Self-field AC losses of assemblies of Ag sheathed PbBi2223 tapes

Magnetic interaction between two neighbouring superconducting tapes carrying a transport current can cause them to become coupled so that they react as one tape. One of the consequences of such coupling is the increase in the self-field loss per tape. The critical distance at which the tapes begin to couple is important in the assessment of the interactions among tapes in systems such as a power cable or coil. Experimental measurements of the self-field losses in two neighbouring Ag sheathed PbBi2223 tapes carrying the same transport current were carried out with the two tapes separated by various distances, while placed one on top of the other (stack-configuration). This configuration is similar to that found in adjacent layers in a coil. The results indicate that the critical coupling distance for the top-configuration is about 5 mm, where the increase in loss per tape is about 10%. Measurements are also undertaken for the more realistic situation where each of the tapes has a different critical current.