by large scale electric fields, in pulsars, for instance. However, a somewhat more realistic way to view these particles under most circumstances is as a high energy component of the ionized matter in the universe. Galactic CRs, for example, have roughly the same elemental composition as the interstellar medium at those energies where this property is well measured. They are very likely to have come from the interstellar medium.

Cosmic plasmas are largely “collisionless” in the sense that binary Coulomb collisions play a minor role in dissipation of energy. Instead, dissipation comes from “collective” interactions that depend on fluctuations in charge and currents (i.e., plasma waves or turbulence). These interactions tend to be selective in their efficiency, so that cosmic plasmas are probably rarely fully thermalized. The problem is that they never have the time and they are not really closed systems in the thermodynamic sense. This especially applies to the most energetic charged particles, a point that was also central to our discussions in the previous section. In that sense cosmic rays can be seen as those particles that have so-far escaped being thermalized, but have preferentially extracted energy from a system out of thermodynamic equilibrium. The prototype acceleration 