  We present the results of direct simulation of the expansionof a
two-component ultracold plasmafor various numbers of particles, densities, and
electron temperatures. A description of the expansionprocess common to all
plasma parameters is given. After the escape of fast electrons from the
plasmacloud, the excess positive charge is localized at the outer boundary, in
a narrow layer. This layerhas a characteristic front shape with a sharp drop in
the charge concentration. The charged layerretains the remaining electrons
during the entire expansion process. As the plasma expands, thespeed of
movement of the charged layer becomes constant and significantly exceeds the
sonic speedof ions. In addition, the dependence of the radial velocity of ions
on the radius acquires a self-similarcharacter long before the final stage of
expansion. On the basis of the calculation results, equationsand self-similar
solutions are obtained. General dependences on plasma parameters are
determined,which are compared with experimental data.
