Experimental study of loss mechanisms of AgAu/PbBi-2223 tapes with twisted filaments under perpendicular AC magnetic fields at power frequencies

AC Loss Reduction in Bi2223 Tapes with Interfilamentary Oxide Barriers

“…For the AC losses generated in the composite superconducting wire with normal metal matrix, it is widely known that the per-cycle coupling current loss component Q c generated in the matrix part show the maximum at coupling frequency f c , which is related to the decay time constant of coupling current τ c with following equation [3][4][5][6]:…”

“…For typical Bi2223 tape, n in a perpendicular field is approximately equal to the aspect ratio of filamentary region [3]. Although Q c decreases with increasing the frequency when the operating frequency f op of a tape is higher than f c , the superconducting filaments start to couple each other and the hysteresis loss Q h becomes considerably larger than completely decoupled case, at the condition of field amplitude B 0 above the full penetration field B p [12].…”

“…Although Q c decreases with increasing the frequency when the operating frequency f op of a tape is higher than f c , the superconducting filaments start to couple each other and the hysteresis loss Q h becomes considerably larger than completely decoupled case, at the condition of field amplitude B 0 above the full penetration field B p [12]. To achieve a significant loss reduction by decoupling the filaments, therefore, the f c value should at least be higher than the operating frequency f op [3][4][5][6][8][9][10]. Fig.2 shows the frequency dependence of AC losses per-cycle Q m in a perpendicular field at 77 K for SrZrO 3 + Bi2212 barrier tapes with different L t .…”

“…Although the critical current (I c ) above 150 A and the length of km-class are enough for the prototype configuration such as cables and transformers [1], their AC losses are still too large for the practical applications. The large loss generation in an AC external magnetic field is mainly attributed to strong electromagnetic coupling among the filaments [1][2][3]. The interfilamentary coupling is caused by the low resistivity of Ag-matrix and physical connection between the filaments by bridging.…”

“…The interfilamentary coupling is caused by the low resistivity of Ag-matrix and physical connection between the filaments by bridging. Moreover, because of the large aspect ratio of the tape geometry, both the hysteresis loss (Q h ) in superconductor and coupling current loss (Q c ) in a perpendicular field becomes much higher than in a parallel field and the conditions for filament decoupling becomes more restrictive [2][3]. To suppress the interfilamentary coupling and also to reduce the losses of Bi2223 tapes in a perpendicular field, therefore, not only twisting the superconducting filaments but also increasing the matrix resistivity is indispensable [3].…”