The propagation of surface waves on a semi-bounded quantum plasma is investigated taking into account the collisional effects. The quantum hydrodynamic model includes Bohm's quantum force, Fermi-Dirac statistical, and collisional corrections are used to derive the dispersion relation of these waves. It is shown that the collisions play a significant role on the decay of surface wave amplitude. Furthermore, the surface waves can be unstable in the presence of collisional effects. It is also indicated that the growth rate of the surface wave instability increases with the increase of collisional and quantum effects, especially in the high wavenumber region. V C 2012 American Institute of Physics. [http://dx.

The evolution of filamentation instability in a weakly ionized current-carrying plasma with nonextensive distribution was studied in the diffusion frequency region, taking into account the effects of electron-neutral collisions. Using the kinetic theory, Lorentz transformation formulas, and Bhatnagar-Gross-Krook collision model, the generalized dielectric permittivity functions of this plasma system were achieved. By obtaining the dispersion relation of low-frequency waves, the possibility of filamentation instability and its growth rate were investigated. It was shown that collisions can increase the maximum growth rate of instability. The analysis of temporal evolution of filamentation instability revealed that the growth rate of instability increased by increasing the q-parameter and electron drift velocity. Finally, the results of Maxwellian and q-nonextensive velocity distributions were compared and discussed.

The nonlinear coupling between circularly polarized electromagnetic (CPEM) waves and acoustic-like waves in a magnetoactive electron-positron-ion (e-p-i) plasma is studied, taking into account the relativistic motion of electrons and positrons. The possibility of modulational instability and its growth rate as well as the envelope soliton formation and its characteristics in such plasmas are investigated. It is found that the growth rate of modulation instability increases in the case that ωc/ω<1 (ωc and ω are the electron gyrofrequency and the CPEM wave frequency, respectively) and decreases in the case that ωc/ω>1. It is also shown that in a magnetoactive e-p-i plasma, the width of bright soliton increases/decreases in case of (ωc/ω)<1/(ωc/ω)>1 by increasing the magnetic field strength.

The low-frequency instabilities in the interaction between an ion beam and a magnetoactive plasma are investigated taking into account the effects of the dissipation and thermal motion of the charged particles. Furthermore, the effects of magnetic field strength, ion beam velocity, and propagation angle on the resonance frequency and the growth rate of the instabilities are studied. It is shown that, according to the strength of the magnetic field and the ion beam velocity, the increase of the thermal velocity of the charged particles can increase or decrease the resonance frequency in the ion acoustic frequency range.Index Terms-Ion-beam-plasma interaction, low-frequency instabilities, magnetoactive plasma.

The modulational instability of right-hand circularly polarized electromagnetic electron cyclotron (CPEM-EC) wave in a magnetized quantum plasma is studied taking into account the collisional effects. Employing quantum hydrodynamic and nonlinear Schrödinger equations, the dispersion relation of modulated CPEM-EC wave in a collisional plasma has been derived. It is found that this wave is unstable in such a plasma system and the growth rate of the associated instability depends on various parameters such as electron Fermi temperature, plasma number density, collision frequency, and modulation wavenumber. It is shown that while the increase of collision frequency leads to increase of the growth rate of instability, especially at large wavenumber limit, the increase of plasma number density results in more stable modulated CPEM-EC wave. It is also found that in contrast to collisionless plasma in which modulational instability is restricted to small wavenumbers, in collisional plasma, the interval of instability occurrence can be extended to a large domain.