Flux pinning and flux flow studies in superconductors using flux flow noise techniques. Progress report, April 1-December 30, 1979

Flux flow noise power spectra were investigated, and information obtained through such spectra is applied to describe flux flow and pinning in situations where volume pinning force data is also available. In one case, the application of noise data to PB/sub 80/In/sub 20/ samples after recovery and after high temperature annealing is discussed. This work is consistent with a recent model for flux flow noise generation. In the second case we discuss experiments designed to change the fluxoid transit path length, which according to the model should affect both the noise amplitude and the parameter ..cap alpha.. specifying the longest subpulse times in terms of the average transit time, tau/sub c/. Transient flux flow voltages when a current is switched on after field cycling a Pb/sub 60/In/sub 40/ sample have been discovered. Noise spectra have been measured during the transient. These observations are discussed along with a simple model which fits the data. A surprising result is that the transient decay times increase with the applied current. Other characteristics of Pb/sub 60/In/sub 40/ after cold working are also discussed