Ion acceleration and plasma jet formation in the interaction of an intense laser beam normally incident on an overdense plasma: a Vlasov code simulation

Abstract

We use an Eulerian Vlasov code for the numerical solution of the one-dimensional relativistic Vlasov?Maxwell set of equations to study the acceleration of ions during the interaction of a high-intensity circularly polarized laser beam normally incident on an overdense plasma target. Both electrons and ions are treated with a kinetic equation. We consider the case when the laser free space wavelength ? 0 is greater than the scale length of the jump in the plasma density at the target plasma edge Ledge (? 0 Ledge). The laser beam intensity is a Gaussian-shaped pulse. We consider a density such that n/ncr=25 (ncr is the critical density). The ponderomotive pressure due to the incident high-intensity laser radiation pushes the electrons at the target plasma surface, producing a sharp density gradient, which gives rise to a charge separation. The resulting electric field accelerates the ions. Two cases are considered, namely the case of a relatively thin target (about five skin depth) and the case of a much larger target. The evolution of the charge separation, the associated electric field and the formation of a neutral plasma jet ejected toward the rear side of the target differ in the two cases considered. In the case of a thin target, we observe the ion population accelerated to higher velocities. The absence of noise in the Eulerian Vlasov code allows a detailed representation of the phase-space structures of the distribution functions associated with the two cases considered, which shows substantial differences to be discussed in this paper.