STUDY OF THE SUPERCONDUCTING TRANSITION AT HIGH PULSED CURRENT OF BULK BI-2223 SINTERED AND TEXTURED BY HOT-FORGING

In this study, the transition of Bi1.8Pb0.4Sr2Ca2.2Cu3O10.3+x ceramics in the form of both textured and sintered bars is investigated at 77 K using high pulsed currents with a duration varying from 1.25 to 20 m s, Two types of behaviour are observed: (i) When the average temperatu re T of the sample is lower than T-c = 110 K, a critical current is re covered at the end of the pulse, probably because of good thermal exch ange between the sample surface and the bath and because the critical current density exists up to 110 K; (ii) above this temperature, the s ample remains normal after the pulse because the energy dissipated is too high. No deterioration in the sample is observed and experiments c an be reproducibly repeated. The maximum instantaneous power applied t o the material is 140 GW/m(3) and the maximum energy per unit volume t ransmitted to the sample after a 20 ms pulse is 925 MJ/m(3). V(I) curv es for sintered and textured samples are compared. At 15 times I-c, th e measured electric fields are 1000 V/m and 400 V/m for textured and s intered samples, respectively. Using specific heat data and assuming a diabatic heating, the average temperature reached after pulse is calcu lated. Resistivity curves are obtained for sintered and textured mater ials which are in good agreement with classical measurements on small samples. (C) 1997 Elsevier Science B.V.