Improvement of coil performance by optimal use of multifilamentary superconducting tapes

It was theoretically confirmed that improvement of superconducting-coil performance can be obtained by making optimum use of multifilamentary tapes with high aspect-ratio cross-sections. Superconducting tapes, such as NbTi and MgB₂ multifilamentary tapes, are known to have anisotropic electromagnetic properties, i.e., critical current densities and ac losses; under external transverse magnetic fields which are parallel to the tape face, the critical current density is higher than that of the multifilamentary round wire, but the ac loss is lower. For tapes with a high aspect-ratio cross-section, the anisotropic properties are still more remarkable, and therefore it is predicted that such a tape with superior electromagnetic properties will prove valuable as the windings of high performance coils for practical applications. In this paper, some examples of coil arrangements such as single or plural solenoid coil systems are shown in order to highlight the usefulness of this superior tape performance. The effect of the high aspect-ratio of tape cross-section on the electromagnetic coil performance was also discussed, taking the cooling condition of coil windings into account.