Multi-ion plasma expansion in the presence of suprathermal electrons

The self similar expansion of a two-ion plasma is investigated via a multi-fluid model. Our aim is to elucidate the effect of secondary ions on the plasma expansion front, in combination with energetic (suprathermal) electrons in the background. Considering an analytically tractable situation (namely, assuming secondary ions to represent a minority population), and adopting a kappa-type distribution function for the suprathermal electrons, it is shown that energetic electron contribute to acceleration of the expansion front and to an increase in the associated electric field. Introduction. Plasma expansion into vacuum has received growing interest in recent years, in particular due to its relevance with experiments on ultraintense laser pulse interaction with solid targets [1], and with applications of high energy ion beams, e.g. for ion acceleration [2] and laser-assisted fast ignition scenaria for fusion [3] among others. Plasma expansion mechanisms are also involved in experimental low-temperature plasmas [4] and in plasmas for medical applications (e.g. cancer therapy) [5]. Recent studies have considered the role of secondary ions (rather than electrons) in ultrafast collisional plasma heating by electrostatic shocks [6]. Since multi-ion configurations appear to be ubiquitous in laser-plasm interactions [7], this is expected to be an area of growing interest in the years to come. Furthermore, the generation of energetic (suprathermal) electrons during laser-plasma interactions is a known phenomenon [8]; its effect on expanding plasmas has been investigated in simple electron-ion configurations [9], but never in multispecies plasmas, to the best of our knowledge. Inspired by an earlier study of two-ion expanding plasma [10], this paper is dedicated to an investigation of the dynamics of expanding plasma in a two-ion configuration, in the presence of energetic (suprathermal) electrons. Theoretical model.We consider a planar plasma slab consisting of electrons (absolute charge e, mass me) and two different (positive) ion populations. The two ion species are characterized by their respective mass m j, charge q j = z je and temperature Tj,0, as well as their equilibrium density n j,0, respectively (for j = 1,2). The plasma is assumed to be quasineutral, hence, the electron number density inside the slab equals ne,0 = ∑z jn j,0 at equilibrium. 43 EPS Conference on Plasma Physics P4.082