Numerical solutions of the time-dependent Ginzburg-Landau equations sh
ow a new mechanism for plastic motion of a driven vortex lattice in a
clean superconductor. The mechanism, which involves the creation of a
defect superstructure, is intrinsic to the moving vortex lattice and i
s independent of bulk pinning. Other structural features found in the
solutions include a reorientation of the vortex lattice and a gradual
healing of lattice defects under the influence of a transport current.