Oblique propagation of ion-acoustic solitons in a magnetized low-β plasma consisting of warm positive and negative ion species along with hot electrons is studied. Using the reductive perturbation method, a KdV equation is derived for the system, which admits an obliquely propagating soliton solution. It is found that if the ions have finite temperatures then there exist two types of modes, namely slow and fast ion-acoustic modes. The parameter determining the nature of soliton (i.e. whether the system will support compressive or rarefactive solitons) is different for slow and fast modes. For the slow mode the parameter is the relative temperature of the two ion species, whereas for the fast mode it is the relative concentraion of the two ion species. For the fast mode it is found that there is a critical value of the negative-ion concentration below which only compressive solitons exist and above which rarefactive solitons exist. To discuss the soliton solution at the critical concentration, a modified KdV equation is derived. It is found that at the critical concentration of negative ions compressive and rarefactive solitons co-exist. The effects of temperature of different ion species, angle of obliqueness and magnetization on the characteristics of the solitons are discussed in detail.
Propagation of ion-acoustic solitons in a plasma consisting of warm positive and negative ion species with different masses, concentrations, and charge states, along with hot electrons, is studied. It is found that the finite temperatures of two ion species give rise to two types of modes, i.e., a slow ion-acoustic mode and a fast ion-acoustic mode. For all values of negative ion concentration, the slow wave mode supports compressive ͑rarefactive͒ solitons, when the negative ion species has a higher ͑lower͒ temperature than the positive ion species. The fast wave mode supports compressive solitons for low concentration of negative ions. At the critical concentration of negative ions both compressive and rarefactive modified Korteweg-de Vries solitons coexist. Above this critical concentration the system supports rarefactive solitons. The dependence of the critical concentration on the temperatures of two ion species is also discussed.
The stability of oblique modulation of ion-acoustic waves in a collisionless plasma consisting of two cold-ion species with different masses, concentrations, and charge states, and hot isothermal electrons is studied. Using the Krylov–Bogoliubov–Mitropolosky (KBM) perturbation technique, a nonlinear Schrödinger equation governing the slow modulation of the wave amplitude, is derived for the system. It is found that the presence of second-ion species significantly changes the instability domain in the k-φ plane. The effect of charge state, concentration, and mass of second-ion species on the modulational instability is discussed in detail. The predictions of the theory are found to be in good agreement with the experimental observations.
Propagation of ion-acoustic double layers has been studied in plasma consisting of warm positive- and negative-ion species with different masses, concentrations, and charge states along with electrons with two-electron temperature distributions. It is found that there exist two critical concentrations of negative ions, alpha(R) and alpha(Q). One of them (alpha(R)) generally decides the existence of the double layer, whereas the other one (alpha(Q)) decides the nature of the double layer. It is found that the system supports ion-acoustic double layers only when the negative-ion concentration (alpha) is greater than the critical concentration alpha(R). It is also found that below the critical concentration alpha(Q), compressive double layers exist and above it rarefactive double layers exist. For some values of cold-electron concentrations (mu) it is found that if the temperature of the negative-ion species is higher than the positive-ion species, then the system supports compressive double layers for all values of alpha lying in the range 0
Using the KBM perturbation technique, the stability of oblique modulation of ion-acoustic waves in a two-ion plasma is studied. It is found that the presence of a small amount of lighter ion impurities significantly changes the instability domain in the ω-φ plane. The effect of the concentration and mass of impurity ions on the modulational instability is discussed in detail. The threshold amplitude for instability and nonlinear frequency shift of the wave are also calculated. The predictions of the theory are found to be in good agreement with the experimental observations.
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