Optimization of levitation forces [in superconducting magnetic bearings]

In this contribution, the authors present a systematic approach to the calculation of levitation forces in plane-parallel (infinitely extended in one direction) arrangements of permanent magnets and superconductors. Starting from an extremely idealized geometry with a very simple expression for the levitation force, they go step by step to more realistic arrangements and present the corrections in the force equations. In particular, magnet configurations with an increased field gradient which allow a higher stiffness are investigated. Finally, numerical calculations are presented which show the dependance of the levitation force on the size and the critical current density of the superconductor and the effect of magnet-iron combinations instead of magnets without iron. The calculations show that the stiffness can be increased by using magnets which consist of several sections with alternating polarity. However, this improvement can only be used for reduced bearing gaps and increased critical current density. The use of magnet-iron combinations has only little advantage.