Self-Field Effects on JC(B,T) Measurements of Nb–Ti Strands in High Magnetic Fields

We have investigated the applied magnetic field, temperature, and self-field dependence of the critical current density of a Nb-Ti strand produced for the ITER poloidal field conductor. Measurements were made on a standard ITER barrel in magnetic fields from 4.0 to 8.0 T and temperatures from 3.5 to 6.0 K. We investigated the effect of self-field by changing the direction of the transport current, resulting in an inward or outward Lorentz force acting on the strand. At 4.2 K and 5 T, the difference in the measured J
_C
between the two Lorentz force polarities was about 1%. From this low value, we conclude that self-field effects in the Nb-Ti strand are about 40% of those expected using standard self-field calculations for fully transposed multifilamentary strands, consistent with theoretical considerations for annular filament transposition.