The interaction of thermal oxygen or helium ions and ring current protons may produce a wide variety of phenomena in the magnetosphere. These include the production of energetic oxygen ions or energetic helium ions, modification of the bulge region in the afternoon plasmasphere, heating of electrons in the upper ionosphere and production of stable auroral red arcs, precipitation of energetic protons, and precipitation of energetic &agr; particles. Large-amplitude waves generated in the interaction may also lead to wave-wave coupling. The theory developed also suggests that heavier ions such as lithium artifically injected into the ring current to remove ring current protons may be heated substantially in the process. Computations of wave growth have been made for the first time by using measured ring current fluxes and anisotropies.