Nonlinear Propagation Of Ion-acoustic Waves Research Articles

Oblique electrostatic excitations in a magnetized plasma in the presence of excess superthermal electrons

The nonlinear propagation of ion-acoustic waves is considered in a magnetized plasma, composed of kappa distributed electrons and an inertial ion fluid. The fluid-dynamical system of equations governing the dynamics of ion-acoustic waves is reduced to a pseudoenergy-balance equation. The properties of arbitrary amplitude, obliquely propagating ion-acoustic solitary waves are thus investigated via a mechanical-motion analog (Sagdeev potential) approach. The presence of excess superthermal electrons is shown to influence the nature of magnetized ion-acoustic solitons. The influence on the soliton characteristics of relevant physical parameters such as obliqueness (the angle between soliton propagation direction and magnetic field), the electron deviation from a Maxwellian (“superthermality”) and the soliton speed is investigated.

Dynamics of modulationally unstable ion-acoustic wavepackets in plasmas with negative ions

AbstractIn this paper we study the propagation of nonlinear ion-acoustic waves in plasmas with negative ions. The Gardner equation governing these waves in plasmas with the negative ion concentration close to critical is derived. The weakly nonlinear theory of modulational instability based on the use of the nonlinear Schrödinger equation is discussed. The investigation of the nonlinear dynamics of modulationally unstable quasi-harmonic wavepackets is carried out by the numerical solution of the Gardner equation. The results are compared with the predictions of the weakly nonlinear theory.

Nonlinear propagation of ion-acoustic waves in electron-positron-ion plasma with trapped electrons

A theoretical investigation has been made for ion-acoustic waves in an unmagnetized electron-positron-ion plasma. A more realistic situation in which plasma consists of a negatively charged ion fluid, free positrons, and trapped as well as free electrons is considered. The properties of stationary structures are studied by the reductive perturbation method, which is valid for small but finite amplitude limit, and by pseudopotential approach, which is valid for large amplitude. With an appropriate modified form of the electron number density, two new equations for the ion dynamics have been found. When deviations from isothermality are finite, the modified Korteweg-deVries equation has been found, and for the case that deviations from isothermality are small, calculations lead to a generalized Korteweg-deVries equation. It is shown from both weakly and highly nonlinear analysis that the presence of the positrons may allow solitary waves to exist. It is found that the effect of the positron density changes the maximum value of the amplitude and M (Mach number) for which solitary waves can exist. The present theory is applicable to analyze arbitrary amplitude ion-acoustic waves associated with positrons which may occur in space plasma.

Nonlinear propagation of ion-acoustic waves and low-frequency electrostatic modes in a dusty plasma

Nonlinear propagation of ion-acoustic waves and low-frequency electrostatic modes in a dusty plasma is investigated. The evolution equations of these modes are developed and solved analytically. It is found that for small grain charge usual ion-acoustic solitons may exist in a dusty plasma, but increasing grain charge destroys them and finally they may disappear. The low-frequency electrostatic mode may be localized, forming solitons, which may act as centres of wave scattering in a dusty plasma.

Cylindrical and Spherical Solitons at the Critical Density of Negative Ions in a Generalised Multicomponent Plasma

Propagation of nonlinear ion-acoustic waves in generalised multicomponent plasmas bounded by cylindrical and spherical geometries is investigated. At the critical density of negative ions where the nonlinearity of the Korteweg-deVries (K-dV) equation vanishes, the ion-acoustic solitary wave is described by a modified K-dV (mK-dV) equation. It is also emphasised that near the critical density neither the K-dV nor mK-dV equation is sufficient to describe fully the ion-acoustic waves and thus there is a need to derive a further mK-dV (fmK-dV) equation in the vicinity of this critical density. Furthermore, the amplitude variations of the K-dV and mK-dV solitons depending on the limitations of geometrical effects are also discussed, emphasising that the results could be of interest for diagnosing the soliton properties of laboratory plasmas.

負イオンを含む多成分プラズマ中の非線形イオン音波

Propagation of nonlinear ion-acoustic waves in a three-component plasma which consists of electrons and positive and negative ions have been investigated theoretically and experimentally. The Korteweg-de Vries (K-dV) equation is obtained by the reductive perturbation of the plasma taking the ion temperature into consideration. The dispersion term of the K-dV equation is positive for the concentration r of the negative ion considered here. On the other hand, the coefficient of the nonlinear term becomes negative at a critical concentration rc which depends on the mass ratio of the negative to positive ions and the temperature ratio of electrons to ions. Therefore, positive (electric potential), compressive (positive ion and electron density) solitons can exist when 0 rc. When r=rc, the nonlinear term in the K-dV equation disappear so that a higher-order term should be considered, which results in the modified K-dV equation. The modified K-dV equation has also soliton solutions which are irrespective of the sign, i.e., both positive and negative solitons coexist. The K-dV and the modified equations are obtained under the assumption that the amplitude is small. When the amplitude is large, original fluid equations are integrated numerically. The result is that when rc<r<rm, positive solitary waves exist if the amplitude is larger than a threshold. Experiments were carried out in a multi-dipole double-plasma device. The inner diameter of the device is 40cm and its total length is 90cm. The device is separated into a driver and a target section with an electrically floating mesh grid. The chamber was evacuated to 1×10-6Torr with a turbo-molecular pump. Argon and sulfur hexafluoride were introduced into the chamber under continuous pumping. Plasma parameters measured with a probe and a retarding energy analyzer were the electron density=108-109cm-3, the electron temperature=0.6-1eV and the ion temperature=0.05-0.1eV. Experimental results are compared with the theoretical results described above.

Effect of higher-order nonlinearity on propagation of nonlinear ion-acoustic waves in a collisionless plasma consisting of negative ions

The combined effects of negative ions and higher-order nonlinearity on ionacoustic solitons are studied using the reductive perturbation method. The basic set of fluid equations for a plasma consisting of negative cold ions, positive cold ions and hot electrons (non-isothermal and isothermal) reduces to the modified Korteweg-de Vries equation and the Korteweg-de Vries equation for the first-order potential, and to the linear inhomogeneous equation for the second-order potential. Stationary solutions of the coupled equations are obtained in the case of negative ions, retaining terms up to the third order in the usual reductive perturbation method.

Modified Korteweg—de Vries ion-acoustic solitons in a plasma

Propagation of nonlinear ion-acoustic waves in a multi-component plasma with negative ions is investigated experimentally. At a critical concentration of negative ions, both compressive and rarefactive solitons are observed. The velocities and widths of the solitons are measured and compared with the soliton solutions of the modified Korteweg–de Vries equation and of the pseudopotential method. The modified Korteweg–de Vries equation is solved numerically to investigate overtaking collisions of a positive and a negative soliton. Fluid equations together with Poisson's equation are numerically integrated to simulate their head-on collisions.

Ion-acoustic shock waves in multi-electron temperature collisional plasma

The nonlinear propagation of ion-acoustic waves in a collision-dominated double electron temperature plasma is considered. Accounting for the ion viscosity and the ion heat conductivity, it is shown by means of two-warm fluid equations that the nonlinear evolution of the ion-acoustic waves is governed by the Korteweg—de Vries—Burgers equation. Stationary shock solution of the KdV—Burgers equation is presented.

Effect of magnetic field on propagation of nonlinear ion-acoustic wave

The Korteweg–de Vries equations describing the propagation of slow and fast nonlinear ion-acoustic waves in a magnetic field are derived by using a perturbation method. The effect of the direction of propagation on the amplitude and width of the solitary solutions are discussed.

Two-dimensional stability of ion-acoustic solitons

Two dimensional generalizations of the Korteweg-de Vries equation appropriate to the propagation of non-linear ion-acoustic waves are obtained. Soliton solutions are found to exist and they are shown to be stable to two dimensional perturbations.