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

Abstract

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.

Numerical Computation of AC Losses and Flux Profiles in High-Aspect-Ratio Superconducting Strips in Perpendicular AC Magnetic Field

“…They also say that for a large value of μ r , the calculated effects saturate. Claassen [26] has used a constant value of μ r = 100. The permeability of weakly ferromagnetic substrates has been measured [23], which has a parabolic dependence on the magnetic field, giving a maximum value of μ r = 200 at B a = 100 mT.…”

“…Fig. 6(a) also presents the ac loss in weakly ferromagnetic substrates [curve (e)] computed from the empirical relation of Claassen [26] Q Ni−W = 0.8 B 0.01 1.87 .…”

Magnetic field distributions around superconducting strips on ferromagnetic substrates

“…2,3 The magnetic behavior of ferromagnetic substrates can strongly affect the electromagnetic response of superconducting coated conductors. Although the effects of ferromagnetic substrates on ac losses of superconducting coated conductors have been extensively investigated experimentally and numerically, [4][5][6][7][8][9][10][11][12][13] ac losses in superconducting strips on ferromagnetic substrates have not been investigated analytically. Genenko et al 14 analytically investigated the magnetic field and current distributions in superconducting strips surrounded by soft magnets, but they did not consider realistic geometries similar to those of coated conductors.…”

Finite-element simulations of overcritical states of a magnetically shielded superconductor strip

“…For magnetically shielded strips, such overcritical states have been predicted analytically, though only in the idealized case of shields of infinite lateral extent and infinite magnetic permeability to date. Nevertheless, substantial redistributions of the transport current due to the presence of geometrically restricted shields of finite magnetic permeability have been established in numerical studies [10][11][12][13][14] and magneto-optical experiments [13,[15][16][17][18]. Recently, the enhancement effect of open, shielding softmagnet configurations on the critical current of superconductor strips has been confirmed in transport measurements and finiteelement simulations of full critical states for critical currents depending on the local magnetic field [19][20][21][22].…”