Pickup ion acceleration by turbulent electric fields in the slow solar wind

Recent spacecraft observations reveal that energetic tails in ion spectra a re present continually in the slow low-latitude solar wind, even in the abs ence of nearby shocks. To explain this phenomenon we take into account grow ing evidence that MHD turbulence in the solar wind has a strong two-dimensi onal (2D) component. 2D MHD turbulence simulations exhibit large-scale fiel d-aligned electric field fluctuations which are also observable in the sola r wind. We explore pickup ion propagation and acceleration between the Sun and Earth with a newly developed kinetic numerical model which includes a r andom distribution of large-scale field-aligned electric field fluctuations consistent with observations in the low-latitude solar wind. The model is found to qualitatively reproduce the accelerated interstellar pickup He+ sp ectra observed at Earth. Like the observations, the simulated accelerated " tail" is approximately a power law f (v) proportional to v(-4.5) until it r eaches particle speeds about ten times the solar wind speed where a rollove r occurs.