Electron scattering on small-scale electrostatic fields in the shock front

Electron heating and acceleration in collisionless shocks is a long-standing problem.Rapid isotropization of heated electrons cannot be explained solely by the cross-shockpotential. In addition, the macroscopic cross-shock potential prevents efficient reflectionand injection into the diffusive acceleration regime. Recent observations have shown that small-scale electric fields are present in the shock front, together with the large-scalecross-shock potential. These small-scale fields have been found also in the upstream and downstream regions. Electron heating in shocks is produced by the combined action of thelarge- and small-scale fields. The large-scale potential determines the energy transferredto the electrons. The small-scale electrostatic fields scatter electrons. Here we study thescattering of electrons on the typical waveforms, namely solitary bipolar spikes andwavepackets. The main effect is the generation of backstreaming electrons with largepitch angles. It is found that wavepackets are more efficient in electron reflection in theinteraction of electrons both with a single spike and with multiple spikes.