Current-carrying capacity of composite superconductors

The maximum transport current I
m
of the composite superconductors is investigated both theoretically and experimentally. It is shown that the high values of the transport current observed in these materials is due to the non-linear part of the current-voltage characteristic in the range of low electric fields (
E \lsim 10^{-6}
Vcm
^-1
). The conductors of rather different structure with Nb-Ti superconducting filaments were tested in a wide range of the external parameters. It is shown that in the external magnetic fields
B_{a} \gsim 1 T
the ratio I
m
/I
c
(where I
c
is the critical current) is the universal function of the single dimensionless parameter which depends on the sample properties and the external conditions. The theory and experiment are in a good agreement.