[en] The distortion of the background-ion distribution function produced by Coulombic large-energy-transfer collisions with beam-injected ions, and the effects of this distortion in fusion experiments and reactors are examined. A binary collision operator describing the superthermal background-ion Coulombic interaction has been developed which explicitly includes the discrete nature of the large-energy-transfer collisions. The effects neglected by the cold-target assumption and the small-energy-transfer approximation are regained in this analysis. This mechanism is found to 'broaden' the background-ion Maxwellian in energy. This broadening of the Maxwellian can substantially enhance the fusion energy production for a given expenditure of neutral-beam-heating energy during the startup heating phase. (author)