Determination of irreversibility field variations in mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox tapes by transport current methods

Abstract

The irreversibility field, H*, has been measured for a variety of mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes using two different transport current techniques. It is common to characterize the quality of 2223 tapes by their zero-field, 77 K critical current density [Jc(0 T, 77 K)], even though this ignores the fact that significant self-fields depress Jc(0 T, 77 K) and the possibility that the in-field Jc(B) characteristics may be optimized independently of the Jc(0 T, 77 K) value. To provide more useful information, we propose a second characterization, that of the irreversibility field, H*. Having both H* and Jc(0 T, 77 K) information helps in separating the two independent contributions that better connectivity and stronger flux pinning can make to the Jc of a tape. We illustrate this point with results from a variety of mono- and multifilamentary Bi-2223/Ag tapes in damaged and undamaged conditions, which show that H* (77 K) can vary from ∼100 to ∼200 mT and not directly correlate with Jc(0 T, 77 K). The two proposed protocols for H* measurement are robust and compatible with common transport measurement procedures.