A.C. Loss and Twisting Effect in Superconducting Composite Conductor

An electro-magnetic coupling effect in the twisted composite is studied experimentally. A change in the magnetic field dependence of the loss caused by the size of a superconductor and the frequency dependence of the A.C. loss are used to analyze the A.C. loss in relation to the twist-pitch. Samples studied are fine multi-core superconducting composites with Cu matrix containing 37 superconducting Nb-Ti-Zr filaments 23 µm in diameter. They are twisted at pitches of 2, 5, 20, 50 mm and infinity. The composite twisted at a pitch of 2 mm has no electro-magnetic coupling between superconducting filaments and the A.C. loss is equal to the sum of hysteresis losses of the filaments and the eddy current loss in a Cu matrix. The other composites have a coupling effect and the filaments behave as if they were one body. The twist-pitch dependence of the A.C. loss has a maximum.