Current-Voltage Characteristics of Superconducting Foils in Small Oscillatory Magnetic Fields

Abstract

The current-voltage characteristics of a type II superconducting foil is calculated in terms of the generalized time-dependent Ginzburg-Landau equations in case of a superposed small ac magnetic field. The displacement of fluxoids inside the pinning potential is obtained by solving the force balance equation which is derived by minimizing the Helmholtz free energy. The result shows that the mechanism proposed by Derlieu which is based on the critical state model is not fully applicable for a high magnetic field near H_c2. Nondissipative component of a transport current density differs from the assumption made by Derlieu and is not always equal to the critical current density. This is due to the fact that the displacement of a fluxoid cannot attain its maximum value since the fluxoid lattice has a large shear modulus c₄₄ whereas an effective spring constant is very small in the vicinity of H_c2.