  An advanced internal Mg infiltration method (AIMI) in this paper has been
shown to be effective in producing superconducting wires containing dense MgB2
layers with high critical current densities. In this study, the in-field
critical current densities of a series of AIMI-fabricated MgB2 strands were
investigated in terms of C doping levels, heat treatment (HT) time and filament
numbers. The highest layer Jc for our monofilamentary AIMI strands is 1.5 x
10^5 A/cm2 at 10 T, 4.2 K, when the C concentration was 3 mol% and the strand
was heat-treated at 675 {\deg}C for 4 hours. Transport critical currents were
also measured at 4.2 K on short samples and one-meter segments of
eighteen-filament C-doped AIMI strands. The layer Jcs reached 4.3 x 10^5 A/cm2
at 5 T and 7.1 x 10^4 A/cm2 at 10 T, twice as high as those of the best PIT
strands. The analysis of these results indicates that the AIMI strands,
possessing both high layer Jcs and engineering Jes after further optimization,
have strong potential for commercial applications.
