The material currently used in magnetic resonance (MR) imaging machines in both hospitals and research laboratories -- a low-temperature superconducting alloy of the metallic element niobium -- has been pushed almost as far as it can go, to around 21 Tesla. (Tesla is used to define the intensity of the magnetic field.) There are no superconducting magnet wires currently available that can generate 30 Tesla.
"A new materials technology -- such as a technology based on high-temperature superconductivity -- is required to make the huge leap from 21 Tesla to 30 Tesla," said William P. Halperin, John Evans Professor of Physics and Astronomy in the Weinberg College of Arts and Sciences at Northwestern, who led the team. "We have shown that Bi-2212 could be operated at the same temperature as is presently the case for magnets made with niobium -- 4 degrees Kelvin -- and also achieve the stable state necessary for a 30 Tesla magnet."
The findings will be published online Feb. 11 by the journal Nature Physics.
"We are exploring nature's limitations, and our discovery has basic implications for the study of superconductors and for applications to magnetic resonance imaging," said Halperin. "The dream would be to have powerful magnets that don't require helium for cooling. Some day new materials might be discovered where this restriction is lifted, but it isn't possible at the present time."
A superconductor, when cooled to its appropriate temperature, conducts electricity without any resistance. Superconductivity first appears in Bi-2212 at a high temperature of 90 degrees Kelvin, but Halperin and his colleagues found that the stable state required in high-magnetic fields can be established only when the temperature falls below 12 degrees Kelvin. The team is the first to establish this limit for Bi-2212.
"Sometimes what seems to be bad can be good," said Bo Chen, lead author of the paper and a graduate student of Halperin's. "Our findings set a speed limit. If you go beyond this speed you may have trouble. Knowing the upper temperature limit is a kind of security."
"To create a 30 Tesla magnet, we need a superconducting material that can carry the required amount of electricity without blowing up," said Halperin. "We have found that the operating temperature for Bi-2212 must be below 12 degrees Kelvin. The good news is that this temperature can be reached by cooling the magnet with liquid helium. If we had found the upper limit to be 2 degrees Kelvin then the cryogenic requirements would be intractable."
MR imaging is widely used by hospitals for medical diagnosis, and scientists at universities, national laboratories and pharmaceutical companies use even more powerful MR technology to study DNA, proteins and other complex molecules. About a dozen labs around the country take advantage of the highest magnetic field now in use -- 21.1 Tesla, which produces a magnetic field 10 times larger than your average hospital machine. Increasing the field of the magnet even a small amount, from 21.1 to 22.2 Tesla, would increase the cost of the machine by two million dollars.
"A holy grail of the scientific community, as set out recently by the National Research Council, is to build a superconducting magnet of 30 Tesla," said Halperin. "In MR imaging, the higher the magnetic field, the higher the resolution, which provides scientists with more detail for analysis. A 30 Tesla magnet could drive significant advances in chemistry, biology and medicine."
Using MR techniques at the National High Magnetic Field Laboratory in Tallahassee, Fla., Halperin and his team studied Bi-2212, one of the "darlings" of superconductivity. To measure its properties, they put the rare isotope oxygen-17 into a crystal of Bi-2212, with the isotope acting as a probe, much like a fluorescent dye. They then determined the phase diagram of the material where superconductivity is stable, which showed high temperature and high magnetic field could not be achieved together.
"Now that we have this information about Bi-2212, the next question is, 'Can such a magnet actually be made?'" said Halperin. "I really don't know -- it depends on engineering and processing the materials to make them into wires. My fellow scientists and engineers will have to solve the materials problems, and they don't like to accept no as an answer."
Megan Fellman | EurekAlert!
NASA's Fermi catches gamma-ray flashes from tropical storms
25.04.2017 | NASA/Goddard Space Flight Center
DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
25.04.2017 | Physics and Astronomy
25.04.2017 | Materials Sciences
25.04.2017 | Life Sciences