SBIR-STTR Award

Controlled chemical doping of magnesium diboride (MgB2) has been shown to substantially improve superconducting properties to the levels required for high field magnets, but 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. Gas phase plasma synthesis of boron powder in which dopants and boron are atomically mixed in the plasma will produce nano-sized batches of doped boron powder. Initial experiments using plasma synthesis methods proved satisfactory to prepare carbon-doped boron powders suitable for the fabrication of high performance MgB2 conductors. At 20 K, critical current density (Jc) values of 100,000 A/cm2 were obtained at 2 Tesla and at 5 K, Jc values of 100,000 A/cm2 were obtained at 4-5 Tesla. Upper critical magnetic field (Hc2) values as high as 37 tesla were achieved. In Phase I, an investigation of carbon, titanium, and silicon carbide as dopant additions to boron powder will be carried out to improve on the above properties. The plasma synthesis method will be used for powder production and the effect of dopant chemistry and concentration on the properties of boron powder will be examined. Doped boron powder will be converted to MgB2 superconducting pellets and powder-in-tube wires, and the superconducting properties will be measured. The effect of powder particle size, purity, dopant concentration, and chemical homogeneity on the superconducting properties of MgB2 will be investigated. Chemically doped magnesium diboride (MgB2) superconducting magnets can perform at least as well as NbTi and NbSn3 in high field magnetic fields and still offer an improvement over the latter in terms of operating temperature. These characteristics make doped MgB2 an effective material for medical MRI devices. Cheaper and more efficient medical MRI devices could lower examination costs, find potential health problems earlier, and thus benefit society as a whole.

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The availability of magnetic resonance imaging (MRI) scanners is having a significant impact on public health, and greater availability of these units in the US and throughout the world is desired. A primary factor limiting availability is the existing superconductor magnet technology. Presently, commercial MRI magnets require liquid helium (LHe);however, the world's helium supply is decreasing and the price is increasing. As a result, MRI producers are pushing to develop MRI systems based on LHe-free magnesium diboride (MgB2) superconducting magnets. The goal of this project is to develop doped boron nanopowder made by a plasma synthesis process to be used for producing MgB2. Phase I of this project was highly successful. The plasma synthesis process was scaled from a 10 gram laboratory method to a greater than 200 gram process that can produce the kilometer length wires needed for preliminary evaluation of MRI magnets. Wires made from carbon-doped boron nanopowder had critical current densities, Jc, of greater than 105 A/cm2 out to 8 tesla. These are the world's highest performing MgB2 superconductor wires reported to date. This significant improvement exceeded the goals of the program and makes 1.5 and 3 Tesla MRIs based on MgB2 magnets viable in the near-term (3-5 years). The Phase II specific aims are 1) produce multiple kilogram quantities of doped boron nanopowder and use it to fabricate longer lengths of MgB2 wires;2) scale up the plasma synthesis process for boron nanopowder by increasing the long-term stability and capacity of the plasma synthesis system;and 3) further develop and scale up a vapor-solid synthesis process to make MgB2 nano-sized powder. Specialty Materials, Inc. will complete the work necessary to develop the plasma synthesis process to produce kilogram-sized batches of boron nanopowder that can be used to fabricate multi-kilometer wires needed for commercial MRI magnets. MgB2 nanopowder development will provide risk mitigation by providing raw material for both in situ and ex situ fabrication of MgB2 wires. This project will be carried out in close collaboration with wire fabricators and MRI end users so that the next generation of MRI scanners based on MgB2 superconducting magnets can be commercialized in a 3-5 year timeframe.

Public Health Relevance:
This project will develop boron nanopowder, the most critical raw material for the next generation of magnetic resonance imaging (MRI) scanners based on magnesium diboride (MgB2) magnets. These new MRI scanners will be much less costly, more efficient, more portable, capable of diagnosing medical problems earlier and faster, and will be much more widely available throughout the country and world.

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