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Materials and Cost Benchmarking

First-Ever Fully Superconductive Coil Reaches Magnetic Field of 25 Tesla

12 June 2016

Conductors that are composed of materials that permit lossless and dense electrical currents at very low temperatures, even in high magnetic fields, are ideal for winding coils to generate very high magnetic fields. This is an important factor in applications like magnetic medical imaging, magnetic resonance spectroscopy for the analysis of complex molecules and even accelerator magnets.

Physicists at the University of Geneva (UNIGE) and the research and development team of Bruker BioSpin in Fällanden, both in Switzerland, wanted to generate ever-higher magnetic fields, so they started a collaboration in 2012.

Now they have finally developed and tested the first superconducting coil able to reach a magnetic field of 25 Tesla, which marks a first in Europe.

Details of the innovative superconducting coil, conceived and manufactured by researchers from UNIGE and Bruker BioSpin. (Image Credit: L. Windels/ UNIGE) Details of the innovative superconducting coil, conceived and manufactured by researchers from UNIGE and Bruker BioSpin. (Image Credit: L. Windels/ UNIGE)

The magnets used in nuclear magnetic resonance (NMR) and medical magnetic resonance imaging (MRI) today represent the primary commercial applications of superconductivity. NMR, used mainly in the chemical and pharmaceutical industry, allows for the discovery of new molecules, study of protein structure, or analysis of food content. These technologies are essential for drug development or the quality control of chemical compounds.

Modern measurement instruments available on the market today and the ones manufactured by Bruker BioSpin, in particular (a world leader in this field), can produce magnetic fields of up to 23.5 Tesla.

This limit is related to the physical properties of conventional superconducting materials used to generate the magnetic field.

"However, there is a need for more powerful spectrometers in the biomedical field,” said Carmine Senatore, professor in the Department of Quantum Matter Physics in the Faculty of Science at UNIGE. "Indeed, the stronger the magnetic field, the better the resolution of molecular structures. The goal of our collaboration was, therefore, to reach the new record for the magnetic field intensity of 25 Tesla with newly available superconducting materials, which was a real scientific and technological challenge. It is also an important milestone in the introduction of crucial technologies for the development of commercial ultra-high-field NMR products."

How They Did It

To create the magnetic field of 25 Tesla, the researchers combined a Bruker laboratory magnet, which produces 21 Tesla with an innovative superconducting insert coil, which increased the field by an additional 4 Tesla. In total, a field well beyond the 23.5 Tesla reachable with conventional superconducting coils could be generated.

To operate, the coil must be cooled with liquid helium to a temperature of –452.11°F. The superconductor chosen to achieve such a field was a copper-oxide-based ceramic, YBCO. A one-micrometer-thick layer of superconductor covered a thin steel tape, which was then wound onto a cylindrical support to obtain the coil.

To produce the superconducting insert coil, the team needed to use 140 meters of 3-mm wide tape.

In the preliminary design phase, the team studied and tested a variety of commercially available superconducting tapes in order to understand and control their electrical, magnetic, mechanical and thermal properties. They were faced with the challenge of finding a conductor with the right balance of properties—one that must carry high currents without dissipation, endure the winding process without degradation and withstand the magnetically generated mechanical stresses.

These properties were all successfully achieved.

"In addition to the achievable higher resolution, which will certainly stimulate the scientific community and the network of institutions working at the forefront of molecular science, the use of YBCO will also simplify the operation of NMR spectrometers by using less complicated cooling systems,” said Riccardo Tediosi, manager of Bruker BioSpin's Superconducting Technologies group.

This first 25 Tesla coil will act as an important part of the laboratory of applied superconductivity at UNIGE.

At this time, the coil is not a commercial product, but the fact that the researchers now know how to develop it will contribute greatly to commercial NMR systems.

In the near future, this record magnet will be used for basic and fundamental research while scientists and engineers will aim to achieve more challenging goals, such as an all-superconducting coil that generates stable and homogeneous magnetic fields beyond 30 Tesla.

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