  The impulsive phase of a solar flare marks the epoch of rapid conversion of
energy stored in the pre-flare coronal magnetic field. Hard X-ray observations
imply that a substantial fraction of flare energy released during the impulsive
phase is converted to the kinetic energy of mildly relativistic electrons
(10-100 keV). The liberation of the magnetic free energy can occur as the
coronal magnetic field reconfigures and relaxes following reconnection. We
investigate a scenario in which products of the reconfiguration - large-scale
Alfven wave pulses - transport the energy and magnetic-field changes rapidly
through the corona to the lower atmosphere. This offers two possibilities for
electron acceleration. Firstly, in a coronal plasma with beta < m_e/m_p, the
waves propagate as inertial Alfven waves. In the presence of strong spatial
gradients, these generate field-aligned electric fields that can accelerate
electrons to energies on the order of 10 keV and above, including by repeated
interactions between electrons and wavefronts. Secondly, when they reflect and
mode-convert in the chromosphere, a cascade to high wavenumbers may develop.
This will also accelerate electrons by turbulence, in a medium with a locally
high electron number density. This concept, which bridges MHD-based and
particle-based views of a flare, provides an interpretation of the
recently-observed rapid variations of the line-of-sight component of the
photospheric magnetic field across the flare impulsive phase, and offers
solutions to some perplexing flare problems, such as the flare "number problem"
of finding and resupplying sufficient electrons to explain the impulsive-phase
hard X-ray emission.
