In this chapter, we review the basic principles and characteristics of shock acceleration. After a brief description of the pertinent kinetic scales at shocks and a discussion of heating versus acceleration, we outline the different mechanisms that contribute to accelerating charged particles at shocks. The main emphasis throughout this chapter is on ions, and more importantly, on protons. Acceleration of other ion species or electrons is mentioned in passing and when contrasting interesting differences. Also, we restrict the discussion to the collisionless and non-relativistic shocks that occur in the heliosphere. Finally, we describe particle acceleration at interplanetary shocks and at the Earth's bow shock in greater detail, and discuss the differences between these two. Throughout the chapter, fundamental, underlying principles, historic results, and current research interests are brought together as much as possible.

Introduction

More than half a century ago, energetic particle events detected at Earth with energies into the GeV range were for the first time unambiguously associated with activity in the solar corona. While this link was established based on concomitant solar flare observations, in the 1970s and early 1980s evidence accumulated that so-called “gradual” solar energetic particle (SEP) events are actually caused by acceleration at coronal and interplanetary (IP) shocks (Sarris and Van Allen, 1974; Cliver et al., 1982; Mason et al., 1984). The 1970s and early 1980s also saw a rapid development in the theory of charged particle acceleration at shocks, and the realization that virtually all heliospheric shocks carry with them energetic particle populations.