Influence of DC external magnetic field on AC transport current loss of HTS tape

We measured the AC transport current loss of Bi 2223 multifilament Ag-sheat hed tape under DC external magnetic field of 0-0.2 T. There were discrepanc ies between the measured data and Norris' formula for elliptical model in t he range of low value of I-p/I-c (I-p and I-c are peak of the AC transport current and critical current of the tape respectively), while without DC ba ckground field, the loss of the tape was close to Nonis' formula. Theoretic ally speaking, even with the DC background field and decreased critical cur rent the AC transport current loss of the tape follows Norris' formula whic h is derived from the Bean model. When DC background field is applied to th e HTS tape, n value of the power law E-J characteristics decreases together with the decrease of J(c). Dependence of the AC transport current loss on the n value was analyzed by numerical calculation. The results show that th e loss depends on the n value and that decrease of the n value is one of th e causes of the discrepancies between the measured data and Nonis' formula. (C) 1998 Elsevier Science B.V. All rights reserved.