Plasma Kinetics

Abstract

In Chapter 7 of ISSI SR-001, Schwartz et al. [1998] explain the basic ideas of analysis by means of plasma kinetics: Liouville mapping and finite gyroradius effects. Liouville mapping can be used to relate features of distribution functions such as heating, anisotropies or beams, to the field variations. It is based on the conservation of phase space density along particle trajectories in collisionless plasmas, and therefore requires that particle trajectories (or at least their initial and final states) can be accurately approximated. This requirement generally relies on invariants of the particle motion such as the energy and adiabatic invariants and some knowledge of the electromagnetic fields along the trajectories. The large gyroradius of energetic ions has the consequence that ions detected at different directions are actually probing conditions at considerable distances around the space- craft. Density gradients then appear as gyrophase anisotropies in the angular distributions. This effect was first employed by Kaufmann and Konradi [1973] to probe the magnetopause. Section 7.5 of Schwartz et al. [1998] explain how it can be used to remotely sense sharp boundaries in ion densities. In particular, see Figures 7.4 and 7.6 in that chapter for a graphical demonstration.

For a historical perspective on these topics, see also the classic paper by Northrop and Teller [1960] on the motion of charged particles in the Earth's magnetic field. In addition, Whipple et al. [1998] present an alternative framework that builds on the underlying concepts, while Whipple et al. [1986] describe extensions to the classic adiabatic theory that apply even in regions of strong gradients.