B. Buti

Ion acoustic solitary waves in a two-electron-temperature plasma

Due to the presence of a relatively cold electron component in a plasma, the ion acoustic solitary wave of a given width has a larger amplitude. When the temperature difference between the two electron components is sufficiently large, the strength of dispersion is reduced to an extent that a solitary solution is no longer possible.

Exact electron-acoustic solitary waves

Nonlinear propagation of an electron-acoustic wave in a magnetoplasma is considered. Accounting for the exact electron and ion nonlinearities, we show that the equations governing the dynamics of these waves can be written in terms of the energy integral of a classical particle. A careful analysis of the potential reveals the existence of exact planar solitary waves. Application of our investigation to space plasmas is pointed out.

Hamiltonian systems with indefinite kinetic energy

Some interesting features of a class of two-dimensional Hamiltonians with indefinite kinetic energy are considered. It is shown that such Hamiltonians cannot be reduced, in general, to an equivalent dynamical Hamiltonian with positive definite kinetic energy quadratic in velocities. Complex nonlinear evolution equations like the K-dV, the MK-dV and the sine-Gordon equations possess such Hamiltonians. The case of complex K-dV equation has been considered in detail to demonstrate the generic features. The two-dimensional real systems obtained by analytic continuation to complex plane of one-dimensional dynamical systems are also discussed. The evolution equations for nonlinear, amplitude-modulated Langmuir waves as well as circularly polarized electromagnetic waves in plasmas, are considered as illustrative examples.

Langmuir solitons in a two-temperature plasma

The existence of finite-amplitude Langnwir solitary waves in a two-electron-temperature plastia is investigated. A now type of soliton, in which the density depression and the electric field amplitude scale in the same manner, and which travels at the effective sound speed, has been found.

Effect of hot ions on ion acoustic solitons and holes

Abstract In a two-electron-component plasma, we have investigated the effect of hot ions by retaining the full nonlinearities. Even an extremely small ion temperature can drastically reduce the maximum amplitude for solitons as well as holes.

Exact nonlinear alfvén waves

Abstract Exact localized nonlinear Alfven waves are investigated by retaining the complete ion nonlinearity and the finite-β effects. Solitary waves with a density hump and a density dip are found to exist.

Electron-acoustic and ion-ion hybrid resonance-drift instability in inhomogeneous multi-ion-species magnetoplasmas

Electron-acoustic (EA) and ion-ion-hybrid resonance (IIHR) waves, in a multi-ion-species magnetoplasma with density gradients perpendicular to the magnetic field and the direction of wave propagation are found to be drift unstable provided the inhomogeneities exceed a certain threshold. The possibility of mode conversion between the EA and the IIHR waves is examined.

Modulational Instability of Ion-Acoustic Waves in Collisional Plasmas

Nonlinear ion-acoustic waves, which in the absence of collisions are moderately stable in the long wave length limit, become modulationally unstable due to presence of collisions. These waves are unstable in the wave number range kmin < k < kmax.

Modulational instability of ion-acoustic-waves in two electron temperature plasmas

The envelope properties of ion-acoustic waves in a two-electron-temperature plasma are studied. The nonlinear Schrödinger equation describing the envelope of these waves is obtained from the plasma fluid equations by employing the Krylov-Bogoliubov-Mitropolsky perturbation method. It is shown that the ion-acoustic waves can be modulationally unstable or stable depending on the ratios of the densities and the temperatures of the hot and the cold electron components. Even a small fraction of the cold electron component can drastically affect the stability of the system.

Return current instability and its effects on beam-plasma system

The return current induced in a plasma by a relativisitc electron beam generates a new electron-ion two-stream instability (return current instability). Although the effect of these currents on the beam-plasma e-e instability is negligible, there exists a range of wave numbers which is unstable only to return current (RC) instability and not to e-e instability. The electromagnetic waves propagating along the direction of the external magnetic field, in which the plasma is immersed, are stabilized by these currents but the e.m. waves with frequencies,ω2≪Ωe2≪ωpe2 (Ωe andωpe being cyclotron and plasma frequency for the electrons of the plasma respectively) propagating transverse to the magnetic field get destabilized. Heuristic estimates of plasma heating, due to RC instability and due to decay of ion-acoustic turbulence generated by the return current, are made. The fastest time scale on which the return current delivers energy to the plasma due to the scattering of ion-sound waves by the electrons can be ∼ωpi−1 (ωpi being the plasma frequency for the ions).