Time Constants of Flat Superconducting Cables

Abstract

The frequency dependence of coupling losses is calculated for flat superconducting cables, including the electromagnetic coupling between different current loops on the cable. It is shown that there are two characteristic time constants for both parallel and transverse coupling losses. The values of these time constants τ ₀ and τ ₁ are calculated by introducing effective inductances for the current loops. In both cases, τ ₁ is considerably smaller than τ ₀. As the most important methods of determining τ ₀ from AC losses — namely, the limiting slope of loss/cycle at zero frequency and the position of the maximum loss/cycle vs. frequency — estimate τ ₀ and τ ₁, respectively, the results are important for practical measurements and evaluation of tune constants from AC losses. At larger frequencies, the losses are more likely to those in normal conductors (skin effect). The calculation schemes can be applied to cables with closely wound strands (like the cable-in-conduit conductors), too. However, several other effects should be considered being different and/or more important with respect to other cable types (demagnetization factor of strands and cables, larger regions near the cable edges, smaller number of strands and subcables, etc.).