Particle acceleration at interplanetary shocks

This paper briefly reviews proton acceleration at interplanetary shocks. This is key to describing the acceleration of heavy ions at interplanetary shocks because wave excitation-and hence particle scattering-at oblique shocks is controlled by the protons and not the heavy ions. Heavy ions behave as test particles, and their acceleration characteristics are controlled by the properties of proton-excited turbulence. As a result, the resonance condition for heavy ions introduces distinctly different signatures in abundance, spectra, and intensity profiles, depending on ion mass and charge. Self-consistent models of heavy-ion acceleration and the resulting fractionation are discussed. This includes discussion of the injection problem and the acceleration characteristics of quasi-parallel and quasi-perpendicular shocks.