Calculation of decrease in A.C. losses in wires of type II superconductors in longitudinal magnetic fields

We present two models for calculations of A.C. losses in wires of type II superconductors in static axial fields. Both models exploit the critical state equation using F
p
= μ
o
α(T)B(1 - B/H
c2
). In cylindrical geometry this needs to be supplemented by an additional prescription. For one model, we assume pure axial current flow (jθ = 0). In the other, an empirical critical orientation equation dφ/dr = ± k F
p
\cos
²
φ/B
²
is introduced to govern the angle φ flux lines make with the z axis as they move in and out during the current cycle. The calculated curves are compared with existing data on A.C. losses at low frequencies.