Critical Current Density and Current Transfer Length of Multifilamentary MgB2 Strands of Various Design

In this paper, a series of high performing PIT MgB2 strands have been prepared. Transport voltage-current measurements were performed to determine the effects of C doping and strand geometry such as filament numbers. The best Jc for our samples was 1.0 × 105 A/cm2 at 4.2 K, 7 T, for a strand using B powder with 3% C addition. The current transfer length (CTL) was also measured for MgB2 short wires with Nb chemical barrier and Monel outer sheath. The CTL ranged from 2-12 mm, and had a correlation with the filament numbers.This work was supported by the U.S. Department of Energy, High Energy Physics grant DE-FG02-95ER40900, and a DOE SBIR.The in-field critical current densities of a set of in situ CTFF-type PIT MgB2 strands have been investigated in terms of C doping level, wire diameter and filament number. The strand with optimal doping level – 3% C achieved the best Jc of 1.0 × 105 A/cm2 at 4.2 K, 7 T. By fitting it with the percolation model, the parameters showed that the Bc2 and the flux pinning strength was improved and the anisotropy ratio was reduced. Increases in filament count did not change Jc, although n-values were higher for the monocore strand. The current transfer length of MgB2 strands with Nb chemical barriers and Monel sheaths increased with filament count. The CTL was less than 3.7 mm for the monocore strand, and it ranged from 2.2-11.8 mm for the 24- filamentary strand D2, depending on the applied field