  The expansion of a radial blast shell into an ambient plasma is modeled with
a particle-in-cell (PIC) simulation. The unmagnetized plasma consists of
electrons and protons. The formation and evolution of an electrostatic shock is
observed, which is trailed by ion-acoustic solitary waves that grow on the beam
of the blast shell ions in the post-shock plasma. In spite of the initially
radially symmetric outflow, the solitary waves become twisted and entangled
and, hence, they break the radial symmetry of the flow. The waves and their
interaction with the shocked ambient ions slows down the blast shell protons
and brings the post-shock plasma closer to an equilibrium.
