The time evolution of the distribution function of newborn ions in the solar wind is investigated within the context of a quasi-linear theory in which the level of intrinsic turbulence is assumed to be moderate and known. The initial distribution is taken to be a ring beam, which is approximated by delta functions in pitch angle and velocity, and it is assumed that the ions are created at a constant rate with a similar distribution. The long-time asymptotic form of the distribution is obtained. This distribution is a mixture of ions created recently and ions generated throughout the entire process. The results obtained in the present analysis are found to be in good agreement with recent satellite observations. The time asymptotic distribution is also found to be unstable to low-frequency hydromagnetic waves propagating parallel to the ambient magnetic field. ¿ American Geophysical Union 1989