Possibility of effect of electric charge on the stability of current-carrying high-field superconductors

The charge-diffusion length lambda(/sub Q/ in the flux-pinned superconducting region near the interface between the pinned region and dissipative region is estimated from published experimental data on the minimum current I/sub r/ for SN-boundary propagation in Nb-Ti composite conductors. The estimation gives lambda(/sub Q/approx. =3.2--3.9 μm irrespective of the variety of conductor shape and structure, applied magnetic field, and cooling conditions. This result reveals the possibility that the gap depression by the accumulated charge at the interface with a flux-depinning effect is the determining factor in the dynamics of the SN boundary in composite superconductors