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Öğe Comparative study of the magnetic stiffness, levitation and guidance force properties of single and multi seeded YBCOs for different HTS-PMG arrangements(Elsevier Ltd, 2015) Ozturk K.; Sahin E.; Abdioglu M.; Kabaer M.; Celik S.; Yanmaz E.; Kucukomeroglu T.Abstract It is crucial to improve the magnetic levitation, guidance and stiffness performances of the HTS Maglev systems for real-scale applications. In this study, the magnetic levitation force, guidance force and magnetic stiffness values were determined for single and multi-seeded YBCOs on different PMGs in ZFC regime and different cooling heights (CHs) after the magnetic flux distributions simulation of the using PMGs. Implemented study showed that the additional downward PMs make an enhancing contribution on the magnetic levitation force, guidance force and magnetic stiffness of both single and multi-seeded YBCOs. It was also determined that both the force and stiffness ratios of multi-seeded YBCO to single-seeded YBCO increase with increasing CH, indicating that the multi-seeded YBCO has much more interaction domain than single-seeded at higher gaps. It is considered that the results obtained in this study are very useful in technological applications of Maglev and bearing systems, because there is no detailed study on the magnetic stiffness, levitation and guidance force comparison to clarify electromagnetic behavior of single and multi-seeded YBCOs for different HTS-PMG arrangements. © 2015 Elsevier B.V.Öğe Comparison of Levitation Forces of Bulk MgB2 Superconductors Produced by Nano Boron and Carbon-Doped Nano Boron(Springer New York LLC, 2014) Duz I.; Guner S.B.; Erdem O.; Demir I.; Kapucu V.; Çelik Ş.; Ozturk K.; Hossain S.; Gencer A.; Yanmaz E.MgB2 bulk superconductors were prepared by hot press plus furnace heating method. Two types of boron powders were used, one is amorphous nano boron and the other is C-doped boron. Characteristics of superconductors were determined by XRD and resistance measurements. Systematic levitation force measurements were performed by using a modular system at low temperatures. These bulk superconductors showed around 9 N repulsive and 4 N attractive forces in the z-axis at 20 K at closest point to the cryostat lid which contains the MgB2 superconductor. These values slightly decreased by increasing temperature to 24 and 28 K for both samples. Comparing two samples, nano boron MgB2 showed slightly higher levitation force than C-doped MgB2 although C-doped MgB2 has higher attractive force value at the closest point. This situation points out that C-doped MgB2 is much proper for attractive force applications (as guidance force) while the nanoboron MgB2 sample is much appropriate for repulsive force (as levitation). © 2014, Springer Science+Business Media New York.Öğe Effect of Er doping on the superconducting properties of porous MgB2(Indian Academy of Sciences, 2015) Erdem O.; Yanmaz E.MgB2 bulk sample with porous structure was produced by using the in-situ solid-state reaction method under argon (Ar) atmosphere of 10 bar. Elemental Er in powder form was doped into MgB2 with different compositions (Mg1-xErx)B2, where x = 0.00, 0.03 and 0.05, in order to investigate the effect of rare-earth (RE) element Er on the structural and electromagnetic properties of porous MgB2. The Er-doped samples result in small grain size structure compared to the undoped one. The lattice constants a and c of the doped samples, determined from X-ray diffraction (XRD) analysis, increase with the increasing Er content, and consequently the superconducting transition temperature (Tonsetc) of MgB2, determined from resistivity measurements, is slightly suppressed. Also, the upper critical field (Bc2), the irreversibility field (Birr) and the critical current density (Jc) values are significantly enhanced in the doped samples. For the best sample (x = 0.03), at 15 K under a magnetic field of 4 T, the Jc value reaches 2.4×104 A cm-2, which is higher than that of the porous sample by an order of 103, and the Birr value at 20 K reaches 9.7 T. These results imply that the RE element Er fills the pores, enhances the density and the grain connectivity. Hence, the superconducting properties of the porous MgB2 sample improve by Er doping.Öğe Effect of laser irradiation on activation energy, irreversibility field and upper critical magnetic field of bulk MgB2 superconductor(Springer New York LLC, 2016) Erdem O.; Yanmaz E.In this study, the role of laser irradiation on the upper critical field (Hc2), the irreversibility field (Hirr) and the activation energy (U0) of bulk MgB2 superconductor was first time investigated with the aid of magnetoresistivity measurements conducted at different applied magnetic fields in a range of 0–15 kOe as a function of temperature from 25 to 40 K. For this aim, a disk shaped MgB2 superconductor was produced and cut into two pieces. One of the pieces was irradiated under high vacuum conditions by using an Nd:YVO4 laser. The obtained results showed an increase in the critical temperature (Tc) by about 1 K after irradiation. Also, the values of Hc2(0) were respectively found to be around 143 and 151 kOe while the values of Hirr(0) were about 122 and 130 kOe for the reference and the irradiated samples. Using the thermally activated flux flow model the dependence of U0 on magnetic field was determined. The maximum U0 values of 0.43 and 0.83 eV in zero magnetic field were respectively obtained for the reference and the irradiated samples. Also, the magnetic field dependence of the critical current density Jc(B) values at different temperatures were slightly increased after the irradiation. These results point out that the superconducting properties of bulk MgB2 can be improved via laser irradiation. © 2016, Springer Science+Business Media New York.Öğe Effect of laser irradiation on superconducting properties of bulk MgB2 sintered at different temperatures(Springer New York LLC, 2017) Erdem O.; Yanmaz E.The surfaces of MgB2 bulk samples produced by a pellet/closed tube method at two different sintering temperatures of 650 and 850 °C, after hot pressing at 200 °C, were irradiated with the same irradiation dose by using an Nd:YVO4 laser in order to study the possible potentiality of laser irradiation to improve pinning performances and critical current density of MgB2 superconductor. The measurements showed that the magnetic field dependence of the critical current density values of irradiated sample sintered at 650 °C slightly increased with a narrowing in superconducting transition region as compared to the reference sample sintered at same temperature. However, irradiated sample sintered at 850 °C showed a decrease in pinning performance and similar critical temperature values as compared to the corresponding reference sample. From these results it can be said that the same laser irradiation dose affects superconducting properties of bulk MgB2 in different ways depending on sintering temperature of the superconductor. © 2017, Springer Science+Business Media New York.Öğe Effect of magnetic flux distribution and magnetic powder addition on the magnetic levitation force of Sm123 superconductors(2012) Abdioglu M.; Ozturk K.; Kutuk S.; Bolat S.; Yanmaz E.Sm123 and Sm211 were prepared by melt-powder-melt-growth and solid-state-reaction techniques, respectively, to have the nominal composition of (Sm123) 0.75 (Sm211) 0.25. After the preparation of this composition, the Fe-B magnetic powder (MP) was added to the composition for 0.000, 0.010, 0.015, 0.025, 0.050 wt.% to investigate the effect of MP addition on the levitation force density (LFD). Additionally, different permanent magnets (PM) were used as magnetic-field source to investigate the effect of magnetic-field gradient on the LFD of MP added superconductors. Our findings indicate that the MP addition acts as a flux pinning centre in the sample and enhances the LFD up to 0.025 wt.% adding amount, and the optimum flux gradient which produces a screening current in the sample occurs when the B/d (magnetic-field intensity/ diameter of PM) ratio is equal to 0.060. These results imply that the experimental data can be useful for fabricating process of superconducting samples with larger MLF values, and designing of superconducting magnets, flywheel energy storage and maglev systems. © 2012 Springer Science+Business Media, LLC.Öğe Effects of initial cooling conditions and measurement heights on the levitation performance of bulk MgB2 superconductor at different measurement temperatures(Springer New York LLC, 2014) Erdem O.; Ozturk K.; Guner S.B.; Celik S.; Yanmaz E.The levitation properties of MgB2 prepared by hot press at 200 ° C and then pellet/closed tube method has been investigated. The vertical and lateral levitation forces (Fz and Fx) on a cylindrical NdFeB permanent magnet (PM) below a disk-shaped bulk MgB2 were measured during the vertical and lateral traverses of the PM in different cooling heights (CHs) and measurement heights (MHs) at temperatures of 20, 25 and 30 K to investigate the effect of the initial CH and MH on the levitation performance of MgB2. For temperatures below 30 K, it was observed that Fz increases with increasing CH. However, a minute variation in Fz and a big hysteresis loop are observed at 30 K. From the lateral traverses, it was obtained that the Fz with attractive character increases with decreasing MH and the hysteresis effect increases for small MHs due to the increment of the magnetic field intensity which the sample feels with decreasing MH. In addition, it was seen that the character of Fx varies depending on both MH and measurement temperature. The higher hysteresis obtained in Fx than in Fz during lateral traverses implies that the motion of the flux lines in MgB2 is especially in lateral rather than vertical direction. Finally in this study, it was shown that the levitation performance of MgB2 depends not only on the measurement temperature but also on the CH and MH conditions. These results can be useful for optimizing the levitation performance of MgB2 superconductors for potential applications. © 2014 Springer Science+Business Media New York.Öğe Enhanced Pinning Properties of Laser-Irradiated Bulk MgB2 Superconductors(Springer New York LLC, 2017) Erdem O.; Yanmaz E.In order to investigate the effect of laser irradiation on the superconducting properties of MgB2, a pellet-shaped sample was produced and cut into two pieces. The dot-shaped molten patterns, with the distance of 100 µm between them, were formed on the surface of one of the pieces by using an Nd:YVO4 laser. The grains of the irradiated sample were significantly grown due to the laser-induced sintering. The modified surface appeared to have dense and compacted grains as a result of increasing interconnectivity among the superconducting grains. The critical current densities at 5 K in a field of 3 T were found to be 5.38 × 104 and 8.96 × 104 A cm?2 for the reference and the irradiated samples, respectively. The increment of critical current density for the irradiated sample is presumably connected with the changing of pinning mechanism after the laser irradiation. For the irradiated sample which showed a higher value of critical current density at 5 K under high fields, ?? pinning was obtained as a dominant pinning mechanism, while the normal point pinning was dominant for the reference one. These results point out that the superconducting properties of bulk MgB2 can be changed and improved via laser irradiation in a short time. © 2016, Springer Science+Business Media New York.
