Plasma Synthesized Doped Boron Nanopowder for MgB2 Superconductors

Controlled chemical doping of magnesium diboride (MgB2) has been shown to substantially improve superconducting properties to the levels required for high field magnets. However, consistent dopant concentrations and homogeneity are difficult to accomplish through the usual route of solid state reaction and diffusion. Furthermore, a high quality source of doped boron needs to be established to advance the state of the art and to ultimately commercialize MgB2 superconductors. This project will prepare carbon-doped boron powders suitable for the fabrication of high performance MgB2 conductors. In Phase I, a gas-phase plasma synthesis method was investigated for producing doped-boron nanopowders suitable for use in commercially viable MgB2 superconductor wire. Boron powder, doped with carbon and titanium, was converted to MgB2 superconducting pellets and multifilament powder-in-tube (PIT) wires, and superconducting properties were measured. The effect of certain parameters (such as dopant level, powder particle size, and wire processing temperature) on the superconducting properties was determined. The carbon-doped MgB2 was fabricated into 19-filament wires and yielded an upper critical magnetic field of 37T, equal to the highest values yet attained for bulk MgB2 materials. In Phase II, carbon, titanium, and silicon carbide will be investigated as dopants and optimum compositions will be defined. The effect of powder particle size, purity, dopant concentration, and chemical homogeneity on the superconducting properties of MgB2 will be determined. Fundamental plasma processing parameters for the optimal synthesis of the boron nanopowders will be developed. Commercial Applications and Other Benefits as described by the awardee: Chemically doped MgB2 superconducting magnets should perform at least as well as NbTi and Nb3Sn in high field magnetic fields, with an improvement in terms of operating temperature. MgB2 should thus become an effective material for high magnetic field applications, such as for particle accelerators, confined fusion, and medical MRI devices. Cheaper and more efficient medical MRI devices could lower examination costs and detect potential health problems earlier.