  The spatial structure of an ultra-low emittance electron bunch in a plasma
wakefield blowout regime is studied. The full Li\'{e}nard-Wiechert potentials
are considered for mutual inter-particle interactions in the framework of the
equilibrium slice model (ESM). This model uses the quasi-static theory which
allows to solve the Li\'{e}nard-Wiechert potentials without knowledge of the
electrons' history. The equilibrium structure we find is similar to already
observed hexagonal lattices but shows topological defects. Scaling laws for
interparticle distances are obtained from numerical simulations and analytical
estimations.
