  Non-relativistic collisionless shock waves are widespread in space and
astrophysical plasmas and are known as efficient particle accelerators.
However, our understanding of collisionless shocks, including their structure
and the mechanisms whereby they accelerate particles remains incomplete. We
present here the results of numerical modeling of an ion-acoustic collisionless
shock based on one-dimensional (1D) kinetic approximation both for electrons
and ions with a real mass ratio. Special emphasis is made on the
shock-reflected ions as the main driver of shock dissipation. The reflection
efficiency, velocity distribution of reflected particles and the shock
electrostatic structure are studied in terms of the shock parameters.
Applications to particle acceleration in geophysical and astrophysical shocks
are discussed.
