Particle acceleration at the Sun and in the heliosphere

Energetic particles are accelerated in rich profusion at sites throughout t he heliosphere. They come from solar flares in the low corona, from shock w aves driven outward by coronal mass ejections (CMEs), from planetary magnet ospheres and bow shocks. They come from corotating interaction regions (CIR s) produced by high-speed streams in the solar wind, and from the heliosphe ric termination shock at the outer edge of the heliospheric cavity. We samp le many populations near Earth, but can distinguish them readily by their e lement and isotope abundances, ionization states, energy spectra, angular d istributions and time behavior. Remote spacecraft have probed the spatial d istributions of the particles and examined new sources in situ. Most accele ration sources can be 'seen' only by direct observation of the particles; f ew photons are produced at these sites. Wave-particle interactions are an e ssential feature in acceleration sources and, for shock acceleration, new e vidence of energetic-proton-generated waves has come from abundance variati ons and from local cross-field scattering. Element abundances often tell us the physics of the source plasma itself, prior to acceleration. By compari ng different populations, we learn more about the sources, and about the ph ysics of acceleration and transport, than we can possibly learn from one so urce alone.