Calculations of Critical Current Densities for Type-II Superconductors (I)

In this paper, for mixed state in Type-II superconductors London equation is solved by using normal core model which gives boundary conditions in the same way as Coffey, to obtain the interaction force between a fluxoid and fluxoids lattice. This interaction force that is repulsive is considered pinning force as Coffey has proposed. As loss mechanism normal eddy-current damping and cycloid damping are considered and we get the expressions of viscous coefficient and induced voltage across superconductor, that are rather different from the ones given by Kim, et al. Our expression of voltage across the sample does not equal to ν_LB/c, which is usually adopted in flux flow theory, where ν_L is fluxoid velocity and B magnetic induction. Two forms of critical current density as a function of reduced external magnetic field for a given criterion voltage appeared in sample are found and plotted for various values of parameters. Also discussion is made about voltage induced by fluxoid motion in superconductor.

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