Abstract
The current-carrying ability of a type-II superconductor is generally represented by its critical current density. This can be determined by measuring a flux relaxation process starting with a testing current density that is greater than or equal to the critical value. Here we show that a flux relaxation process starting with an intermediate current density can be converted into a process starting with the critical current density by introducing a virtual time interval. Therefore, one may calculate the critical current density from the flux relaxation process starting with a current density below the critical value. The exact solutions of the time dependence of current density in the flux relaxation process were also discussed.
Highlights
Critical current density is the maximum current density that can be carried by a type-II superconductor
The flux relaxation phenomenon can be described by the Arrhenius equation in case of thermal activation. This suggests that a flux relaxation process has a strong dependence on temperature and vortex activation energy.[5]
If the flux relaxation process starts with the critical current density jc, the initial vortex activation energy Ui is zero, i.e., Ui | j= jc = 0
Summary
Critical current density is the maximum current density that can be carried by a type-II superconductor. One can determine the pinning potential from a flux relaxation process, which is the phenomenon that quantized vortices jump between adjacent pinning centers spontaneously due to various reasons.[1,2,3,4] The flux relaxation phenomenon can be described by the Arrhenius equation in case of thermal activation This suggests that a flux relaxation process has a strong dependence on temperature and vortex activation energy.[5] The vortex activation energy is a decreasing function of current density because it can be reduced by the Lorentz force of the current density. A number of current dependent vortex activation energies[6,7,8,9,10,11] were proposed on the basis of different physical considerations Using these vortex activation energies, one can obtain the corresponding time evolution equations of the current density.[5]. Let us derive the generalized expression for the time dependence of the vortex activation energy
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