An apparatus includes an annular rotor that rotates about a rotational axis. A magnetic bearing system influences the position of the annular rotor in three-dimensional space and includes at least three actuators, wherein at least one actuator generates a force for lifting the annular rotor in a vertical direction, at least one actuator influences the position of the annular rotor in the radial direction of the annular rotor and at least assists in maintaining an annular gap between at least one non-magnetic bearing and the annular rotor during operation and at least one actuator influences the position of the annular rotor in an axial direction of the annular rotor. At least one radiation source may be fixedly mounted on the annular rotor.