Improved stability of magnetic field in superconductor coils by applying twisted Bi-2223 multifilamentary tapes

李全, 雨宮尚之, 中村武恒（京大）

Abstract:One of main factors, which determine the magnetic field quality of NMR and MRI magnets, is the stability of magnetic field in high TC superconductor coils that is strongly affected by shielding current (screening current). In this paper, unconventionally, twisted Bi-2223 multifilamentary tapes are applied winding coils in order to reduce the magnetic field generated by shielding current that consequently improves their stability of magnetic field. Two coils, wound with 2.7 mm wide untwisted and twisted Bi-2223 multifilamentary tapes respectively, are prepared and measured at 77 K supplying current at selected values. Each coil consists 10 stacks of double pancake coils with 70/80 mm inner/outer diameter. It is testified that the magnetic field generated by shielding current can be effectively reduced by using twisted tape, and smaller amount of hysteresis can be achieved.