The use of an MgB2 hollow cylinder and pulse magnetized (RE)BCO bulk for magnetic levitation applications

Both MgB2 and (RE)BCO bulk materials can provide a highly compact source of magnetic field when magnetized. The properties of these materials when magnetized by a pulsed field are potentially useful for a number of applications, including magnetic levitation. This paper reports on pulsed field magnetization of single 25 mm diameter (RE)BCO bulks using a recently constructed pulse magnetization facility, which allows an automated sequence of pulses to be delivered. The facility allows measurement of force between a magnetized (RE)BCO bulk and a bulk MgB2 hollow cylinder, which is field cooled in the field of the magnetized (RE)BCO bulk. Hysteresis cycling behavior for small displacement is also measured to extract the stiffness value. The levitation forces up to 500 N were obtained, the highest ever measured between two bulks and proves the concept of a bulk-bulk superconducting bearing design. © 2002-2011 IEEE.

Magnetotransport study of MgB2 superconductor

Precise magnetotransport studies of heat and charge carriers in polycrystalline MgB2 show that magnetic fields up to 8 T remarkably influence electrical resistivity, thermoelectric power and thermal conductivity. The superconducting transition temperature shifts from 39 K to 19 K at 8 T as observed on electric signals. The temperature transition width is weakly broadened. Electron and phonon contributions to the thermal conductivity are separated and discussed. The Debye temperature calculated from a phonon drag thermoelectric power component is inconsistent with values derived through other effects.

Fishtail effects and improved critical current density in polycrystalline bulk MgB2 containing carbon nanotubes

Bulk, polycrystalline MgB2 samples containing 2.5 wt.% multi-walled carbon nanotubes (CNTs) have been prepared by conventional solid state reaction at 800 °C. The effect of Mg precursor powders composed of two different particle sizes on the critical current density (Jc) of the as-sintered samples has been investigated. An enhancement of Jc at high field has been observed in MgB2 samples containing CNTs prepared with fine Mg powders, whereas the values of Jc in the sample prepared using the coarser Mg powders was slightly decreased. These results contrast significantly with measurements on pure, undoped, MgB2 samples prepared from the same Mg precursor powders. They suggest that carbon substitution into the MgB2 lattice, which accounts for increased flux pinning, and therefore Jc, is more effective in precursor Mg powders with a larger surface area. Rather surprisingly, the so-called fishtail effect, observed typically in MgB2 single crystals and in the (RE)BCO family of high temperature superconductors (HTSs), was observed in both sets of CNT-containing polycrystalline samples as a result of lattice defects associated with C substitution. Significantly, analytical fits to the data for each sample suggest that the same flux pinning mechanism accounts for the fishtail effect in polycrystalline MgB2 and (RE)BCO. © 2013 Elsevier B.V. All rights reserved.

Magneto-Optical Imaging of Superconductors for Liquid Hydrogen Applications

Restricted deposits of fossil fuels and ecological problems created by their extensive use require a transition to renewable energy resources and clean fuel free from emissions of CO2. This fuel is likely to be liquid hydrogen. An important feature of liquid hydrogen is that it allows wide use of superconductivity. Superconductors provide compactness, high efficiency, savings in energy and a range of new applications not possible with other materials. The benefits of superconductivity justify use of low temperatures and facilitate development of fossil-free energy economy. The widespread use of superconductors requires a simple and reliable technique to monitor their properties. Magneto-optical imaging (MOI) is currently the only direct technique allowing visualization of the superconducting properties of materials. We report the application of this technique to key superconducting materials suitable for the hydrogen economy: MgB2 and high temperature superconductors (HTS) in bulk and thin-film form. The study shows that the MOI technique is well suited to the study of these materials. It demonstrates the advantage of HTS at liquid hydrogen temperatures and emphasizes the benefits of MgB2, in particular. © 2012 Springer Science+Business Media New York.

A thermally actuated superconducting flux pump

The concept of a superconducting flux pump is relatively straightforward. A small magnetic field repeatedly applied will lead to a much larger field being trapped within the superconductor. This field is limited by the volume of the superconductor and by its critical current but not by the excitation field. Here we will describe a new technique which facilitates the creation of high magnetic fields and where the magnitude of the trapped field is limited by the superconductor not the magnetising field. The technique is demonstrated using measurements taken using samples of bulk YBCO as YBCO has a very high irreversibility field and has the potential to trap high magnetic fields. The technique could be applied to other superconductors such as BSCCO or MgB2 and in other forms such as thin or thick films. © 2007 Elsevier B.V. All rights reserved.