THE PROPAGATION OF ENERGETIC PARTICLES IN FINITE TEMPERATURE ASTROPHYSICAL PLASMAS.

Abstract

Solutions to the dispersion relation for waves propagating parallel to the static magnetic field in a plasma of arbitrary β are obtained. (β is the ratio of thermal to magnetic pressure.) Resonant scattering by these waves is evaluated. It is found that the magnetostatic approximation, used extensively in the past, breaks down for particles with pitch angles near 90°, and one must consider the more complicated process of particle scattering in electromagnetic turbulence. Many aspects of particle propagation in a finite temperature plasma can be discussed without assuming magnetostatic turbulence. This is accomplished by using a graphical method to obtain the solutions of the resonance condition. Results show that in a high β plasma, wave damping causes a gap, or hole, in μ-space where the resonant particle scattering rate is severely depressed. It is found that only high energy (γ ≥10⁵) electrons can be trapped within a typical supernova remnant. When the notion of electromagnetic resonance is applied to particle propagation in the interplanetary β ≤ 1) plasma, it is found that significant modifications to the conventional scattering picture must be made. It is found that a resonance gap exists which is similar to the one in a high β plasma. For electrons, this gap provides a natural explanation for scatter-free events. Theory predicts that these events should occur for kinetic energies T ≤ 300 keV while observations indicate that the majority have T ≤ 500 keV. For protons and energetic electrons, the scattering mean free path is critically dependent on the non-resonant scattering rate for particles within the gap. This fact provides a way to resolve the well known discrepancy between the theoretical and observational values for the mean free path, λ.