Reduction of the ac losses of multifilament superconductors by the use of low twist rates

摘要

The ac losses of differently twisted samples of a multifilament superconductor in a magnetic field B=Bs +B0 sinωt have been measured. The over‐all loss per cycle has a maximum at a frequency fm, which shifts to smaller frequency values with decreasing twist rate. At certain frequencies a multifilament superconductor has lower over‐all losses when its twist rate is decreased. The reason is that the coupling current losses in the matrix decrease with increasing twist for f≪fm but increase with increasing twist rate for f≳fm.