Investigation of the levitation force of field-cooled YBCO and MgB₂disks as functions of temperature

Abstract

We report levitation force cycles resulting from measurements carried out on a YBCO and a MgB2 disk cooled down in the field of a permanent magnet. In both cases the amplitude of the levitation force tends toward maximum values as the temperature decreases. Otherwise, the cycles are almost closed at low temperature and strongly hysteretic in the high temperature range. The hysteresis of the force cycles is attributed to the distribution of the currents induced in the sample by the field of the magnet. The saturation of the levitation forces at low temperature is related to that of the magnetic moment of the disks. We show that this type of measurement allows for the determination of the critical current density of superconductors in a restricted domain of temperatures.

The Measurement and Modeling of the Levitation Force Between Single-Grain YBCO Bulk Superconductors and Permanent Magnets

“…We report that negative force up to 2 N were measured during the ascending run at higher temperature produced by the deeper penetration of currents. Negative force during the ascending run is also reported by other authors [17], [20], [30] 3. Currents of the descending runs (successive to the first) completely wipe out currents of the ascending runs.…”

“…Characterization is essential for the development of levitating systems based on (RE)BCO bulks. Furthermore, numerical modeling is required for understanding the electrodynamics of the observed levitation phenomena and for predicting and optimizing the performance of systems of practical interest [10]- [20]. Numerical modeling also provides a way for Automatically generated dates of receipt and acceptance will be placed here; authors do not produce these dates.…”

“…deducing, by the fitting of the experimental data, the critical current density of the material based on the measured levitation force [20]. In this paper, the levitation force between a permanent magnet (PM) and a single grain YBCO sample is investigated experimentally and numerically in the temperature range 30 K -80 K. The paper is organized as follows: the experimental apparatus used for the measurement of the levitation force in field cooling and zero field cooling conditions is described in section II.…”

Determination of the Complete Penetration Magnetic Field of a HTS Pellet From the Measurements of the Magnetic Field at Its Top-Center Surface

“…The influence of JC(B) of this BP, n-value and JC determination method has to be studied further in next studies to improve the relevance of our method. The comparison of this method with previous ones [13]- [15] has to be done too. …”

“…5 represents the distributions of J/JC in a HTS pellet for three different Vb (0.1T/s, 10T/s and 1000T/s) for the same value of Ba. In these simulations the n-value chosen is 15, that is a weak n-value for HTS at 77K [11][12][13][14][15], JC is constant and equals to 100 A/mm². As shown in Fig.…”