A conduction-cooled MRI model magnets wound with REBCO-coated conductors has been developed. Our final goal is to build the technology that makes 9.4 T MRI magnets for whole-body and brain imaging. Prevention of thermal runaway is one of the most important issue so that we have been developing a quench protection method using electrically conductive epoxy resin attached on the edge of the windings [1]. Because excessive current can bypass across turns in the radial direction, local heat generation is suppressed automatically. For scale-up with this method and verification with higher stored energy, the REBCO magnet constructed in this study has a REBCO multi coil composed of 100 single pancakes with an inner diameter of 500 mm and each one of them equipped with electrically conductive epoxy resin. The total conductor length was 31 km, and the total inductance was 91 H. The size of the homogeneous magnetic field region is 200 mm diameter spherical volume (DSV), in which the designed magnetic field is 3 T at 145 A, and the stored energy is 1 MJ. This presentation reports on the design, fabrication of 100 single pancakes and the multi coil, construction of the magnet, and test results in a conduction-cooled configuration. The coil was cooled to 10 K over 11 days and then the coil temperature was adjusted to 30 K. The operating current was gradually increased, and a central magnetic field was reached up to 3 T stably. After a series of charging tests, a quench protection test was performed by heating the 2nd stage of the cooling system while supplying 145 A to the coil. Although the coil temperature of the end unit rose to about 77 K, thermal runaway was prevented successfully and the coil was safely protected.

[1] H. Miyazaki, S. Iwai, et al: “Study on a Stacked REBCO Coil Composed of Six Single Pancakes with Electrically Conductive Epoxy Resin,” IEEE Trans Appl. Supercond., vol. 30, no. 4, Jun. 2020, Art. no. 4704105.

Keywords: REBCO, MRI, quench, protection