Transmission of Magnetic Pulses through Type-II Superconducting Plates

Abstract

The penetration of perpendicular magnetic pulses of 1.6 \ensuremath{\mu}sec duration through a type-II superconducting plate has been observed in a perpendicular magnetic field. The plate was a single crystal of Pb with 8% In and had a thickness of 1.65 mm. For large enough pulses the shape of the transmitted pulse agrees closely with that expected from the diffusion equation $\frac{{\ensuremath{\partial}}^{2}H}{\ensuremath{\partial}{z}^{2}}=\frac{{\ensuremath{\mu}}_{0}\ensuremath{\sigma}\ensuremath{\partial}H}{\ensuremath{\partial}t}$. The time delay of the transmitted pulse as well as the height of the transmitted pulse can be used to find the value of an effective resistivity $\ensuremath{\rho}$. For large pulses the data obtained by the two methods agree with each other and are all somewhat below a line given by $\frac{\ensuremath{\rho}}{{\ensuremath{\rho}}_{n}}=\frac{(H\ensuremath{-}{H}_{c1})}{({H}_{c2}\ensuremath{-}{H}_{c1})}$. Near ${H}_{c1}$ pinning effects are observed: A change $\ensuremath{\Delta}H$ of the superimposed field which aids the pulsed field causes anomalously large pulse penetration. The pulses remain unchanged if $\ensuremath{\Delta}H$ is opposed to the pulsed field. The delay time is not affected by a small change of the superimposed field, indicating that the effective resistivity does not change, but that the change of the superimposed field increases the pressure against the pinning centers and aids the pulse penetration.