INDUCED CRITICAL-CURRENT DENSITY LIMIT OF AG SHEATHED BI-2223 TAPE CONDUCTOR

We have already reported the best critical current density of 66,000 A /cm2 with an Ag sheathed Bi-2223 tape conductor. The Brick-wall model is for explaining the current transport mechanism of this conductor. T he model has its roots in the fact that the Bi-2223 tape com is a comp licated stack of crystals which have a mica-flake structure. The orien tation of the crystals seriously affects the current transport capabil ity. Moreover, the contacts between the stacking crystals are very imp ortant. The transport current flows dividing into many branch paths. U nder high magnetic field, the different paths experienced different el ectromagnetic forces. Differences between the electromagnetic forces o n the different crystals can affect the contacts so as to increase res istivity and decrease overall critical current density of the tape. Th is effect can foretell the limit of the critical current density obtai nable with these kind of conductors.