Transport properties of Tl-Ba/Sr-Ca-Cu-O metal sheathed superconducting tapes in magnetic fields

Ag- or Au-sheathed taped with a Tl-Ba/Sr-Ca-Cu-O core were fabricated by a drawing-rolling and subsequent pressing method. The tape prepared at an optimized condition yielded a transport J_c of 15900 A/cm² at 77 K in the absence of a magnetic field, and 1100 A/cm² in a magnetic field of 1 T. The enhancement of J _c in a magnetic field was thought to be caused by an improved junction between grains and an unintentional introduction of a pinning center from various defects and unknown crystal phases. A 67-turn-pancake coil was made from a 10-m-long, 0.14-mm-thick and 2.5-mm-wide Ag-sheathed tape, which was capable of at least a 7-A critical current at 77 K in the absence of a magnetic field. The coil generated up to a maximum magnetic field of 103 G (a coil current of 3.0 A) without resistivity in liquid nitrogen