TRANSPORT-PROPERTIES OF LONG MONOFILAMENTARY BI(2223) TAPES

Monofilamentary Bi(2223) tapes with J(c) (77 K, 0 tesla) up to 30 000 A/cm(2) have been prepared by cold rolling using the powder-in-tube method. An optimization of the precursor powders has led to a higher phase purity after the reaction heat treatment. The deformation process has been optimized in order to increase the oxide density and to reduce sausaging effects on the oxide thickness. The transport proper ties of these tapes have been studied in a wide range of temperatures (4.2 K-T-c) and magnetic fields (up to 28 tesla). The critical-current values at 77 K and fields of 0.5 T and 1 T parallel to the tape surface are 10 000 A/cm(2) and 5 400 A/cm(2), respectively. At 4.2 K the J(c) value decreases from 1.6 . 10(5) A/cm(2) at 0 T to 6 . 10(4) A/cm(2) at 15 T. At fields higher than 15 tesla a very low field dependence of J(c) has been found, regardless of the tape orientation. Transport properties have also been studied by cutting small sections of the tape in order to investigate the local critical-current distribution. It has been found that, even in rolled tapes of good quality ( J(c) (77 K, 0 T) > 20 000 A/cm(2)), the J(c) distribution is homogeneous: the critical current density increases gradually from the centre of the tape to the sides, the latter exhibiting much higher J(c) (46 000 A/cm(2)) than in the centre (18 000 A/cm(2)).