The critical current density of advanced internal-Mg-diffusion-processed MgB2 wires

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, a dense MgB2 structure with not only a high critical current density J(c), but also a high engineering critical current density, J(e), 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 J(c) for our sample is 1.07 x 10(5) A cm(-2) at 10 T, 4.2 K, and our best J(e) is seen to be 1.67 x 10(4) A cm(-2) at 10 T, 4.2 K. Optimization of the transport properties of these advanced wires is discussed in terms of the B powder choice, area fraction, and MgB2 layer growth mechanism.