Ion acceleration by hot electrons in micro-clusters

Neutron yield, observed in experiments with laser-irradiated deuterium clusters [1], is associated with fast multi-keV ions. Such ions are produced by large clusters that contain a population of stochastically heated electrons [2]. Our work deals with a first-principle theory of ion acceleration to multi-keV energies. We present a semi-analytical description for collisionless expansion of a fully ionized cluster with a two-component electron distribution function. The problem is solved for a ``water-bag'' distribution function of the hot electrons with self-consistent treatment of ion acceleration and electron cooling. The solution involves a cold core of the cluster, a thin double layer at the cluster edge, and a quasineutral flow with a rarefaction wave. The asymptotic energy spectrum of the accelerated ions contains a substantial number of particles with energies greater than the maximum electron energy. \newline \newline [1] T. Ditmire et al., Nature \textbf{398}, 489 (1999). \newline [2] B. N. Breizman, A. V. Arefiev, and M. V. Fomyts'kyi, Phys. Plasmas \textbf{12}, 56706 (2005).