Ion Coulomb explosion of clusters by a Gaussian laser beam

A collisionless model of ion Coulomb explosion of clusters, due to an intense short pulse laser with Gaussian radial intensity distribution, is developed. The laser quickly converts the clusters into plasma balls via tunnel ionization. The free electrons of a cluster execute oscillatory motion with large excursion Δ and partially move out of the cluster. The unbalanced positive charge within the cluster leads to ion Coulomb explosion. The ion energy distribution function due to a single cluster rises monotonically with energy ε up to a cutoff energy εm and vanishes beyond it. εm depends on electron excursion, hence decreases with r. The cumulative ion energy distribution due to all the clusters of the laser channel turns out to be a decreasing function of energy as observed in recent experiments. The ions so produced can generate neutrons with reasonably high yields. The scheme may also find application in tokamak fusion