This led to the Princeton Large Torus (PLT), which was completed in 1975. This system was successful to the point where it quickly reached the limits of its ohming heating system, the system that passed current through the plasma to heat it. Among the many ideas proposed for further heating, in cooperation with Oak Ridge National Laboratory, PPPL developed the idea of neutral beam injection. This used small particle accelerators to inject fuel atoms directly into the plasma, both heating it and providing fresh fuel.