Research engineer Dongkeun Park watches a thin, coppery tape of high-temperature superconductor (HTS) wind its way from one spool on his plywood worktable to another, cautiously overseeing the speed and tension of the tape’s journey.
When completed, in about half a day, this HTS double-pancake (DP) winding will look like two flat coils, one atop the other, but they will be one, connected internally, leaving both terminal ends on the outside. Park has been managing this process on and off for eight years, knowing that every turn of the coil creates a stronger magnet. This is just one of 96 double pancake coils that have been wound over the past five years for an 800 MHz HTS insert coil, the H800, being built in the Francis Bitter Magnet Laboratory (FBML) at MIT’s Plasma Science and Fusion Center.
High-field superconducting magnets are vital for nuclear magnetic resonance (NMR) spectroscopy, a technology that provides a unique insight into biological processes. The stronger the NMR magnet, the greater the detail and resolution in imaging the molecular structure of proteins, providing researchers with the information they may need to develop medications for combating disease.
Park joined the laboratory as a postdoc in 2009. He traces his interest in superconductivity, and MIT, to a lecture given by visiting FBML magnetic technology division head Yuki Iwasa at Yongsei University in Seoul, South Korea. Park says that as a graduate student in electrical engineering, “I wanted to make something by hand, not only by calculation.”
When Park first arrived at FBML, the lab had been working on high-resolution HTS-based NMR magnets since 1999 as part of a program sponsored by the National Institutes of Health (NIH) to complete a 1-GHz NMR magnet with a combination of low temperature superconductor (LTS) and HTS double-pancake insert coils. The lab’s work on LTS-based NMR began several decades earlier.
At the time of his arrival, NIH and MIT had recently agreed to increase the target strength of the magnet being developed from 1 GHz to 1.3 GHz. To reach this strength, FBML planned to create an H600 magnet and nest it inside a 700 MHz LTS (L700) magnet, which could be purchased elsewhere. Park notes that this combination translates to a magnetic field strength of 30.5 Tesla, “which would make it the world’s strongest magnet for NMR applications.”
One responsibility given to Park, along with his colleague research engineer Juan Bascuñán, was to wind each DP, then test it in liquid nitrogen. The DPs would then be stacked, compressed, joined together and retested as a finished coil. Finally, this stacked coil would be over-banded with layers of stainless steel tape to support the much larger electromagnetic forces generated during high-current operation in liquid helium. Park and his colleagues needed to create two of these coils, one slightly larger than the other, and nest them inside a series of LTS coils to create the final magnet. The combined coils would create a magnet that could provide the sharpest imaging yet for investigating protein structure, possibly three times the image resolution from FBML’s current 900-MHz NMR.
In December 2011, Park and his colleagues had virtually finished the preliminary DP windings, and were looking forward to stacking them for further testing. But returning from MIT’s winter recess, they discovered that the coils were missing. The 112 double pancake coils they had carefully crafted and wound for the H600 had been stolen.
Park’s current PSFC colleague, research scientist Phil Michael, suggests that the theft, though traumatic to the project, “ultimately made the magnet better.” To save money, MIT and NIH decided that instead of purchasing an L700 magnet to surround the H600 coils as originally planned, they could use an L500 coil already on hand at FBML, and create for it a higher strength HTS magnet: the H800.
With new security measures in place, Iwasa’s group set out to accomplish this goal by adopting a new HTS magnet technology known as no-insulation winding, developed by Park along with former FBML research engineer Seungyong Hahn. All previous coils had been created from HTS tape insulated with plastic film or high resistive metal. The new coils would be made without the insulation, allowing them to become more compact and mechanically robust, with increased current density.
Park did not take part in the early production of the H800. In February of 2012, he decided to pursue an opportunity to make a new commercial magnetic resonance imaging (MRI) magnet for Samsung Electronics in South Korea and the UK. In 2016 he happily returned to MIT as a research engineer, his hiatus having provided him an appreciation for the benefits of an academic environment.
“A company’s objective is to make a profit. So you must always be concerned with reducing costs,” he says. “This is very different from exploring basic science and engineering on innovative ideas at MIT.”
Although many coils for the H800 had been wound in his absence, he returned in time to complete and test more than half the required DP coils, along with team members Bascuñán, Phil Michael, Jiho Lee, Yoonhyuck Choi, and Yi Li. As 2018 approaches the three HTS coils necessary to create the H800 are nearly completed. Only Coil 3 remains to be finally tested in liquid helium. As the new year begins, the coils will be combined and tested as the H800.
But even after the H800 is nested in the L500 coils and the target 1.3 GHz magnet is created, there will still be three to four years of work to ready it for the high-resolution NMR spectroscopy that will provide new insights into biological structures. Until then, Park will remain patient as he looks to other projects he is overseeing, including one developing an MRI magnet for screening osteoporosis.
And yes, his new project requires superconducting coils. Park is always ready to start winding.