Abstract:
The n-value is an important superconducting parameter, which represents the homogeneity of
characterized superconductor as well as thermally activated depinning. In addition n-values are
important for the evaluation of pinning mechanisms and pinning forces. n-values are crucial input
parameters for the numerical simulations of superconducting tapes, coils and other complicated
superconducting applications where E-J power law applies. In this publication, complex measurement
data of n-values from different 2nd generation of high temperature superconducting (2G HTS) tapes
are presented and analysed. In addition, 2G HTS tapes were step by step irradiated by fast neutron
fluences up to 1x1022 m-2 . n-values of the irradiated tapes, containing additional randomly distributed
pinning centres, are presented, analysed and compared with unirradiated samples. Special attention is
placed on the underlying physics resulting in power-law part of the I-V curve and on the correlation
between critical currents and n-values. The measurements are performed within the temperature
range of 50 K-85 K and magnetic fields up to 15 T.
