  Recent advances in MgB2 conductors are leading to a new level of performance.
Based on the use of proper powders, proper chemistry, and an architecture which
incorporates internal Mg diffusion (IMD), a dense MgB2 structure with not only
a high critical current density Jc, but also a high engineering critical
current density, Je, can be obtained. In this paper, a series of these advanced
(or second - generation, "2G") conductors has been prepared. Scanning electron
microscopy and associated energy dispersive X-ray spectroscopy were applied to
characterize the microstructures and compositions of the wires, and a dense
MgB2 layer structure was observed. The best layer Jc for our sample is 1.07x105
A/cm2 at 10 T, 4.2 K, and our best Je is seen to be 1.67x104 A/cm2 at 10 T, 4.2
K. Optimization of the transport properties of these advanced wires is
discussed in terms of B-powder choice, area fraction, and the MgB2 layer growth
mechanism.
