  Impulsive solar energetic electrons are often observed in the interplanetary
space near the Earth and have an attractive diagnostic potential for poorly
understood solar flare acceleration processes. We investigate the transport of
solar flare energetic electrons in the heliospheric plasma to understand the
role of transport to the observed onset and spectral properties of the
impulsive solar electron events. The propagation of energetic electrons in
solar wind plasma is simulated from the acceleration region at the Sun to the
Earth, taking into account self-consistent generation and absorption of
electrostatic electron plasma (Langmuir) waves, effects of non-uniform plasma,
collisions and Landau damping. The simulations suggest that the beam-driven
plasma turbulence and the effects of solar wind density inhomogeneity play a
crucial role and lead to the appearance of a) spectral break for a single
power-law injected electron spectrum, with the spectrum flatter below the
break, b) apparent early onset of low-energy electron injection, c) the
apparent late maximum of low-energy electron injection. We show that the
observed onsets, spectral flattening at low energies, and formation of a break
energy at tens of keV is the direct manifestation of wave-particle interactions
in non-uniform plasma of a single accelerated electron population with an
initial power-law spectrum.
