•Ermile Gaganidze¹, Michael Fitsilis², Roland Heidinger¹ und Juergen Halbritter^1
1Forschungszentrum Karlsruhe, IMF 1, Postfach 3640, D-76021 Karlsruhe, Germany
²Institut fuer Elektrotechnische Grundlagen der Informatik, University of Karlsruhe, Hertzstrasse 16, D-76187 Karlsruhe, Germany

The application of HTS is obstructed by the nonlinear behavior of Z(T,f,H_rf) with rf field. The study of those nonlinearities profits by carefully calibrated rf measurements in the frequency and time domain, which yield dR_s(H_rf) µ Hⁿ µ dX_s (H_rf). In contrast to dR_s(H_rf) µ Hⁿ, the ratio r = dX_s/dR_s is independent of geometry factors and shows distinct T and f dependencies for various mechanisms and rf set-ups.

The high power rf response in the frequency domain yields nonlinear resonance curves, n and r values. The time domain measurements give useful insight about dynamics of the underlying nonlinear mechanisms. The results r @ 1 and n @ 1-2 are in line with Josephson fluxons in weak links, which may interact with dc fluxons threading through the weak links.

The weak links are quantified by R(T > T_c)-measurements with the help of percolation analysis yielding R_res (T < 0.8 T_c,f) in agreement with observations.