Energetic particles in plasma astrophysics

Cosmic ray and gamma-ray astrophysics provides an arena where concepts drawn from many branches of plasma physics can assist in answering questions of fundamental-indeed cosmological-significance. In recent years, striking advances have been made in the quality and resolution of the data available in this field. The present generation of cosmic ray detection arrays and space-based x-ray and gamma-ray observatories, coupled to measurements in other wavebands, are yielding information which invites detailed quantitative interpretation in terms of plasma processes. In parallel with these developments, a systematic picture of the behaviour of energetic particle populations in magnetically confined plasmas has emerged from the deuterium-tritium experimental campaigns on JET and TFTR, and the acceleration of electrons to highly relativistic energies has been demonstrated in laser-plasma interaction experiments. This review is written primarily to assist the deployment in energetic particle astrophysics of methodologies used for studying high-temperature fusion plasmas: three topics are examined. What are the major plasma-oriented questions in energetic particle astrophysics? What solutions have been proposed? How can plasma physics assist in deepening, strengthening and extending current understanding?