[en] A rotor of an electrical machine has a superconducting winding which is connected to a heat exchanger in the cavity of the rotor. The heat exchanger feeds coolant to and withdraws coolant from the rotor. A thermal/electromagnetic shield, radially spaced from the superconducting winding, is connected with a ranque vortex tube disposed in the cavity of the rotor. The rotor also has power leads having cooling ducts connected to the ranque vortex tube and to the coolant discharge line. In addition, the rotor has two reducer portions adjacent the superconducting winding, arranged in series along the axis of the rotor on either side of the superconducting winding and each having a cooling duct located in close proximity to the superconducting winding and connected to ranque vortex tube. The outlets of the cooling ducts of the reducer portions are connected with the coolant discharge line. The ranque vortex tube is connected with the coolant supply line, while the outlet of the cooling duct of the thermal/electromagnetic shield is connected to the cooling duct of the reducer portions