Chang-Qing Ye

Geometrical Effects on the Levitation Capability of Multiseeded Y–Ba–Cu–O Blocks

Using a well-established theoretical model to calculate the levitation behavior of multiple high-temperature superconductors, the levitation capability of multiseeded Y-Ba-Cu-O blocks over two promising permanent-magnet guideways (PMGs) was evaluated and its dependence on the number of seeds was clearly displayed. The multiseeded Y-Ba-Cu-O blocks are ideally supposed to be composed of a set of single domains that are magnetically coupled but electrically insulated, which means we only consider the intragrain current. This assumption is a prerequisite for avoiding the complexity of assessing the morphology of the intergrain current, which is actually weaker than the intragrain current due to the unsolved obstacles in material process such as the weak link of grain boundary that impedes the current transfer across the grains. The insights attained by this numerical study, being inaccessible from experiments, tell us that, given the width of the Y-Ba-Cu-O block, the levitation force is found to be mostly degraded as the number of the seeds increases or the width of each seed decreases, whereas the lateral force exhibits a more complex behavior.

Cloaking the Static Magnetic Fields by Alternate Superconductor–Ferromagnet Heterostructure

The novel concept to well cloak the incident static magnetic fields by a heterostructure made of a superconductor (SC) and a ferromagnet (FM) has been proposed and verified recently. The performance of such heterostructure strongly depends on the involved materials and its geometrical configurations. We designed and built a practical version of a cylindrical multilayer cloak wound by an alternate SC-FM heterostructure that consists of a coated superconductor and a 1Cr17 ferromagnetic alloy. The cloaking properties of such hybrid against the static magnetic field generated by a Helmholtz coil were measured to verify the related finite-element model, in which the SC constituent is postulated as a diamagnet with relative permeability of less than 1. Using the verified model, we further carried out a set of finite-element simulations with experimentally derived permeability of both the SC and FM constituents to observe the dependence of the cloaking effect as well as the shielding efficiency of the SC-FM heterostructure on its geometry. The obtained characteristics of the magnetic cloaking of the SC-FM hybrid may offer a new paradigm for its applications in the military and medical devices.

Calculation and Optimization of High-Temperature Superconducting Levitation by a Vector Potential Method

We have theoretically established and experimentally validated a vector potential method for calculating the magnetic forces of high-temperature superconductor (HTS) subject to nonuniform magnetic fields generated by a permanent-magnet guideway (PMG). The highlight of the proposed method beyond the traditional approaches is that we introduced an auxiliary variable to represent both the magnetic vector potential and the electric scalar potential, which makes the calculation of superconducting levitation in 2-D space very efficient. By using the time-step finite-element technique to perform the spatial and temporal discretizations, the proposed mathematical model was numerically implemented and validated in a comprehensive manner by the measured data as well as the calculated data with other method. Enabled by the efficiency and robustness of the proposed method, we further incorporated this method into a genetic algorithm, and developed an intelligent scheme for optimizing the HTS maglev transportation system to realize a cost-efficient design. Using the maglev system, with one HTS levitated over a Halbach-derived PMG as a representative, we finally carried out a set of optimization studies to understand how the working condition and geometrical and material characteristics of the HTS affect its achievable levitation capability at different constraints of the cross-sectional area of PMG.

Levitation Performance of a Magnetized Bulk YBCO With Different Demagnetization Processes

The magnetized bulk high- superconductor (MBSCM) can provide dramatic improvements towards the levitation performance of HTS Maglev systems if sufficient and suitable magnetic excitation methods are employed. In the field-cooling excitation mode, the demagnetization process greatly influences the levitation performance of the MBSCM in some special operation modes. A difference in the levitation performance was observed from experimental tests under different demagnetization field strengths and rates. Simulation based on finite element method was used to calculate the temperature rise within the MBSCM during the studied demagnetization process. With experimental results and analyses, an optimal demagnetization process for the MBSCM for engineering applications was derived.

Intelligent Optimization of an HTS Maglev System With Translational Symmetry

Optimization is essential to reduce the cost of high-temperature superconducting (HTS) maglev systems composed of a permanent magnetic guideway (PMG) and an HTS unit and thus promote their application. In this paper, the geometrical shape of a Halbach-derived PMG is optimized via an intelligent genetic algorithm to devise a more cost-effective system. We compute the levitation force of the HTS unit above the PMG with self-made finite-element codes, using the Kim-Bean current-voltage relationship in the governing equation of the 2-D model of HTS maglev system. Then, we introduce how the genetic algorithm is coupled with this 2-D model. Taking the levitation force of the HTS unit at a vertical distance above the PMG as the objective function, considering some practical geometry and cost constraints, we optimized a kind of Halbach-derived PMG. This optimization approach can provide a more general rule for the future design of the HTS Maglev system.

Numerical Modeling and Transient Analysis of a Linear Induction Motor With Close-Ended Coated Superconductor Coils as Secondary

We devised a linear induction motor (LIM) that uses the close-ended coated superconductor coils as the secondary to explore the potential solutions of enhancing the thrust performance at large clearance, which is generally required for the linear propulsion of transit systems. In this proposal, the coated superconductor coils are embedded into a ferromagnetic yoke whose function is to guide and concentrate the travelling fields generated by the three-phase conventional stator. To make a preliminary study before the laboratory demonstration, we built a numerical model of this proposal by resorting to the finite-element software of MagNet, a recognized professional tool to simulate the electrical machines in the scientific community. Through a treatment of the power law, the developed numerical model has included the nonlinear constitutive law of superconductor, which is currently thought to be difficult in the MagNet environment. This general treatment takes a step forward toward the use of the professional software to perform complex simulations of the superconducting machines. Based on the numerical model, we carried out a set of transient studies on the proposed LIM to observe the distributions of travelling flux, the starting characteristics, and the time evolutions of thrust and speed. The achieved results clearly display that the proposed LIM has advantages over the conventional type and could be thereby regarded as a candidate for developing high thrust linear LIM with large clearance.

Design Optimization of a Heavy-Load High-Temperature Superconducting Maglev System With Multiseeded YBaCuO Bulks

Multiseeded YBaCuO bulk crystallized by melt growth process is usually employed as the levitated magnet in high-temperature superconducting (HTS) maglev system. However, to the state of art, the intergrain supercurrent between different domains in the multiseeded bulk superconductor is much harder to simulate than the intragrain supercurrent in the single-seeded bulk, hindering the numerical study of multiseeded bulks. In this paper, we first discussed how to simulate the electromagnetic response of multiseeded bulk superconductor levitated above permanent magnetic guideway (PMG) through treating the multiseeded bulk as magnetically coupling but electric uncoupling domains, discriminating from assuming it as a single-seeded bulk superconductor. This model was validated through experiments of a three-seeded bulk levitated at different positions above a Halbach-derived PMG, comparing with a single-seeded bulk with the same geometrical dimensions. To realize a heavy-load HTS maglev system that can carry over a ton per meter length of levitation constituent, we introduced the feasible paths to increase the load, increasing the volumes of superconductors and PMs. We also optimized the selective configurations of the HTS maglev system by the genetic algorithm to reduce the total cost. The final summarized rules for designing the heavy-load HTS maglev system applied multiseeded bulk superconductors and Halbach-derived PMGs are deemed important to industrial-level application.