Built with both traditional and novel superconducting materials, the magnet reached a field of 27 teslas on June 5 in a test that exceeded designers’ expectations. The magnet is a smaller version of an even more powerful magnet due for completion next year — a 32 tesla all-superconducting magnet that will be substantially stronger than any such magnet built to date.
Tesla (“T” for short) is a measure of magnetic field strength: A typical magnet used in an MRI machine is 2 to 3 Tesla. The 27 Tesla field reached last week was 3.5 Tesla stronger than the strongest superconducting magnet currently in operation (in Lyon, France) and 1 Tesla stronger than a superconducting test magnet built earlier this year in South Korea. For decades, engineering and materials advances have nudged the record up only bit by bit. Last week’s feat brings MagLab engineers to the home stretch of the seven-year 32 T project.
This YBCO test coil helped the MagLab set a new world record for superconducting magnets: 27 teslas.
YBCO tape (running the length of the table above) was wound into discs called “pancakes” to make the insert coils. A model “pancake” made from copper is pictured above.
The strongest superconducting user magnet in the world currently has a field strength of 23.5 tesla. When this ambitious project is completed in 2016, the strongest superconducting magnet on the planet will be housed at the MagLab. At 32 tesla, it will be a whopping 8.5 tesla stronger than the current record – a giant leap in a technology that, since the 1960s, has seen only baby steps of 0.5 to 1 tesla. In June 2015, a test for the 32 tesla magnet set a new world record of 27 teslas for an all-superconducting magnet.
The groundbreaking instrument will considerably reduce the cost of scientific experiments and make high-field research accessible to more scientists. The system will also support decades worth of new science. Due in large part to the quieter environment a superconducting magnet offers over a resistive magnet of equivalent strength, the 32 tesla will help scientists break new ground in nuclear magnetic resonance, electron magnetic resonance, molecular solids, quantum oscillation studies of complex metals, fractional quantum Hall effect and other areas.
Short for yttrium barium copper oxide, YBCO is a high-temperature superconductor (HTS) that was fashioned into a tape-like form by SuperPower Inc. of Schenectady, NY, in collaboration with the MagLab. HTS superconductors are superconducting at higher temperatures than their LTS cousins — a big plus. That property also allows them to remain superconducting to much higher magnetic fields than LTS materials.
The magnet tested last week features a mix of YBCO tape and LTS wire, as will the finished 32 T. SuperPower president Yusei Shirasaka shared the excitement over the achievement and his company’s partnership with the MagLab.
“Our relationship with the MagLab has allowed us to grow and learn, with the constant drive to perfect our products,” Shirasaka said. “SuperPower’s recent advances in pinning structure, thinner substrates and other improvements will form the basis for the MagLab’s next generation of magnets.”
Another partner on the 32 T project was Oxford Instruments, which constructed the LTS coils. The HTS coils and other key technologies were developed and constructed at the MagLab. The prototype that integrates the LTS and HTS coils performed beautifully in its tests, reported MagLab engineer Huub Weijers. As director of the 32 T project, Weijers has tested a number of magnet coils over the years.
“This is the first time with the prototypes that we’ve not had something that wasn’t quite right,” Weijers said of last week’s test. “Every time, there was a piece here or a part there that wasn’t quite right, that was limiting us overall. This time there was no such irregularity. We just reached the maximum performance of the conductor, which is ideally where you’d like to get.”
The MagLab boasts several instruments that are stronger than 32 T, including two resistive magnets and the world-record 45 T hybrid magnet. However, as the world’s strongest superconducting, the 32 T will be able to run longer hours, be cheaper to operate, and offer important advantages for some types of experiments. Superconductors create steadier, “quieter” fields than resistive magnets (which depend on conventional current) that are important for experiments in nuclear magnetic resonance, electron magnetic resonance and other areas of research that require more sensitive measurements.
The successful test gives Weijers and his team new momentum as they approach the final phases of the project. The completed 32 T magnet is projected to be ready for scientists in the first half of 2016.
The 32 tesla will be the first high-field magnet available to researchers to incorporate YBCO, a finicky material a few commercial companies have been developing for years in collaboration with MagLab engineers and scientists. The finished, 2.3-ton magnet system will feature about 6 miles of YBCO tape, formed into 112 disc-shaped “pancakes.” Two inner coils of YBCO, fabricated at the MagLab will be surrounded by a commercial outsert consisting of three coils of niobium-tin and two coils of niobium-titanium.
The new magnet will particularly be more attractive for users whose experiments require lower noise and longer running times than the resistive magnets can offer, while the relatively fast ramp-rate of 32 T/hour in this superconducting magnet also allow for many field sweeps per day.
The so-called “outsert” magnet system from Oxford Instruments generates 15 T within a very large magnet bore of 250 mm, operating at 4.2 Kelvin. The additional 12 T came from high temperature superconducting (HTS) coils developed by the National MagLab. The 27 T result is a significant milestone on the way to the National MagLab’s goal of a 32 T all-superconducting magnet.
The prototype HTS coils developed by National MagLab use 4 mm YBCO tape from SuperPower Inc. (Schenectady, NY) and were operated to 265 A in the full Oxford Instruments 15 T outsert magnet, for the combined magnet central field of 27 T at 4.2 K, the normal boiling point of liquid helium
SOURCES – National Maglab, Oxford Instruments
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