Effect of substrate magnetism on the ac loss of high temperature superconductor tape-wound coils

Magnetism can affect losses in superconducting coils in two ways. First, there is magnetic loss ('core loss'). This can be separately measured as a function of magnetic induction in the material of interest (usually the substrate on which a superconducting film is grown). One can then find the fields in the coil when a current is applied and calculate the magnetic loss. A second mechanism, which has not been previously addressed, is an enhancement in the ac losses in the superconductor itself due to increases in the local magnetic fields. This contribution depends on the permeability of the magnetic material. Both contributions are calculated for a specific coil geometry using magnetic properties of a NiW alloy. In this example it is found that the latter contribution can be significantly larger than the former.