Accumulation of accelerated electrons in coronal loops and time delays of solar flare nonthermal emission

The mechanisms by which accelerated electrons accumulate in flare loops with regard to the observed time delays between peaks of prolonged (a parts per thousand << 1 s) hard X-ray pulses with different energies are considered. The focus is on an analysis of electron pitch-angle scattering by background plasma particles and/or turbulent pulsations in extreme cases of frequent and rare collisions. It was shown that it is difficult to explain the origination of time delays in the scope of a diffusion model when the electron free path length (l) in the corona is smaller than the flare loop length (L). The accumulation of energetic particles in loops at l > L is related to a trap-plus-precipitation model in which the regime of weak pitch angle diffusion of trapped electrons in the loss cone predominates.