Expansion of a slab of a three-component plasma with negative ions into vacuum
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MA DYNAMICS
Expansion of a Slab of a ThreeComponent Plasma with Negative Ions into Vacuum Yu. V. Medvedev Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya ul. 13/19, Moscow, 125412 Russia Received March 12, 2009; in final form, October 26, 2009
Abstract—The expansion of a slab of a threecomponent collisionless plasma with negative ions into vacuum is studied by particleincell numerical simulations. It is found that, when the ion temperatures are low in comparison with the electron temperature, the expansion process goes through several characteristic stages. The breaking phenomenon, the onset of multistream motion, and the development of instability are described. DOI: 10.1134/S1063780X10060061
1. INTRODUCTION The problem of the expansion of a collisionless plasma into vacuum was first considered by Gurevich et al. [1], who showed that, in the quasineutral approx imation, the ion motion is described by a selfsimilar kinetic equation and also presented solutions to this equation. The phenomenon of substantial ion acceler ation revealed in that paper initiated the development of a new direction in the methods for producing accel erated particle beams, and this circumstance alone is enough to demonstrate how important it is to investi gate problems of this kind. Research efforts were focused on the expansion into vacuum of a plasma with positive ions. At the same time, the expansion process can also play an important and even a governing role in the creation and maintenance of a plasma consisting of electrons and positive and negative ions. A threecomponent collisionless plasma with negative ions is widely used as a physical object with unusual wave properties [2– 5]. In such a plasma, there can exist various nonlinear structures, in particular, solitons and both rarefaction and compression shock waves [6–11]. It is remarkable that, in a threecomponent plasma with negative ions, complex nonlinear structures can arise even in situa tions in which the flow in a twocomponent plasma is monotonic. Of course, in order to correctly interpret the observed nonlinear motions, it is necessary to take into account the characteristic features of the flow driven by the plasma expansion process. Note also that the problem under consideration can give initial insight into the processes that can occur during the expansion into vacuum of a more complex plasma—that with dust grains. Many non linear phenomena occurring even in a threecompo nent plasma with negative ions are rather difficult to study, not to mention those occurring in a dusty
plasma, with its wide variety of processes. This is why, in one of the first papers on the subject, Luo and Yu [12] solved the problem by assuming that all the dust grains have the same size, mass, and charge; in other words, they described the grains in the same manner as negative ions. In one of their papers [13], they investi gated the expansion into vacuum of a plasma consist ing of electrons, positive ions, and two species of dust grains. In late
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