Abstract: A rotor assembly end turn cooling system and method in which cooling fluid is introduced at both ends of each cooling fluid passageway and at various points therebetween and spent cooling fluid is exhausted through exhaust openings disposed at various points between the ends of each cooling fluid passageway, including near the end turn corners. Multi-layered bore baffle shells and/or helical exhaust ducts having multiple channels control the flow of cooling fluid through the passageways and into axial rotor slots for expulsion into the rotor-stator gap. Each duct or channel may increase in cross-sectional area in the flow direction to maintain constant fluid flow velocity in the duct or channel. Improved end turn cooling and reduced cooling fluid temperatures maintain more consistent temperatures in the end turns and reduce the maximum hot-spot temperature to provide greater generator power densities and longer rotor coil insulation life.