K. Ozturk

The Effect of Magnetic Field Distribution and Pole Array on the Vertical Levitation Force Properties of HTS Maglev Systems

In this paper, the levitation force measurements have been carried out by the magnetic force measurement system under both field-cooling and zero-field-cooling regimes, whereas the magnetic field distribution over the permanent-magnet guideway (PMG) was calculated by numerical analysis based on the finite-element method. It was shown in this study that the vertical levitation capability and stability of Maglev systems can be improved depending on the cooling regime, pole number, and suitable arrangement of the PMG. In this paper, it was shown that when the pole number increases, the levitation force density increases. It also appeared that the reasonable position of the supplementary permanent magnet and appropriate cooling heights are key parameters for both levitation performance and stabilization of the high-temperature superconductor (HTS) Maglev. It is believed that the numerical and experimental data in this paper are useful for relative design and practical application of HTS Maglev systems.

Improvement of superconducting properties of MgB2 by changing the argon ambient pressure and sintering conditions

We have investigated various characteristic properties depending on sintering conditions of MgB2 samples prepared by the standard solid state reaction method. It is inferred from experimental results that the crystallinity of samples were improved when the pressure of the Ar ambient increased. Also, it was found that the sintering temperature above 850 °C caused extremely high amount of decomposition of the superconductor phase. Finally, it was considered that the sintering process of MgB2 must be carried out under the pressure of Ar ambient higher than 8 bar to impede the volatility of Mg in the structure of MgB2. The Jc values of samples systematically enhanced with the increase of sintering time and in particular, the sample sintered for 180 min. exhibited the highest Jc (0) of 4.9 × 103 A cm-2 at 30 K. The obtained results demonstrate that the sintering conditions of MgB2 have a significant influence on Tc (onset) and Jc, which are directly related to practical applications of MgB2 based superconductor components.

Investigation of effect of x in Yb1-xGdxBa2Cu3O7-y superconducting structures on upper critical magnetic field and coherence length

The resistivity measurements of the Yb1-xGdxBa2Cu3O7-y superconducting samples prepared by using the solid-state reaction technique for x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were performed in QD-PPMS system under different magnetic fields up to 5T in zero field cooling regime. The upper magnetic field Hc2(T=0) for each sample was calculated from 50% of the normalized resistivity (Rn) by the extrapolation Hc2(T) to T=0K and the coherence lengths ζ(T=0) of the samples were calculated from the Hc2(0) values. The examination of the effects of x in the composition on Hc2(0) showed us that the upper critical magnetic field decreased from 186.31T for x=0.0 to 37.99T for x=1.0 with the increasing of content x from x=0.0 to 1.0. Using the content x in the composition, the upper critical magnetic field can be controlled and this can be used in superconducting application especially as a superconducting relays.

Anomalous ferromagnetic behaviour of Y2O3 and CuO nanoparticles in YBa2Cu3Oy superconductor

Anomalous ferromagnetic behaviour of the Y2O3 and CuO components in YBa2Cu3Oy (Y123) was observed after severe reduction of particle size. The particle size reduction was performed in following way: Y2O3, BaCO3 and CuO were ground for different times to reduce the particle size to the nanoscale. It was found that the superconducting phase could not be obtained without heat treatment, but a weak ferromagnetic behaviour of the mixture was observed at liquid and room temperatures. In order to understand which compound is responsible for this weak ferromagnetism, the Y2O3, BaCO3 and CuO powders were separately ground and M-H loops taken at 290K. The results indicated that both Y2O3 and CuO powders showed weak ferromagnetism, but BaCO3 showed anti ferromagnetism. It is thought that energy transfer to the powder particles by grinding results in severe plastic deformation of the particles to produce dislocations, vacancies and atomic disorder. We discuss then the observations in the context of recent studies of the magnetic properties of nanoscale oxide materials.