Demagnetization of Cubic Gd-Ba-Cu-O Bulk Superconductor by Crossed-Fields: Measurements and Three-Dimensional Modeling

Abstract

Superconducting bulks, acting as high-field permanent magnets, are promising for many applications. An important effect in bulk permanent magnets is crossed-field demagnetization, which can reduce the magnetic field in superconductors due to relatively small transverse fields. Crossedfield demagnetization has not been studied in sample shapes such as rectangular prisms or cubes. This contribution presents a study based on both 3D numerical modelling and experiments. We study a cubic Gd-Ba-Cu-O bulk superconductor sample of size 6 mm magnetized by field cooling in an external field of around 1.3 T, which is later submitted to crossed-field magnetic fields of up to 164 mT. Modelling results agree with experiments, except at transverse fields 50% or above of the initial trapped field. The current paths present a strong 3D nature. For instance, at the mid-plane perpendicular to the initial magnetizing field, the current density in this direction changes smoothly from the critical magnitude, Jc, at the lateral sides to zero at a certain penetration depth. This indicates a rotation of the current density with magnitude Jc, and hence force free effects like flux cutting are expected to play a significant role.

Cross-field demagnetization of stacks of tapes: 3D modelling and measurements

“…In our stack, the penetration front contains both the penetrates from the top and bottom of each individual tape. This is the same qualitative behavior found for superconducting bulks [30]. The oscillations in the current profiles in figure 10(e,f) are due to numerical error.…”

“…A more detailed trapped field profile is calculated along the (red) line B t above the sample on figure 13 (a). The profile has the usual symmetric peak at the end of the relaxation time shift, contrary to cubic bulk samples [30]. The cause of this difference is the thin film shape of tapes, as follows.…”

Fast Fourier transform-based solution of 2D and 3D magnetization problems in type-II superconductivity

“…Appearance of a significant z component of j , necessary for shielding the zero-field core, is an unexpected feature of current density distribution discovered and explained in [16][17][18]. We found that smoothing, employed in the FFT-based method, smears the narrow peaks of z j and, therefore, had to use a weaker Gaussian filter with 0.5d   to arrive at the z j -distribution ( Figure 6) similar to that in [19].…”

Coupling loss at the end connections of REBCO stacks: 2D modelling and measurement

“…Althgough, uncoupled stacks (and coils) and fully coupled stacks have been well studied by many researchers before, the case of an intermediate finite resistance ("partial coupling") has not been previously studied for stacks of tapes. Previous studes focused on ac loss under perpendicular magnetic field [19][20][21][22][23][24][25][26][27], ac loss under transport current [28][29][30][31][32], ac loss with consideration of ferromagnetic material [33][34][35][36], dynamic resistance under various applied field [37][38][39][40], magnetization and decay of trapped magnetic field [41][42][43][44][45][46][47][48], multifilamentary calculations [19,49], among other topics. Thanks to the presented numerical 2D MEMEP model, this article systematically studies and discusses the amplitude-dependence, frequency-dependence, and resistance-dependence of coupling loss under parallel magnetic field.…”