Electromagnetic interfilament coupling of silver-sheathed Bi-2223 multifilamentary tapes in transverse AC magnetic fields

To discuss the electromagnetic interfilament coupling of silver-sheathed multifilamentary Bi-2223 (HTS) tapes, AC losses of HTS tapes with various twist pitches and sample lengths in transverse magnetic fields were measured at 77 K by a magnetization method. Both hysteresis loss and eddy current loss in fields perpendicular to the HTS tape surface were approximately one order of magnitude greater than those in parallel fields. While AC losses in parallel fields were extremely reduced with a decrease in the twist pitch or the sample length, those in perpendicular fields scarcely decreased. AC losses of the untwisted HTS tape, which were proportional to the frequency in a perpendicular field of 29 mT, were slightly smaller below 70 Hz and larger above 150 Hz than those of the HTS tape twisted at a pitch of 8.6 mm. It is concluded that the coupling loss of untwisted HTS tapes is much smaller than the eddy current loss at commercial frequencies because of complete electromagnetic interfilament coupling.