In one embodiment, a generator or an alternating current (AC) motor includes a stator and a rotor. The rotor is configured to rotate at least partially within the stator or around the stator and is separated from the stator by a gap having a partial vacuum. The rotor includes a shaft configured to permit a flow of coolant and a plurality of microchannels formed within the rotor. The microchannels are fluidly coupled to the shaft and are configured to permit the coolant to pass from the shaft through at least a portion of the rotor in order to provide cooling for the rotor.