Ion acceleration in an expanding plasma

We consider ion acceleration when a tenuous plasma expands in a vacuum. It is shown that the ion acceleration is substantially enhanced for electron distributions that are not Maxwellian and are enriched with fast particles. We investigate wave motions in an expanding plasma. The existence of two greatly differing wave types is indicated: front waves and quasi-self-similar waves. The acceleration of ions in a multicomponent plasma is considered. The results of the theory are compared with the experimental data on the acceleration of ions in a plasma produced by intense laser pulses; it is shown that they are in sufficient agreement.