It can be clearly seen from FIG. 1 that the separation element 5 separates the shaft into a first shaft portion 8 and into a second shaft portion 9. To this end, the separation element 5 has a separation portion 10, which extends in the circumferential direction along an inner radius of the shaft 4. A fluid-guiding portion 11 of the separation element 5 leads into the separation portion 10, is tubular, and extends from an axial position between two end faces 16, 19 of the rotor core 2 beyond a free end 4a of the shaft 4. The fluid-guiding portion 11 consequently extends through the first shaft portion 8 and continues into and through the second shaft portion 9. In addition, the separation element 5 comprises a support portion 12, which is arranged on the fluid-guiding portion 11 between the free end and the separation portion 10 and supports the separation element 5 in the first shaft portion 8 in such a way that a cooling fluid can flow past the support portion 12 through the first shaft portion 8.