  Using numerical simulations we examine colloids with a long-range Coulomb
interaction confined in a two-dimensional trough potential undergoing dynamical
compression. As the depth of the confining well is increased, the colloids move
via elastic distortions interspersed with intermittent bursts or avalanches of
plastic motion. In these avalanches, the colloids rearrange to minimize their
colloid-colloid repulsive interaction energy by adopting an average lattice
constant that is isotropic despite the anisotropic nature of the compression.
The avalanches take the form of shear banding events that decrease or increase
the structural order of the system. At larger compressions, the avalanches are
associated with a reduction of the number of rows of colloids that fit within
the confining potential, and between avalanches the colloids can exhibit
partially crystalline or even smectic ordering. The colloid velocity
distributions during the avalanches have a non-Gaussian form with power law
tails and exponents that are consistent with those found for the velocity
distributions of gliding dislocations. We observe similar behavior when we
subsequently decompress the system, and find a partially hysteretic response
reflecting the irreversibility of the plastic events.
