Abstract:
The nonlinear propagation of small but finite amplitude dust ion-acoustic waves (DIAWs) in an ion-beam driven plasma with Boltzmannian electrons, positive ions and stationary charged dust grains, is studied by using the standard reductive perturbation technique (RPT). It is shown that there exist two critical values $(\gamma_{c1}$ and $\gamma_{c2})$ of ion-beam to ion phase speed ratio $(\gamma)$, beyond which the beam generated solitons are not possible. The effects of the parameters, namely $\gamma$, the ratio of the ion-beam to plasma ion density $(\mu_{i})$, the dust to ion density ratio $(\mu_{d})$ as well as the ion-beam to plasma ion mass ratio $(\mu)$ on both the amplitude and width of the stationary DIAWs are analyzed numerically, and applications of the results to laboratory ion-beam as well as space plasmas (e.g., auroral plasmas) are explained.

Abstract:
We photoionize laser-cooled atoms with a laser beam possessing spatially periodic intensity modulations to create ultracold neutral plasmas with controlled density perturbations. Laser-induced fluorescence imaging reveals that the density perturbations oscillate in space and time, and the dispersion relation of the oscillations matches that of ion acoustic waves, which are long-wavelength, electrostatic, density waves.

Abstract:
The nonlinear theory of two-dimensional ion-acoustic (IA) solitary waves and shocks (SWS) is revisited in a dissipative quantum plasma. The effects of dispersion, caused by the charge separation of electrons and ions and the quantum force associated with the Bohm potential for degenerate electrons, as well as, the dissipation due to the ion kinematic viscosity are considered. Using the reductive perturbation technique, a Kadomtsev-Petviashvili Burgers (KPB)-type equation, which governs the evolution of small-amplitude SWS in quantum plasmas, is derived, and its different solutions are obtained and analyzed. It is shown that the KPB equation can admit either compressive or rarefactive SWS according to when $H\lessgtr2/3$, or the particle number density satisfies $n_0\gtrless 1.3\times10^{31}$ cm$^{-3}$, where $H$ is the ratio of the electron plasmon energy to the Fermi energy densities. Furthermore, the properties of large-amplitude stationary shocks are studied numerically in the case when the wave dispersion due to charge separation is negligible. It is also shown that a transition from monotonic to oscillatory shocks occurs by the effects of the quantum parameter $H$.

Abstract:
We excite ion acoustic waves in ultracold neutral plasmas by imprinting density modulations during plasma creation. Laser-induced fluorescence is used to observe the density and velocity perturbations created by the waves. The effect of expansion of the plasma on the evolution of the wave amplitude is described by treating the wave action as an adiabatic invariant. After accounting for this effect, we determine that the waves are weakly damped, but the damping is significantly faster than expected for Landau damping.

Abstract:
A theory for the ion acoustic wave damping in dense plasmas and warm dense matter, accounting for the Umklapp process, is presented. A higher decay rate compared to the prediction from the Landau damping theory is predicted for high-Z dense plasmas where the electron density ranges from $10^{21}$ to $ 10^{24} \mathrm{cm^{-3}}$ and the electron temperature is moderately higher than the Fermi energy.

Abstract:
The effects of friction on the ion acoustic (IA) wave in fully and partially ionized plasmas are studied. In a quasi-neutral electron-ion plasma the friction between the two species cancels out exactly and the wave propagates without any damping. If the Poisson equation is used instead of the quasi-neutrality, however, the IA wave is damped and the damping is dispersive. In a partially ionized plasma, the collisions with the neutrals modify the IA wave beyond recognition. For a low density of neutrals the mode is damped. Upon increasing the neutral density, the mode becomes first evanescent and then reappears for a still larger number of neutrals. A similar behavior is obtained by varying the mode wave-length. The explanation for this behavior is given. In an inhomogeneous plasma placed in an external magnetic field, and for magnetized electrons and un-magnetized ions, the IA mode propagates in any direction and in this case the collisions make it growing on the account of the energy stored in the density gradient. The growth rate is angle dependent. A comparison with the collision-less kinetic density gradient driven IA instability is also given.

Abstract:
It is generally accepted that the ion acoustic (IA) wave in plasmas containing ions and electrons with the same temperature is of minor importance due to strong damping of the wave by hot resonant ions. In this work it will be shown that the IA wave is susceptible to excitation even in plasmas with hot ions when both an electromagnetic transverse wave and a background density gradient are present in the plasma, and in addition the wave is in fact unstable (i.e., growing) in the case of permeating homogeneous plasmas. The multi-component fluid theory is used to describe the IA wave susceptibility for excitation in inhomogeneous plasmas and its coupling with electromagnetic waves. The growing IA wave in permeating homogeneous plasmas is described by the kinetic theory. In plasmas with density and temperature gradients the IA wave is effectively coupled with the electromagnetic waves. In comparison to ordinary IA wave in homogeneous plasma, the Landau damping of the present wave is much smaller, and to demonstrate this effect a simple but accurate fluid model is presented for the Landau damping. In the case of permeating plasmas, a kinetic mechanism for the current-less IA wave instability is presented, with a very low threshold for excitation as compared with ordinary electron-current-driven kinetic instability. Such growing IA waves can effectively heat plasma in the upper solar atmosphere by a stochastic heating mechanism presented in the work. The results of this work suggest that the IA wave role in the heating of the solar atmosphere (chromosphere and corona) should be reexamined.

Abstract:
An analytical model is presented for the description of nonlinear dust-ion-acoustic waves propagating in an unmagnetized, collisionless, three component plasma composed of electrons, ions and inertial dust grains. The formulation relies on a Lagrangean approach of the plasma fluid model. The modulational stability of the wave amplitude is investigated. Different types of localized envelope electrostatic excitations are shown to exist.

Abstract:
Propagation of arbitrary-amplitude ion-acoustic solitary (IASWs) as well as periodic waves (IAPWs) is investigated in a fully degenerate quantum electron-ion plasma consisting of isothermal- or adiabatic-ion species. It is shown that the system dimensionality and degrees of freedom play critical roles in matching criteria for propagation of such waves. Furthermore, it is revealed that for the case of adiabatic-ion unlike isothermal one, in some cases, there exists an upper fractional ion-temperature limit for the existence of IAPWs. It is also shown that, the variations of wave-amplitude with respect to the change in fractional ion-temperature is quite different for the cases of isothermal and adiabatic-ion plasmas.

Abstract:
A simulation study is performed to investigate the dynamics of coupled Langmuir waves (LWs) and ion-acoustic waves (IAWs) in an unmagnetized plasma. The effects of dispersion due to charge separation and the density nonlinearity associated with the IAWs, are considered to modify the properties of Langmuir solitons, as well as to model the dynamics of relatively large amplitude wave envelopes. It is found that the Langmuir wave electric field, indeed, increases by the effect of ion-wave nonlinearity (IWN). Use of a low-dimensional model, based on three Fourier modes shows that a transition to temporal chaos is possible, when the length scale of the linearly excited modes is larger than that of the most unstable ones. The chaotic behaviors of the unstable modes are identified by the analysis of Lyapunov exponent spectra. The space-time evolution of the coupled LWs and IAWs shows that the IWN can cause the excitation of many unstable harmonic modes, and can lead to strong IAW emission. This occurs when the initial wave field is relatively large or the length scale of IAWs is larger than the soliton characteristic size. Numerical simulation also reveals that many solitary patterns can be excited and generated through the modulational instability (MI) of unstable harmonic modes. As time goes on, these solitons are seen to appear in the spatially partial coherence (SPC) state due to the free ion-acoustic radiation as well as in the state of spatiotemporal chaos (STC) due to collision and fusion in the stochastic motion. The latter results the redistribution of initial wave energy into a few modes with small length scales, which may lead to the onset of Langmuir turbulence in laboratory as well as space plasmas.