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Most of the latest models of HTS bulk magnetization take into account the thermal and electromagnetic coupling, but, they still lack the implementation of the mechanical deformation under strong magnetic fields. The following work tries to fill up partly the gap by proposing a model of the dependence of the electrical conductivity upon mechanical deformation during field-cooling magnetization. This dependence is carried out by the critical current density as a function of induced thermal and mechanical strain in the bulk. As a first approximation and bearing in mind the obvious discrepancies, a simplemodel inferred from HTS thin films and generic knowledge on ceramics is proposed. This first approach allows drawing some generalities on the expected thermal, magnetic, and mechanical response of disk-shaped YBCO pellets during magnetization. The utter goal is to assess design parameters to insert those pellets in electrical rotatory machines. [ABSTRACT FROM AUTHOR]

In this paper, we propose to study and design a coil used to magnetize, by means of a pulsed fieldmagnetization (PFM) process, an inductor of a radial flux superconducting machine with one pair of poles. Each pole contains four similar high-temperature superconducting (HTS) bulks of 30 mm diameter arranged in a square pattern. The cryostat already exists for this application and the temperature of the HTS bulks can vary from 4.2 K to their critical temperature, in a transient state. For a given primary source of energy, here a capacitor bank of 10 kJ (5mF, 2 kV) is available, the PFM process depends strongly on the value of the coil inductance used to generate pulsed field, because it defines the waveform of the current: peak value and time constant. Thus, three-dimensional modeling of the coil is required in order to be sure that its inductance and the magnetic field produced will provide a full magnetization of HTS bulks. From the practical point of view, we would like to achieve an average magnetization of each pole around 3 T. In this paper, numericalmodeling of coils with different number of turns coupled with circuit's equations is achieved. The maximum magnetic field obtained on the HTS bulks and estimated magnetization at the top center of each HTS bulk, are presented and discussed. [ABSTRACT FROM AUTHOR]

A robust numerical method based on 2-D mixed finite-elements-finite volumes (FE-FV) allows the solution of diffusion problems in superconducting (SC) materials. The proposed approach handles the strong nonlinearity of the E(J) constitutive power law of high-temperature superconductors (HTS). The method is tested for a SC cylinder submitted to a sinusoidal transport current or to a transverse sinusoidal external field. The current density distributions as well as the AC losses are computed. Comparisons to a FE analyses that use the magnetic field as state variable show the validity of the proposed approach. It can be seen that the proposed method is very stable even for large n-values for which the FE method does not converge. [ABSTRACT FROM AUTHOR]

It is well known that the critical current density JC of a superconducting material depends on the magnetic flux density B. For practical applications, it is essential to have accurate information about JC(B), which can be obtained from different experimental techniques (transport current, hysteretic cycle, and ac susceptibility). This paper presents a simple and quick JC(B) experimental determination method for a superconducting cylinder. A first JC(B) experimental evaluation method consists of measuring the magnetization cycle M(B) and determining the width of this cycle for each value of B. This is generally done using the Bean model, where JC is considered constant. A more accurate method is presented in this paper. The cylinder first magnetization curve M1(B) is calculated with the Kim model [JC(B) = JC0/(1 + (|B|/BC0))] and with a linear model and compared with the measured first magnetization curve M1mea(B). In so doing, JC0 and BC0 are determined, and the results obtained using both JC (B) determination methods are compared and discussed. [ABSTRACT FROM AUTHOR]

An original superconducting synchronous motor topology is presented. The inductor combines both bulk materials and wires to create an alternating magnetic field in the air gap of the motor. A prototype that uses NbTi superconducting wires and YBCO bulks has successfully been designed and constructed. Test results are presented. In the second part of this paper, the possibility of higher power motor is discussed. To do so, the active length needs to be increased. In this paper, a multistack structure is proposed, and computation results show the effectiveness of the suggested approach. [ABSTRACT FROM AUTHOR]

This paper presents a new numerical method based on finite elements finite volumes (FE-FV) for solving 2-D diffusion problems in high temperature superconductors (HTS). The approach does not involve directly the resistivity term (p), generally used to model the E(J) characteristic as a power law, i.e E(J) = p(J)J, with p(J) α Jn-1 Instead, we use a J(E) constitutive law J α E(1/n) with →E= E→e z (a single component), which leads to a scalar non-linear differential equation. After presenting in details the developments, the method is tested in the case of a superconducting cylinder submitted to a transverse magnetic field. The current density obtained is compared to another numerical technique (the semi-analytical method) in order to validate the results. Although not fully optimized yet, it appears that the proposed method is very stable, especially for large n-values (greater than 100). [ABSTRACT FROM AUTHOR]

To use high-Tc superconductors for alternating current transport, it is important to evaluate AC losses. The influence of .Jc(13) on the self field losses in a superconductive tube fed by a transport current in incomplete penetration is studied for two reasons. First, superconducting power cables have a geometry that resembles a tube and second, for high-temperature superconductors, the variation of .Jc(B) is important especially for low magnetic fields like self field. An analytical calculation of the distribution of the magnetic field B(r, t) by using a linearized law Jc(B) is presented. From B(r, t) one deduces .J(r, t) and E(r, t). The analytical expressions of those were used to calculate the analytical instantaneous power p(t). The losses in the superconducting tube are the average value of p(t). They are numerically calculated and compared with the measurements taken on a sample whose characteristic Jc(B) was previously measured. With the linear model, the calculated losses are closer to the measured losses than for the Bean model, but the Jc(B) identification remains the main problem. [ABSTRACT FROM AUTHOR]

It is well known that the critical current density Jc of a superconducting material depends on the magnetic flux density B. There exists an electric method to measure the Jc(B) deduced from the U(I) measurements. The problem with this method is the self field effect because the magnetic flux density is always the sum of the applied magnetic flux density and the self magnetic flux density. This paper presents a special experimental arrangement, compensating fully or partially the self magnetic flux density in an HTS tube. It allows characterizing the true zero magnetic flux density behaviour of the superconducting material. The experimental results of the compensation are discussed. A theoretical analysis based on Bean's model is presented and gives results close to the experimental ones. The proposed compensation is not perfect but the experiments and the theoretical analysis allow validation of the compensation principle. [ABSTRACT FROM AUTHOR]

This paper deals with the cooling of the rotor of a superconducting motor. We consider three cooling systems: a cold insert, circulation of a cool gas and boiling of a cool liquid. For each case, we study the use of three different gases: hydrogen, helium, neon, and two liquids: hydrogen and neon. For each case of cooling, we define the best gases in term of cooling efficiency. [ABSTRACT FROM AUTHOR]

We have designed, constructed and tested an eight-pole superconducting rotating machine, based on an unconventional topology that could potentially lead to a significant increase in power density. Calculations have been carried out in two steps: estimation of the magnetic scalar potential from a Coulomb formulation using the Markov chain Monte Carlo (MCMC) method, and the calculation of the flux density by derivation of the potential using a regularization method. The use of the MCMC method enables the calculation of the magnetic scalar potential in selected regions of the discrete geometry, which is an important factor to minimize the computation time. The principle of the operation has been validated by a successful testing of the motor showing this novel configuration of electrical an motor as very promising. [ABSTRACT FROM AUTHOR]