Reduction of Screening Current-Induced Magnetic Field of REBCO Coils by the Use of Multi-Filamentary Tapes

The screening current-induced magnetic field (screening field) for REBCO tape coils is a critical problem for superconducting coil systems which require accurate magnetic fields, such as NMR, MRI and accelerators. The magnitude of the screening field depends on the width of a REBCO layer in a tape. Therefore, a fundamental method to reduce the screening field is to use multi-filamentary REBCO tapes. Experimental and simulated results demonstrate that the use of multi-filamentary REBCO tapes reduced the screening field and the effect is pronounced for medium to high load factor operation, due to full penetration of the magnetic field and the transport current effect. The multi-filamentary tapes also reduce the temporal drift of the magnetic field after the coil charge. If we use multi-filamentary REBCO tapes with a filament width of 0.6~0.9 mm, the screening field is reduced to the same level as Bi-2223 coils.