Ion front and ablation in a freely expanding two-ion, two-temperature, noncollisional plasma

The equations for the free expansion of a two-ion, two-temperature, noncollisional, isothermal, and quasineutral plasma are derived and solved using a self-similar technique. The hydrodynamic variables are determined by four independent parameters, viz., α, the relative charge to mass ratio of the two ions; N10, the initial concentration of the main ion; tau, the temperature ratio of the hot and cold electrons; and rho, the initial concentration ratio of the cold and hot electrons. The formation of an ion front in the numerically dominant species is predicted for the first time even under the quasineutral and isothermal assumptions. A necessary condition for the breakdown of the self-similar solution is derived. The location of the ion front and the point where the solution breaks down are tabulated as a function of the four parameters and the results are discussed. The expression for the normalized ion current, taking into account the flux limitation under the free-streaming limit, is derived. The expressions for the mass, momentum, and energy ablation are also derived and the relevant data are discussed with reference to laser--plasma interaction