luckily, the lab houses a diverse group of HTS experts. So, funded by a $4.2 million grant from the National Science Foundation, they have formed four teams, each tasked with developing, in parallel, a different HTS design. In the end, one will be chosen to wind coils for a planned
40-tesla magnet that would pave the way for the next generation of high-field hybrid and superconducting magnets. These new instruments could help revolutionize the fields of particle physics, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). The HTS super-contenders include two made from bismuth strontium calcium copper oxide, or BSSCO, and two from rare-earth barium copper oxide, or REBCO. Why the four-flanked attack? “No one conductor is the perfect package,” explained Lance Cooley, director of the National MagLab’s Applied Superconductivity Center (ASC). The question is, which will check the most boxes in terms of cost, safety, reliability, material strength, field quality, resilience and ease of use? One thing is certain: A long, twisting and potholed path lies ahead.
HIGH AND MIGHTY Scientists have been studying stuff inside electromagnets for more than a century. So why do they need new materials to make them? The building blocks they’ve used until now are copper alloys for resistive magnets and niobiumtin (NbSn) and niobium-titanium (NbTi) for low-temperature superconducting magnets. Both approaches face limitations preventing them from reaching fields much higher than they do today (about 41 teslas for resistive magnets and 24 teslas for low-temperature superconducting magnets). Those fields wouldn’t even make HTS break a sweat — at least theoretically. Discovered three decades ago, high-temperature superconductors, as their name suggests, can operate at less frigid temperatures than their low-temp cousins. More to the point for magnet makers, they can also keep working well beyond 24 teslas. Some may operate upward of 50 teslas, according to David Larbalestier, chief materials scientist at the National MagLab, and have the potential to smash a huge magnetic field barrier that has been holding scientists back.
As the next step to realizing those ultra-high fields, engineers at the MagLab must first finish their HTS homework. “No magnet is ever better than its conductors,” cautioned Larbalestier. “You better understand those conductors, their defects and how they operate under the very intense stress and energy density conditions of an ultra-high-field magnet.” Which brings us back to our race: Ready, set — and they’re off!
A SLEEK FRONTRUNNER And already the slim, trim, “no-insulation” (NI) REBCO has bounded into the lead. This fleet-footed frontrunner already has a major coup to its credit: In 2017, it broke the world record for an HTS coil operating inside a resistive magnet. Its 14.3-tesla field, combined with a resistive field of 31.2 teslas, generated 45.5 teslas. Traditionally, magnet makers weave insulators between the conducting turns to direct the current efficiently. But the clever NI design jettisons the insulation as a strategy to protect the magnet from a quench. Quenches are to magnets what collisions are to motorists: Nobody likes them, and they may never
You look at no-insulation and you think, ‘Yeah, that’s really cool — if you could pull it off.’
BC E R I
Photo: Stephen Bilenky
Photo: Stephen Bilenky
happen, but you had better engineer for one, just in case. Both quenches and car wrecks happen when a lot of energy is forced to come to a sudden, unexpected stop. Quenches occur when, perhaps due to a tiny imperfection, a conductor warms up enough to lose its superconducting property and reverts to normal electricity. The result isn’t as dramatic as a car crash. But when the electricity changes, so does the magnetic field, which has been storing a lot of energy. Without the right safeguards, all that energy will dump into that one failed section of the HTS coil, damaging, or even ruining, the whole thing. You can’t guarantee against quenches, but you can control them. Conventional, insulated superconducting magnets do this with built-in heaters and copper that acts as a kind of back-up system for current. As soon as a quench starts somewhere in the coil, the heaters rapidly warm up the rest of it so that the whole thing stops superconducting. Then the copper picks up the current until the magnet is ramped down, protecting the coil from serious damage. It’s a lot of trouble to go to, but absolutely necessary — if the magnet is insulated. But if there’s no insulation constricting the current to a specific path, it will just reroute itself to avoid the trouble spot and keep on superconducting. Because you don’t need all that copper as a backup system, you end up with a smaller magnet that experiences less mechanical stress and requires less reinforcing material. The result is a compact coil that more than doubles the magnetic field–generating power of the previous record and a current density that outperforms the other HTS materials in this race. “Superconductors are expensive,” said Cooley, “so the more current density you can get, the less conductor you need to make the magnet you want.” Unfortunately, “no insulation” does not mean “no aggravation.” Because current travels anywhere it wants around an NI coil, it is harder to predict the mechanical forces it will generate, and it’s harder for scientists running experiments to fine-tune the magnet’s field.
In the accelerator magnet community, it’s absolutely a game changer.
All in all, it’s a promising technology: Even engineers backing other candidates have to admit NI REBCO has a lot going for it. “You look at no-insulation and you think, ‘Yeah, that’s really cool — if you could pull it off,’” said Scott Marshall, lead engineer from a competing HTS group.
TAKING THE HEAT — AND THE PRESSURE Supporters of rival bismuth-2212 (one of the two candidates from the BSSCO family) hope they will be the ones pulling it off. And, boy, the pressure’s on! Luckily, Bi-2212 can take it — up to 1,500 pounds per square inch of it — and some high heat, to boot. In fact, in order to work, these coils require that brutal treatment (called overpressure processing) to activate their superconducting properties. Clearly, Bi-2212 is one tough contender, and promising for the type of magnets used in particle accelerators. “In the accelerator magnet community, it’s absolutely a game changer,” said Cooley, who is working with Lawrence Berkeley National Laboratory to develop this technology. “It’s a round wire, so you make a cable. Once you make a cable, you have the ability to use high currents.”
The operative word there: “round.” Round conductors are actually not the norm in the realm of HTS. For various reasons, neither REBCO nor Bi-2223 (the second bismuth-based compound in this race) are shaped into a round wire, though engineers would if they could and may one day get there. But for now, they’re manufactured as tapes, tricky for winding magnet coils because they’re anisotropic: They behave differently in a magnetic field depending on the orientation. So, extra points to Bi-2212 for its roundness. Throw in a few more because it stops superconducting at a lower temperature than the other materials in this race, which could make quenches easier to manage. Fabrication, though, is tricky: You can modify the coil before it goes in the furnace. But once it’s cooked, it’s cooked; if it didn’t bake just right, it’s too late to fix it. Luckily, MagLab experts continue to fine-tune overpressure processing, keeping Bi-2212 solidly in the running.
REBCO RIVALRY But nipping at its heels is insulated REBCO — NI-REBCO’s stockier big brother.
We have done far more than all of the other technologies combined. So there’s a big experience advantage.
Like many big brothers, REBCO has something it lords over its scrawnier sibling: It has already matured into a full-fledged magnet that will be available to scientists in 2019. Built with a combination of insulated REBCO coils and low-temperature superconductor (LTS) coils, the National MagLab’s 32-tesla superconducting magnet racked up a remarkable world record in 2017 with a field a third stronger than any previous superconducting magnet. And it was no proof-ofconcept prototype, like its younger, no-insulation sibling: It is designed and built for scientists to use. “We have done far more than all of the other technologies combined,” said Huub Weijers, project manager for the 32-tesla magnet. “So there’s a big experience advantage.” A decade in the making, the 32-tesla magnet has already provided scientists a wealth of data about insulated REBCO design. They have worked through lots of problems, like how to best join lengths of REBCO tape. Amazingly, each 50- to 100-meter-long section represents a single crystal, and engineers must carefully connect them to keep the current flowing smoothly. But engineers face an even bigger hurdle in scaling the design up to the 40-tesla range: protecting the magnet from quenching. If the LTS coil were to quench, it would damage the adjacent HTS coil by straining the material. The 32-tesla is designed to prevent that scenario by inducing a controlled quench in the HTS coil using a large battery bank to heat up the coil. But scaling that strategy up to a 40-tesla magnet would require an impractically huge battery bank. Weijers thinks there’s another way to tackle that problem: re-engineer the REBCO tape. The existing version, he said, is actually too good, with a current density far exceeding requirements. “It’s like having a jet engine on a crop duster,” Weijers said.
Limiting that current will reduce the amount of energy required to manage potential quenches, he said, keeping insulated REBCO in the running.
Photo: Stephen Bilenky
Photo: W. Scott Marshall
DON’T DISCOUNT THE UNDERDOG Last but not least, bringing up the rear of this fab field of four, is Bi-2223. Some consider the compound a long shot for 40-T material because of its lowest-in-class current density. So you’d have to use more of the stuff, resulting in a bulkier, costlier instrument.
“It might not be in the range of fields that we’re interested in getting,” said ASC Director Cooley. “Thirty teslas, maybe.” Still, the material has advanced to the finals for a reason: Manufacturer Sumitomo Electric has upped the product’s current density and improved its strength with a layer of nickel alloy. Plus, the magnet would be relatively easy to build: Buy the tape and wind the coils — no need for fancy cooking or trailblazing design. And by virtue of the conductor’s filamentary tape structure, it produces (like its bismuth brother, 2212) a field that is precise, controllable and predictable. In fact, several NMR magnets have already been built with 2223. And the price, at least for now, is right. Commercially available for more than two decades, Bi-2223 goes for $30 a meter — half as much as REBCO. It’s definitely too soon to count this underdog out, said engineer Marshall, head of Team 2223. “It could be that this stuff, which is the most mature conductor technology and tried and true, might actually turn out to be the most reliable magnet we can build,” he said.
AND THE WINNER WILL BE … Drumroll please: You! Me! All of us! That’s how the scientific process works. Research, fabricate, test, measure, repeat: The data will determine the winner. In fact, argues MagLab scientist Hongyu Bai, manager for the 40-T project, in this race, there are no losers.
This stuff, which is the most mature conductor technology, might actually turn out to be the most reliable magnet we can build.
“Different technologies have different advantages,” Bai said. “If they are not selected for the 40-T, they could be a good choice for other applications.” For example, like solving the mystery of dark matter and dark energy, which hog up most of our universe. One theory says they’re made up of axions, hypothetical particles that high-field magnets could help detect. “We’re talking to the axion community about building magnets like that,” said Mark Bird, director of magnet science and technology at the National MagLab, “and they would require hightemperature superconductors.” Each of these conductors will find its niche, whether that’s solving cosmological puzzles, transmitting electricity over long distances, powering particle accelerators or generating high-resolution MRI images. However this particular race shakes out, it will be a very big win for science. Science advisor: Huub Weijers.
Find links to more details on these four HTS candidates at fieldsmagazine.org.
DOUBLE FEATURE Researchers combine high magnetic fields and neutrons to learn more about superconductivity. Sometimes you need two tools to get the job done. Your doctor might need X-rays and an MRI to figure out what ails you. A woodworker might first use a band saw, then a radial saw. So, too, in science. Researchers often rely on a combo of instruments to attack a complex question. Here, we explain how researchers paired high magnetic fields (at the National MagLab) with neutron scattering (at the National Institute of Standards and Technology, or NIST, and Oak Ridge National Laboratory) to learn more about superconducting compounds made from iron. Got a Ph.D. in physics? Turn the page and dive right into an awesome infographic by NIST physicist Rob Dimeo that explains the research (“Spin excitations and the Fermi surface of superconducting FeS”). But if we lost you at “spin excitations,” the synopsis below will prep you for the nerdier take that follows. Scientists are interested in superconductors, which conduct current with perfect efficiency. Most work only at really cold temperatures.
But some work in relatively warmer environments (high-temperature superconductors, or HTS). Physicists are looking for one that superconducts at room temperature, a discovery that would be revolutionary.
So they are trying to understand at the atomic level how superconductivity works. Scientists believe different superconductors work in different ways. Iron-based superconductors such as iron selenide (FeSe) intrigue physicists for lots of reasons:
At super-low temperatures or high pressures, FeSe enters a phase called “nematic ordering,” when the spins of electrons tend to order in an “up/down, up/down” pattern. This behavior seems to be connected with FeSe’s transition to a superconductor. FeSe has properties conducive to superconductivity. Scientists deduced this by using high magnetic fields to draw its “Fermi surface,” a kind of energy map that shows how electrons can move through it. By bombarding FeSe with neutrons, scientists observed magnetic fluctuations of energy (those “spin excitations”) that they believe might be the “glue” that helps the electrons superconduct. To better understand FeSe, these scientists examined iron sulfide (FeS); both compounds superconduct and share a similar structure. They discovered that, unlike FeSe …
FeS showed no nematic ordering.
FeS exhibited different magnetic fluctuations of energy in neutron experiments. And its Fermi surface looks a lot different: Its electrons don’t influence one another much (i.e., they’re “weakly correlated”), in contrast to FeSe.
So FeSe is weird — in a good way. Its electrons are strongly correlated, like cars in a traffic jam: For one to move, they all need to all move. The electrons’ “effective mass” is relatively heavy because they all interact with each other, a behavior that has “HTS” written all over it.
But FeS is boring: It’s weakly correlated, has a relatively light effective mass and, although it does superconduct, it does so in a banal way (not HTS!). – by Kristen Coyne
ATTACK OF THE The alphabet soup favored by many scientists can make difficult concepts downright incomprehensible. by Kristin Roberts hey lurk in every corner of science — splattered across websites, sandwiched by parentheses within peer-reviewed publications, and supersized on signage. They are a barrage of random letters symbolizing complex scientific processes, programs or phenomena. ACRONYMS. Eeeeek! Acronyms (and their less cohesive cousin, initialisms) seem to be one of scientists’ favorite communication tools. But their use — or overuse — can torpedo the chances of readers actually comprehending what was written. Kipling Williams, a Purdue University professor of social psychology, describes how acronyms attack. “When we are unfamiliar with acronyms and abbreviations, we feel less intelligent, less connected to the topic and organization that is using them, feel less control over our situation, and less worthy of inclusion and attention,” Williams explained. But scientists see them as a critical time-saver. “Scientific terminology is complicated to say and write over and over again,” Lance Cooley, a researcher at the National MagLab, says. Cooley is the director of the MagLab’s Applied Superconductivity Center (usually referred to as simply “ASC”) and in that department, acronyms like HTS (high-temperature superconductivity), EXAFS (Extended X-ray Absorption Fine Structure) and FCC (no, not the Federal Communications Commission, but rather the Future Circular Collider) abound. “Scientists have learned to economize,” jokes Cooley. 26
Williams identifies three overarching reasons why people use abbreviations and admits that their use can be a double-edged sword. “For full members, acronyms are a way to feel included and special, like they have their own special language,” Williams admits. “It’s like a private club in which you are a member.” With applications across so many scientific disciplines, high magnetic field researchers have developed their own fair share of these shortcuts. From the aquatic-sounding SQUID (Superconducting Quantum Interference Device) and EELS (Electron Energy Loss Spectroscopy) to the downright DRAMA (Dipolar Recovery at the Magic Angle) of ALCHEMI (Atom Location by Channeling Enhanced Microanalysis), these acronyms can leave your head spinning. Some organizations are tripped up by their own names! “Even our employees often mix up the order of the letters for the High Field Magnet Laboratory (HFML) in the Netherlands and the National High Magnetic Field Laboratory (NHMFL),” shares Eric Palm, deputy director of the latter. So with acronyms skulking on every page, what’s a science reader to do? Williams suggests simply asking people to define their abbreviations and acronyms upon first usage or avoid using them altogether. “But asking can indicate to others that you are not knowledgeable about something and are outside of the in-group,” he warns. “So it can be scary to ask.”
Test your acronym acumen Certain acronyms may be on your radar (an acronym for radio detection and ranging, by the way), but others may not. Test your acronym acumen by trying to complete the acronyms below. Then use those words to complete the secret message!
MAS: magic angle TPPI: phase increments
SQL: standard quantum
Exchange Experimental Fiber Field Frequency
Heat High Length Limit Performance
Secret Message Readersâ€™ heads are
SRF: superconducting radio
Strength Susceptibility Temperature Time X-ray
APPI: atmospheric photoionization
UTS: Ultimate tensile
pressure scientists to exchange them for high-performance words with strength!
Solution: Readers heads are spinning! Time to limit the frequency of acronyms and
Polarization Pressure Pulse Spectroscopy Spinning
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Learn why researchers need higher magnetic fields, what clues the Congo River contains about carbon cycling, and what’s behind EXAFS, ALCHE...
Published on Oct 5, 2018
Learn why researchers need higher magnetic fields, what clues the Congo River contains about carbon cycling, and what’s behind EXAFS, ALCHE...