Particle acceleration in the sun and heliosphere

Our current understanding of the acceleration of energetic charged particles of heliospheric origin is reviewed. This paper outlines the key points, topics, and open issues that were discussed in the tutorial talk on energetic particles in the Sun and heliosphere. Because of the broad scope of this topic, much of the review focused on solar energetic particles. Moreover, while a few acceleration mechanisms were discussed, much of the emphasis was placed on the physics of diffusive shock acceleration. This mechanism naturally leads to power-law energy spectra which are commonly observed in the distributions of energetic particles in space plasmas. The theme of the tutorial was that the energy spectrum of most solar-energetic particle events, as well as other energetic nuclei of heliospheric origin, and galactic cosmic rays, share one common characteristic: they are all power laws below a characteristic energy. Moreover, the spectral index does not vary much from one event to the next. Any successful acceleration mechanism must be able to produce this feature naturally. Currently, only diffusive shock acceleration does this.