Levitation Performance of Bulk High Temperature Superconductor Above the Permanent Magnet Guideway at Different Temperatures

The levitation performance of a high temperature superconducting (HTS) Maglev system was investigated at different temperatures for HTS Maglev vehicle application. Using a cryogenic measurement system, we studied the effects of the HTS’s temperatures and the HTS’s field-cooling heights (FCHs) on the levitation force and its force density by applying a two-pole Halbach array’s permanent magnet guideway (PMG) at different temperatures. Results show that the levitation force is not only dependent on the temperature but also dependent on the original FCH. The effect of the temperature on the levitation force is considerably minute in low FCH. However, it was confirmed that the levitation force of HTS is larger at a lower temperature than at a higher temperature in high FCHs. Moreover, by applying the temperature of 60 K, the levitation force density of the system can be increased by 65% and 57.3% compared to the force density at 77 K in 35 mm and 40 mm FCHs. Hence, more magnetic energy at a low temperature area and high FCH can be utilized. The advancement of Maglev system’s performance will directly promote the development of HTS Maglev application and is helpful for the further HTS Maglev vehicle.     

A Method to Increase the Lateral Reversible Region of Bulk YBCO Above a Permanent Magnet Guideway

Lateral reversible region of the bulk high-T _c superconductor (HTSC) above the permanent magnet guideway (PMG) is a key parameter for the high-T _c superconducting (HTS) maglev system. The lateral stability and guidance force are proportional to the width of the lateral reversible region. When the lateral displacement of the bulk HTSC exceeds the reversible region, the maglev system will return to a new lateral equilibrium position. The method with the use of pre-displacement can successfully increases the lateral reversible region of the bulk HTSC. By the correct choice of the maximum lateral offset and a new starting point, the instability of flux motion can be suppressed. Unsuitable usage of this method will cause the intersection of guidance force and reduce the reversible region. Analyses based on the magnetizing history and pinning metamorphoses well explain the experimental results. Difference between this method and the pre-load method is also discussed in this article.     

3D-Modeling Numerical Solutions of Electromagnetic Behavior of HTSC Bulk above Permanent Magnetic Guideway

This paper presents a 3D-modeling numerical method using finite element method (FEM) to simulate the electromagnetic behavior of high-temperature superconductors (HTSC). The models are formulated by the magnetic field vector method (H-method). The resolving code was written by FROTRAN language. The electromagnetic properties of HTSC are described though Kim critical-state model. The magnetic fields and current distribution in the bulk HTSC in the applied non-uniform external magnetic fields generated by the permanent magnetic guideway (PMG) are obtained using the proposed method. The magnetic levitation forces by the interaction between the bulk HTSC and the PMG are calculated. In order to validate the method, measurement of the vertical force between a bulk YBaCuO(YBCO) and a PMG is obtained. The measurement and simulation results show good matching. This method could be used in the HTSC magnetic levitation transportation system optimization design.      

A Simulation on Levitation Force and Guidance Force of the HTSC Bulk Under the Permanent Magnetic Guideway’s Stochastic Excitation

Journal of Superconductivity and Novel Magnetism - In the actual operation of the high temperature superconducting (HTSC) maglev, due to the irregularity of the permanent magnetic guideway (PMG),...     

Dynamic Simulation of High Temperature Superconductors Above a Spinning Circular Permanent Magnetic Guideway

Before a high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle system can be fully applied and operational, the study of its dynamic characteristics is necessary. With the developed HTS Maglev dynamic measurement system (SCML-03), with a circular permanent magnet guideway (PMG) of 1.5 m in diameter, the vehicle’s translational motion above a PMG can be effectively simulated with the PMG allowed to rotate freely. Levitation force measurements of a high temperature superconductor (HTSC) array of seven YBa₂Cu₃O_7−x bulks were carried out above regular (linear) and a simulated (circular) PMG. The levitation force above a linear PMG segment and a circular PMG segment in the static state is found to be in good agreement with each other. The levitation force in the dynamic state is found to slowly attenuate since the presence of a rotating circular PMG below the HTS array is found to be analogous to the application of an AC external magnetic field.     

An Asymmetrical Permanent Magnet Guideway Design for the High Temperature Superconducting Maglev Curve

An asymmetrical permanent magnet guideway (PMG) design is considered for the high temperature superconducting (HTS) Maglev during traveling on a curved path. This translationally asymmetrical PMG design can produce a better guidance performance, which cannot be provided by the common translationally symmetrical PMG design. The additional guidance improvement is attributed to its asymmetrical magnetic field distribution. The outside part of the asymmetrical PMG has more magnetic material than the inside part, so that the outside magnetic field density is enhanced or becomes a multi-pole distribution. These two effects result in a larger guidance force and a better curve negotiation ability. Above the asymmetrical curved PMG, the HTS Maglev vehicle system can overcome larger centrifugal forces and run with a smaller or even zero lateral displacement. Moreover, this asymmetrical PMG design is helpful to realize the “straight line to curve to straight line” running environment. The improvement effect and running feasibility of the asymmetrical PMG is calculated and proven for future use in HTS Maglev curves.     

Effect of AC Magnetic Field on the Levitation Force of YBCO Bulk above NdFeB Guideway

In the present High Temperature Superconducting (HTS) maglev vehicle system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneous of the material property of the NdFeB magnet. In order to investigate the influence of the nonuniformity on the levitation performance of the HTS bulk, an electromagnet supplied by AC current is used to simulate the nonuniformity of the external magnetic field. The levitation force of the HTS bulk is measured when applying AC currents to the electromagnet coils. Experimental results indicate that the levitation force changes abruptly and then oscillates after applying AC external magnetic field, and the levitation force is attenuated by the AC magnetic field after withdrawing the AC field. Moreover, the oscillation amplitude and the attenuation rate of the levitation force increase with the amplitude of the AC external magnetic field.     

Vibrations of an infinitely long flowing liquid jet—Influence of spin and axial flow

For an infinitely long liquid column the influence of axial flow velocity and spin has been investigated. The results are exhibited for axisymmetric mode m=0 and asymmetric modes m=1 and 2. A frictionless liquid shows with the increase of axial flow an increase of the frequency in flow direction and a decrease of the oscillation frequency in the opposite flow direction for axisymmetric motion. It also means that a larger surface tension, larger diameter or larger density of the liquid column exhibit the same behavior. For asymmetric motions the effect of axial velocity w₀ is the opposite. With increasing axial wave length the natural frequencies decrease. At certain axial speed magnitudes both waves move in flow direction with different magnitude. The effect of increasing spin is a decrease of natural frequencies and an instability for smaller axial wave lengths. Viscous effects show usually smaller oscillation frequencies.     

Magnetic Forces Relaxation Step Change Characteristics of YBCO Bulk with Mechanical Impact Load over a NdFeB Guideway

Magnetic force relaxation of YBCO bulk above the NdFeB permanent magnet guideway (PMG) with impact load has been investigated. An experimental setup has been built using a single YBCO bulk and a symmetrical center NdFeB PMG. There are two experimental methods: the case of magnetic levitation force relaxation measuring perturbed with impact load in zero-field-cooling (ZFC); and the case of magnetic levitation and guidance force relaxation measuring synchronously perturbed with impact load in field-cooling (FC). The results show that there is magnetic levitation and guidance forces relaxation step change at the time of the impact load. Two times impact loads are applied for each method. The first step change range is much larger than the second one. The Bean critical model and Anderson–Kim theory are used to analyze it.     

The Influence of the Morphology on the Magnetic Properties of Poly(3-hexylthiophene)

The influence of the morphology on the magnetic properties of poly(3-hexylthiophene) has been studied and the results reported. The changes in the saturation magnetization were explained considering the polymer morphology prepared with different amounts of water in the solution during sample synthesis. The results show that the saturation magnetization is maximized for 200 ppm of the water in acetonitrile solution.     

Experimental Studies of the Influence of a High‐Frequency Electromagnetic Field on the Convection of Fluids in a Vertical Tube

Results of experimental studies of the influence of a highfrequency electromagnetic field on a change in the levels of fluids in a vertical tube are reported.     

Temperature Characteristics of Platinum–Cobalt Resistance Thermometers Based on the ITS-90 Above 14 K

Three platinum–cobalt resistance thermometers (PtCoRTs), which are manufactured in a structure similar to a capsule-type standard platinum resistance thermometer (SPRT), were calibrated against the capsule-type SPRTs, which was calibrated based on the International Temperature Scale of 1990 (ITS-90) at NMIJ. The thermometers were calibrated in the temperature range from the triple point of equilibrium hydrogen to the triple point of water by using the dissemination system of the ITS-90 at NMIJ. In this study, the temperature dependence of the resistance ratio, \(W\) , which is the ratio of the resistance obtained at each temperature by the calibration to the resistance at the triple point of water, is obtained for each PtCoRT. In the temperature region below the triple point of Ne, the temperature dependence of \(W\) of each PtCoRT is fitted by a 4th-order polynomial. In the temperature region above the triple point of Ne, a 13th-order polynomial is fitted to the temperature dependence of \(W\) . It was found that residuals for the polynomial fits of each PtCoRT were less than 0.3 mK in both temperature regions.     

Influence of Ageing Heat Treatment on the High Cycle Fatigue of an 8090 Al-Li Alloy

Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue life in comparison with natural ageing. On the contrary, the notched specimens of 8090 alloy in the naturally aged condition show higher fatigue life than in the peak-aged. The exposure to either the peak-aged or naturally aged leads to superior fatigue properties of Al-Li alloy to the traditional high strength aluminum alloys of 7075 and 2024, especially in the latter aged condition. In all ageing conditions, i,e. naturally, under-, peak- and over-aged, the peak-aged 8090 alloy displays the highest fatigue life and the over-aged material has a minimum value at the same stress amplitude. The difference in fatigue life is mainly attributable to the size and distribution of strengthening precipitates as well as the wide of precipitate free zones (PFZ's) along grain boundaries.     

Application of an Electro-Magnetic Induction Technique for the Magnetization up to 100 T in a Vertical Single-turn Coil System

The system was developed for the magnetization measurement in the vertical single-turn coil (V-STC) system at ISSP, which can generate magnetic fields over 100 T in a semi-destructive manner. We have adjusted the electro-magnetic induction method to our V-STC. The new system was applied to the manganite with the perovskite-type structure Bi_1/2Ca_1/2MnO₃. The total magnetization process was obtained up to 105 T in excellent quality comparable to those obtained by the non-destructive long pulse magnet.     

Direct Measurement of the Critical Velocity Above Which a Tuning Fork Generates Turbulence in Superfluid Helium

The dynamics of an electrically-driven 8 kHz quartz tuning fork has been studied experimentally in liquid helium-4 in the temperature range 1.3<T<4.2 K under the saturated vapour pressure. The fork has relatively large dimensions compared to standard 32 kHz fork used in recent investigations. The velocity of the tip of the fork prong is measured by the indirect electromechanical equivalent method and is compared with the velocity of another 8 kHz fork (from the same batch) determined by direct optical measurement of the oscillation amplitude through Michelson interferometry. A comparison of these results has provided absolute values for the critical velocity of the transition to the turbulent state.     

Ferromagnetic- and Superconducting-Like Behavior of the Electrical Resistance of an Inhomogeneous Graphite Flake

We have measured the magnetic field and temperature dependence of the resistivity of several micrometers long and heterogeneously thick graphite sample. The magnetoresistance results for fields applied nearly parallel to the graphene planes show both granular superconducting behavior and the existence of magnetic order in the sample.     

Measurement of Thermodynamic Temperature Above the Silver Point on the Basis of the Scheme n?=?2

In this article, a practical n = 2 scheme, fitting into the ??Mise en pratique for the definition of the kelvin?? (MeP-K) at high temperature: MeP-K-HT is presented. It is made up by selected, intertwined pairs of reference points with one common lower reference point, the copper point, all in all constituting a main range and five associated subranges. The upper reference point associated with a given subrange can be chosen in conformity with the application. As will be shown, the proposed scheme has the following advantages when disseminating and measuring T: high intrinsic robustness, flexibility in coverage of temperature??in conformity with the application??effectiveness in terms of accuracy, and efficiency in terms of expenditure. The n = 2 scheme, as proposed, would be a good candidate for an officially endorsed successor or at least an endorsed complement to ITS-90 above the silver point. This would not exclude any other scheme in conformity with the MeP-K-HT being put into practice, like??reversing the argument??the still officially endorsed ITS-90 is to be allowed for the time being as one of the means for implementing MeP-K-HT.     

The Decay of a Quantized Vortex Ring and the Influence of Tracer Particles

We capture the decay of a quantized vortex ring in superfluid helium-4 by imaging particles trapped on the vortex core. The ring shrinks in time, providing direct evidence for the dissipation of energy in the superfluid. The ring with trapped particles collapses more slowly than predicted by an available theory, but the collapse rate can be predicted correctly if the trapping of the particles on the core is taken into account. We theoretically explore the conditions under which particles may be considered passive tracers of quantized vortices and estimate, in particular, that their dynamics on the large-scale is largely unaffected by the burden of trapped particles if the latter are spaced by more than ten particle diameters along the vortex core, at temperatures between 1.5 K and 2.1 K.     

Influence of Additive Silica on the Laser Melting of the Ceramic Coatings

The influence of additive silica on the microstructure of plasma sprayed Al2O3 and Al2O3 13 wt pct TiO2 ceramic coatings at laser melting has been investigated in this study ,At the laser melting ,additive silica in Al2O3ceramic coating can reduce the stress of cooling shrinkage generated during solidification ,Moreover,silica can render finer size of grains of the melting layer and form continuous glassy matter around the grain boundaries so as to reduce further the cooling stresses and to suppress the formation and spreading of cracks ,On the other hand,at the laser melting,TiO2 reacts with Al2O3 and transforms into TiAl2O5,The latter new phase has great and anisotropic coefficients of thermal expansion leading to big and asymmetrical stresses and thus to form cracks in the melting layer of Al2O3 13 wt pct TiO2 coating ,Due to the fact that the influence of additive silica on the suppression of the formation of cracks is rather limited and cannot counterbalance the negative effect of TiAl2O5,thus the melting layer of Al2O3 13 wt pct TiO2 coating doped with 3 wt pct SiO2 cracks also ,Nevertheless,TiO2 can greatly develop the wear resistance of the ceramic coating as sprayed or laser melted.     

Influence of Laser Coating on Microstructure and Properties of an Al-Si Alloy

The microstructure and wear resistance of acast Al-Si alloy coated with metal and rare earthelements and treated by the laser rapidmelt-solidification(LRMS)are studied in the pres-ent work.Optical and SEM micrographic analysesshowed that a superfine microstructure was ob-tained,and the hardness was remarkably enhancedby the LRMS treatment.Wear test showed that therapid melt-solidified microstructure had higherwear resistance than that treated by ordinary solidsolution treatment.