Hollow carbon spheres as an efficient dopant for enhancing critical current density of MgB2 based tapes

A significant enhancement of Jc and Hirr in MgB2 tapes has been achieved by the in situ powder-in-tube method utilizing hollow carbon spheres (HCS) as dopants. At 4.2 K, the transport Jc for the 850C sintered samples reached 3.1x10^4, and 1.4x10^4 A/cm^2 at 10 and 12 T, respectively, and were better than those of optimal nano-SiC doped tapes. Furthermore, the Hirr for doped sample was raised up to 16.8 T at 10 K due to the carbon substitution effect. The results demonstrate that HCS is one of the most promising dopants besides nano-carbon and SiC for the enhancement of current capacity for MgB2 in high fields.Comment: 14 pages, 5 figure

Pinning mechanism and engineering critical current density considerations in the design of MgB2superconducting coils

Superconducting coils are designed for the generation of specified magnetic fields (low, intermediate, or high). To function in different field regimes, it is important to analyze the pinning mechanics and the types of pinning centers in the superconductor in a precisely defined magnetic field. Correct identification of pinning centers would allow for the formulation of approaches to increase the critical current density and critical magnetic field, ultimately making it possible to reduce the cost of producing superconducting coils (with smaller amounts of wire needed). This paper will present a method to analyze pinning centers in MgB superconductor wires in low, intermediate, and high magnetic fields at 4.2 K, 20 K, 25 K, and 30 K. This method allows us to elucidate the influences of doping, isostatic pressure, and reduction of the wire diameter on individual pinning centers in a specific magnetic field. In this article, we also show a method to analyze the types of pinning centers and their impact on the engineering critical current density (J). This method not only allows for the identification of the types of pinning centers, but also identifies which type allows for a shift in the J criterion of 100 A/mm to enable higher magnetic fields