The critical current density of advanced internal-Mg-diffusion-processed MgB2wires

Recent advances in MgB 2 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 MgB 2 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 MgB 2 layer structure was observed. The best layer J c for our sample is 1.07 × 10 5 A cm −2 at 10 T, 4.2 K, and our best J e is seen to be 1.67 × 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 MgB 2 layer growth mechanism.