Shock drift acceleration of electrons: A parametric study

Abstract

Spikes of energetic (1–100 keV) electrons have been observed at the nearly perpendicular Earth's bow shock and at traveling interplanetary shocks and have been explained as solar wind electrons accelerated by the shock drift mechanism. We present spectral and angular distributions of the accelerated electrons using the theory of shock drift acceleration at curved shocks. The influence of various shock parameters on these distributions is extensively discussed here. The theoretical fluxes of accelerated electrons are highly anisotropic, and their spectra cannot be fitted by a power law. The spectra strongly depends on the location near the shock, and they are harder for upstream electrons: the highest fluxes can be found in the regions of the shock with θBn ≈ 86°–88°. The fluxes of reflected electrons increase with decreasing shock curvature or shock thickness, while fluxes of transmitted electrons do not depend significantly on these parameters. The magnetic field profile shapes through the shock have no large effect on the acceleration. A higher upstream plasma velocity (Mach number) results in larger electron fluxes. These basic properties of electron distributions are then qualitatively compared with observational facts. These comparisons lead us to the conclusion that the shock drift acceleration is strongly modified by some additional processes, which could be pitch angle scattering of electrons in the shock layer, or spatial/temporal changes of the shock front.