Supersonic and near-sonic solitary ion-acoustic waves in magnetized plasma
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Supersonic and NearSonic Solitary IonAcoustic Waves in Magnetized Plasma V. V. Prudskikh Research Institute of Physics, Southern Federal University, pr. Stachki 194, RostovonDon, 344090 Russia Received April 9, 2010
Abstract—The propagation of largeamplitude solitary ionacoustic waves in magnetized plasma is analyzed. The problem is solved without assuming plasma quasineutrality within the pulse, and the wave potential is described by Poisson’s equation. Solutions in the form of supersonic and nearsonic solitary waves propagat ing obliquely to the magnetic field are found. The pulses have several peaks and exist for a discrete set of the wave parameters. The amplitude and oscillation frequency of a solitary wave are determined as functions of the Mach number and the propagation angle with respect to the magnetic field. DOI: 10.1134/S1063780X10110085
1. INTRODUCTION The existence of ionacoustic solitons propagating obliquely to the external magnetic field was predicted in [1–4]. Such solitons have the shape of a hump in the plasma density profile and exist for cos θ < V/ c s < 1, where θ is the angle between the wave propagation direction and the magnetic field B 0 , cs = (Te/ mi)1/ 2 is the ion sound speed, and V is the wave propagation velocity. The dispersion relation for a linear lowfre quency ionacoustic mode in magnetized plasma has the form
ω=
(1 +
k zc s 2 2 k λD +
k⊥2ρi2)1/ 2
.
(1)
Here, λ D = ( Te/ 4 πe 2n0)1/ 2 is the electron Debye length, ρi = cs/ ωci is the ion gyroradius, ωci is the ion gyrofrequency, Te is the electron temperature, and n0 is the unperturbed plasma density. If the condition ω pi Ⰷ ωci (where ω pi is the ion plasma frequency) is satisfied and the wave propagation direction is not quasilongitudinal (k⊥ ≤ k ), then the wave dispersion is determined by the ion gyroradius. In this case, the effect of charge separation within the pulse can be ignored and the plasma quasineutrality condition is satisfied. There were a large number of studies in which the properties of nonlinear ionacoustic waves propagating obliquely to the external magnetic field in electron–ion plasma [5, 6], plasma with several ion species [7, 8], plasma with twotemperature electrons [9, 10], and dusty plasma [11–16] were investigated. If the condition ω pi Ⰷ ωci is not satisfied or the wave propagation direction is quasilongitudinal (k⊥ Ⰶ k ), then the effect of charge separation on the
properties of ionacoustic waves should be taken into account. Modified solutions describing nonlinear waves with allowance for charge separation were obtained in [6], where the existence of negative ion acoustic solitons in a twocomponent electron–ion plasma was reported. Note that such solitons are absent when charge separation is not taken into account. Choi et al. [13] studied the propagation of oblique ionacoustic waves in dusty plasma. It was found that the soliton can have the shape of a well in the plasma density profile and that the density of the negatively charged dust background requ
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