Stiffness Enhancement of a Superconducting Magnetic Bearing Using Shaped YBCO Bulks

Abstract

High-speed superconducting motors and generators stand to benefit from superconductor magnetic levitation bearings if their stiffness characteristics can be improved. Here we investigate a novel thrust bearing geometry, comprising a conical frustum shaped permanent magnet and matching superconducting toroid and puck assembly, aimed at producing high stiffness coupled with high levitation force. To this end, we have constructed a bearing test rig enabling measurements of the levitation force and stiffness of the assembly of YBa2Cu3O 7−δ melt-textured bulks and Nd2Fe14B permanent magnet at temperatures down to 47 K. The experimental results are supported by finite element modeling that is validated against the experiment, and used to quantify the advantages of this configuration over a conventional cylindrical magnet and HTS puck arrangement. For axial displacements, the assembly produces higher and more consistent stiffness together with stronger restoring forces. For lateral displacements, the assembly produces up to double the lateral force and up to four times the stiffness. Our study also shows that the force contribution to the assembly from the small inner puck is negligible and it can therefore be eliminated from the bearing design.

Angle-dependence of the levitation force from a frustum-shaped magnet and recessed superconducting bulk

“…For θ below about 25 • the curves develop an increasingly convex shape, with the 10 • curve possessing a maximum near z = 6 mm. A similar bell-curve shape was seen previously in our experiments [12] with a frustum/recess angle of 14 • . It stems from the average z-component of the field normally incident on the side walls of the recess changing sign as it the magnet is lowered into the recess.…”

“…Recently, we showed that a levitation bearing based on a conical frustum shaped magnet recessed inside a superconducting bulk provides improved levitation force and lateral stiffness compared to a typical cylindrical magnet and superconductor arrangement [12]. In this follow-on work, we investigate the angle-dependence of the frustum/recess on levitation force, using previously benchmarked H-formulation models, to identify the optimal configuration for this design.…”

Angle-Dependence of the Levitation Force From a Frustum-Shaped Magnet and Recessed Superconducting Bulk

“…For θ below about 25 • the curves develop an increasingly convex shape, with the 10 • curve possessing a maximum near z = 6 mm. A similar bellcurve shape was seen previously in our experiments [12] with a frustum/recess angle of 14 • . It stems from the average zcomponent of the field normally incident on the side walls of the recess changing sign as it the magnet is lowered into the recess.…”

“…Based on our experiments on YBCO high-temperature superconductor bulks [12] the critical current density was set to J c = 21 × 10 8 A/m 2 at the electric field criterion E c = 10 −4 V/m, and the n-value was set to 21. For simplicity a fieldindependent and spatially homogeneous J c was assumed.…”

“…Recently, we showed that a levitation bearing based on a conical frustum shaped magnet recessed inside a superconducting bulk, similar to that shown in Fig. 1(a), provides improved levitation force and lateral stiffness compared to a typical cylindrical magnet and superconductor arrangement [12]. In this follow-on work, we investigate the angle-dependence of the frustum/recess on levitation force, using previously benchmarked H-formulation models, to identify the optimal configuration for this design.…”