M. A. Lee University of New Hampshire, Durham NH, USA
The populations of energetic particles observed in the heliosphere by ACE include galactic cosmic rays, the anomalous cosmic ray component, solar energetic particles, and shock-associated enhancements. Interstellar pickup ions and the solar wind itself, while not energetic in the usual sense, are substantially heated and/or accelerated and provide the source particles for the heliospheric populations. The general characteristics of these particle populations are first reviewed briefly. The basic acceleration and injection mechanisms responsible for accelerating each population are described, and, where competing mechanisms have been proposed, the merits of each are reviewed. Open questions and puzzles concerning the acceleration and transport of these populations are highlighted; the potential for ACE observations to answer these questions is emphasized. The talk ends with a preview of the ACE-2000 Symposium including anticipated new observations and challenges to theory.