In pulsed field magnetization (PFM), the phenomenon of flux jump is capable of driving magnetic flux vortexes into GdBCO superconducting bulk center to aid full magnetization. Varieties of homogeneous critical current density (Jc) models have been implemented to reproduce flux jumps, but simulated multi-physical responses differ from experimental observations. This paper proposes a modified Jc model to consider r-z plane Jc inhomogeneity and simulates flux jumps under experimental conditions by solving a 2D axisymmetric electromagnetic-thermal coupled model. A numerical treatment is developed to reflect the break of shielding current during flux jumps. The accuracy of our model is verified by comparisons of the calculation results of trapped magnetic fields (BT) and the PFM and field cooling (FC) experimental results. On this basis, we investigate the improvement of inhomogeneous Jc model and obtain the multi-physical responses which have better agreement with the experimental results compared to homogeneous Jc model. Moreover, to further test the ability of the inhomogeneous Jc model to predict anisotropy of spatially magnetic field distribution, the simulated BT profiles in top and bottom surfaces of HTS bulk at 77 K are compared to the experiments. This study may provide a new approach for modelling the inhomogeneity of Jc characteristics and a useful analysis tool for industrial devices using high-temperature superconductor (HTS) bulk magnets.

Characterized by very low rotational drag, applications of high temperature superconductor (HTS) bearings have been expanded in some high precision instruments. We developed a sensitive magnetic suspension stand based on an Evershed-type hybrid HTS bearing to measure the micro newton level thrust. The hybrid HTS bearing is to use the strong attractive force of a permanent magnet (PM) biased bearing to support main loading in the bearing, while the instability in the PM biased bearing was compensated by the magnetic stability from an HTS bearing. Compared to the single PM/HTS bearing, the hybrid HTS bearing is intended not only to support larger load and but also to suppress the rotation loss and levitation drift. Loading capacity, loss and damping torque were explored at different design parameters such as bearing gaps L1, L2, field cooling height (FCH) of bulk HTSs. Spin down testing suggested that the loss of the hybrid HTS bearing can be reduced by raising the HTS bearing gap L2 or reducing the field cooling height. The hybrid HTS bearing showed a typical oscillation behavior in the extreme low frequency, and torsional pendulum testing suggested that the spring constant k of the hybrid HTS bearing can be as low as 36.39 μN·m/°. A micro-thrust stand based on the hybrid HTS bearing was established to test an electrospray thruster in the vacuum chamber, and the measurement result of 26.61 μN presents the ability of micro-thrust stand to achieve μN level testing.

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Benefited from the combination of Messiner effect and flux pinning, a permanent magnet (PM) can give the self-stable levitation above a bulk superconductor. The phenomenon provides the basic principle of superconductors in wide applications such as HTS maglev trains and superconducting flywheel systems. When the superconductor works under some conditions without the flux pinning (for example zero-field cooling), the PM will show free motion along multi freedoms due to the full diamagnetism of superconductor. This paper investigated the drag characteristics of the PM moved above the diamagnetic plane spliced by superconducting bulks. The spliced diamagnetic plane can get rid of the limitation of the size of the single superconducting bulk, and realize low-drag translational motion levitation in a large area. The article builds a multidimensional levitation force measurement device to measure the vertical force and lateral force of the PM translation when the superconducting plane works at different temperature. It is found that the lateral force distribution in the PM translation shows with alternating peaks and valleys. The increase of the suspending air gap can reduce the lateral force fluctuation and realize low-drag translation. The translational lateral force has the smaller value at the center of a single superconducting block, and can be measured at the level less than 1mN. The low drag characteristics bring the potential application of superconducting translational levitation in the low gravity ground simulation for attitude and orbit control experiments of satellites