Modelling the Energy Losses of a Superconducting Magnetic Bearing due to the Change of the Levitation Height Under Gravity

This paper describes the losses of the rotor of the prototype superconducting magnetic bearing (SMB) that is employed for a polarization modulator of a Cosmic Microwave Background polarization experiment. The stator is composed of 20 segmented YBCO bulks, and these multiple superconductors produce the inhomogeneous magnetic field particularly due to the gravitational displacement of the rotor magnet position from the initial field cooling. This inhomogeneity causes the power dissipation to the spinning rotor. We estimated the power dissipation originating from this inhomogeneous magnetic field by using a numerical approach. The superconductors were modelled as electrically conducting components in the numerical simulation to avoid the complexity in modelling superconductivity. The results show about 4 mW dissipated at the rotor. (paper)