Guangtong Ma

Method to reduce levitation force decay of the bulk HTSC above the NdFeB guideway due to lateral movement

A magnetic levitation vehicle using bulk high-Tc superconductors (HTSC) is considered as a promising transportation type thanks to its lateral inherent stability, but previous studies have found that the levitation force (LF) decays due to lateral movement. In this paper, a pre-load method is presented to reduce the LF decay, and the experimental results indicate that this method is very applicable in supressing this decay in spite of the applied field and material property of the bulk HTSC, and this effect can be ascribed to the reduction of the hysteresis loss in the bulk HTSC, i.e. more trapped magnetic flux after the pre-load case. In the end, experimental results indicate that the Halbach PMG has an advantage to reduce the cost of the PMG, but its rate of LF decay is also larger due to lateral movement

3-D Modeling of High-

A magnetic levitation technique with high-Tc superconductor (HTS) has received significant interest for a wide range of applications after its discovery due to its unique inherent stability, which gives a fundamental significance to evaluate the HTS magnetic levitation in both experiment and calculation. To numerically investigate the HTS magnetic levitation, a 3-D model describing the electromagnetic property of the HTS, including its anisotropic behavior, was established by incorporating the current vector potential and Helmholtzs theorem. In addition to the commonly considered nonlinear E-J characteristic in the reported calculation, we introduce an elliptical model to formulate the angular dependence of the critical current density Jc resulting from the anisotropic behavior of the HTS. To numerically resolve the governing equations of the 3-D model, Galerkins finite-element method and the Crank-Nicolson-θ method were employed to discretize the governing equations in space and time domains, respectively. The obtained algebraic equations were firstly linearized by the Newton-Raphson method, and then an extended format of the incomplete Cholesky-conjugate gradient method was applied to solve the linear algebraic equations. The 3-D model was implemented by a self-written numerical program based on a VC++ platform to calculate the magnetic force of a bulk HTS exposed to applied field generated by a permanent magnet guideway (PMG) assembled by the Nd-Fe-B magnets. In this paper, we present the numerical results of the levitation force of a moving bulk HTS above the PMG with different mesh densities and number of time steps. This presents a preliminary validation of the 3-D model proposed in this paper.

T_{c}

In this paper, the 3-D model proposed in Part I of this study is verified in detail on the basis of a levitation/suspension system composed of a rectangular single-domain Y-Ba-Cu-O and a cylindrical Nd-Fe-B magnet or a permanent magnet guideway (PMG) assembled by the Nd-Fe-B magnets. The magnetic forces along the vertical direction perpendicular or the transverse direction parallel to the surface of the PMG (or magnet) were calculated and compared well with the measured data under vertical and transverse displacements. The computed results of the induced current distribution within the Y-Ba-Cu-O domain, as well as the magnetic field profiles in the Y-Ba-Cu-O and its vicinal region, were also presented and discussed.

Superconductor for Magnetic Levitation/Suspension Application—Part I: Introduction to the Method

A robust and fast numerical course for investigating the magnetic levitation (maglev) performance of high-temperature superconductors (HTSs) is proposed and implemented via finite-element methods (FEMs) in this paper. This numerical course uses the magnetic vector potential as the state variable to establish the partial differential equations (PDEs) for governing the electromagnetic properties of 2-D simplified HTSs, a smoothed Bean-Kims model of a critical state to describe the nonlinear constitutive law of HTSs, and the advanced algorithm of Jacobian-free Newton-Krylov (JFNK) to handle the nonlinear system of the FEM equation. After being tested, this homemade FEM model was applied to investigate the influence of various FEM parameters, e.g., the dimension of the computational domain, the prescribed tolerance for convergence, the coarseness of the mesh, and the time step, upon the precision of levitation/guidance force on an HTS bulk while moving in a nonuniform field generated by a permanent-magnet track. The most important findings through these studies are that the coarse choice of tolerance can cause the nonphysical phenomena such as the crossings in the force loops, and the numerical results are very robust against the dimension of the computational domain, the coarseness of the mesh, and the time step. Based on these findings, it was found that the time consumed for performing a typical cycle of levitation force calculation is merely a few seconds, making the application of this FEM model for optimizing the HTS maglev system very attractive.

3-D Modeling of High-

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.

T_{c}

A four pole superconducting excitation system that was part of a linear synchronous motor (LSM) system, was fabricated and its thrust and normal forces studied experimentally. Four cases were investigated, air-cored, with a ferromagnetic (FM) back plate, an FM core, and with both an FM back plate and core. With a total of only 15 m of YBCO coated conductor in the form of four coils as the excitation system, thrust output of up to 95 N while operating at 77 K with a magnetic gap of 10 mm was obtained in one particular case. The results of the studied superconducting LSM system help better understand the feasibility of their applications to drive systems for Maglev trains.

Superconductor for Magnetic Levitation/Suspension Application—Part II: Validation With Experiment

By the introduction of a generalized magnetic vector potential, which contains the contributions of both the magnetic and electric parts, and the use of the Amperes law within the quasistatic approximation as the state equation, the partial differential equations for governing the electromagnetic properties of superconductors as well as the surrounding coolant were established and numerically discretized by resorting to the finite-element technique and finite-difference scheme, respectively, in the spatial and temporal domain. In conjunction with an analytic method to calculate the magnetic field generated by permanent magnet, we compiled a numerical tool for performing an intricate study of the mutual effect among the superconducting constituents in a superconducting levitation system with translational symmetry. Taking a superconducting unit with three constituents inside as a practice, we simulated the electromagnetic responses of this unit while moving in the nonuniform magnetic field generated by pe...

Considerations on the Finite-Element Simulation of High-Temperature Superconductors for Magnetic Levitation Purposes

Four coils made of YBCO-coated conductor wire were fabricated and connected in series to make up the excitation system of a linear synchronous motor system with a stator made of ordinary copper wire. The electromagnetic forces experienced by the superconducting coils with respect to the stator were studied in the static case. We began with the study of one single coil, followed by two coils connected in series, and finally, four coils in series from which the largest force obtained was of 53.9 N at a gap of 10 mm at 77 K. The critical current, n-value, and inductance were also measured for the coils so that the power dissipation of the field windings can be calculated. This paper also helps us understand whether linear motors with superconducting components are currently economically feasible with present commercially available superconducting wire.

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

Numerical simulations of the hysteretic ac loss in a coated superconductor with a more realistic version of the architecture were performed via the finite-element technique in the presence of an oscillating magnetic field. The coated superconductor was electromagnetically modeled by resorting to the quasistatic approximation of a vector potential approach in conjunction with nonlinear descriptions of the superconducting layer and the ferromagnetic substrate therein by a power-law model and the Langevin equation, respectively. A diverse effect of the ferromagnetic substrate on the hysteretic ac loss, depending on the strength of the applied magnetic field, was displayed, and its underlying cause was identified. The dependence of the hysteretic ac loss on the applied frequency is found to be related to a critical amplitude of the applied magnetic field, and the eddy-current loss dissipated in the metal coatings becomes prominent as the frequency increases only at high applied magnetic fields.

Superconducting Excitation System of a Small Scale Linear Synchronous Motor

The mechanical bearing in the cryogenic liquid pump has short working life due to the low temperature environment. For conquering the disadvantage, the radial high temperature superconducting magnetic bearing (HTSB) is designed to be used in the cryogenic pump. The high temperature superconductors (HTSs) in the HTSB are cooled by the cryogenic liquid directly. The introduced cryogenic liquid pump can constrain the heat leakage. The equipment for the kinetic characteristics of the HTSB is introduced, and it can measure the axial forces of the HTS at different rotation speeds. Basic mechanical principle of the rotor of the pump is analyzed.