Effect of viscous forces in type II superconductors under A.C. conditions

Viscous forces on flyxons under a.c. conditions are shown to be most important in the region in the superconductor where the flux density is zero between regions of fluxons of opposite sign. The results of this effect should be observable in low pinning superconductors in the frequency range ∼ 100 Hz to ∼ 10 kHz.