Current distribution and ac susceptibility response of a thin superconducting disc in an axial field: a theoretical approach

Within the framework of the thermally activated process of the flux line or flux line bundles, and by time integration of the 1D equation of motion of the circulating current density (J) over right arrow(rho, t), which is sui table for thin superconducting films (R >> d, less than or equal to lambda) , we present numerical calculations of the current profiles, magnetization hysteresis loops and ac susceptibility chi(n) = chi(n)(') + i chi(n)(") for n = 1, 3 and 5 of a thin disc immersed in an axial time-dependent external magnetic field B-a (t) = B-dc + B-ac cos(2 pi nu t). Our calculated result s are compared with those of the critical state model (CSM) and found to pr ove the approximate validity of the CSM below the irreversibility field. Th e differences between our computed results and those of the CSM are also di scussed.