A rotor for an electric machine includes a heat pipe cooling system. A rotor core has a number of cavities internal to the rotor core. The cavities are surrounded by a wall defined by the rotor core. A magnetic element disposed in the at least one cavity leaving a void in the at least one cavity between the magnetic element and the wall. A heat pipe evaporator is disposed in the void and conforms to the available space, contacting the magnetic element and the wall to remove heat from the rotor core.