Search

Particle collisions can have significant effects on plasma instabilities, especially in dense and/or low temperature plasmas. To understand the influence of collisional effects on the plasma waves, the Vlasov–Poisson system with Krook collisions is applied to study the long-term evolution of the two-stream (TS) and bump-on-tail (BOT) instabilities. The system is solved numerically with the fourth-order Runge–Kutta scheme and the Thomas algorithm. It is found that collisions can enhance the wave damping and mitigate the energy of the characteristic slow evolving nonlinear Landau damping oscillations associated with the wave-trapped electrons, especially if the collision rate ν is higher than 0.01 ω p , where ωp is the plasma frequency of the background plasma. Collisions can also decrease the growth rate and saturation level of the TS and BOT unstable waves and tend to shrink the phase space vortex and narrow the phase-mixed region of the trapped electrons. However, our simulations show that collisions cannot readily prevent the nonlinear Landau damping oscillations. In fact, only with ν > 0.001 ω p for the TS instability and ν > 0.01 ω p for the BOT instability, as well as evolution times greater than several hundred ω p − 1 , the vortex structure of the wave-trapped electrons can be undetectable. The corresponding growth rates also drop dramatically, and the maximum wave energy can be one or two orders lower than that of the collisionless limits. [ABSTRACT FROM AUTHOR]

The evolution of a small spatially periodic perturbation in the electron velocity distribution function in collisionless plasma is reconsidered by numerically solving the Vlasov and Poisson equations. The short as well as long time behaviors of the excited oscillations and damping/ modulation are followed. In the small but finite-amplitude excited plasma wave, resonant electrons become trapped in the wave potential wells and their motion affects the low-velocity electrons participating in the plasma oscillations, leading to modulation of the latter at an effective trapping frequency. It is found that the phase space of the resonant and low-velocity electrons becomes chaotic, but then self-organization takes place but remains fine-scale chaotic. It is also found that as long as particles are trapped, there is only modulation and no monotonic damping of the excited plasma wave. The modulation period/amplitude increases/decreases as the magnitude of the initial disturbance is reduced. For the initial and boundary conditions used here, linear Landau damping corresponds to the asymptotic limit of the modulation period becoming infinite, or no trapping of the resonant electrons. [ABSTRACT FROM AUTHOR]

Temporal plasma wave echoes are investigated by solving the Vlasov-Poisson system numerically in detail. The time of appearance and the structure of the echoes, including that of the higher harmonics and the dependence on the time between the excitations, are found to agree well with that from theory and/or experiments. Although Landau damping strongly depends on the small number of in-phase (with the excited plasma waves) electrons, the latter do not noticeably affect echo formation even after they become trapped in the small but finite wave field. As expected, when one or both of the excitations become too strong, the number of trapped particles can become so large that the plasma echo ceases to exist. [ABSTRACT FROM AUTHOR]

Fully nonlinear quasistationary wake plasma waves excited by and comoving with a charged pulses are investigated. The characteristics of the excited plasma wave depend on a (nonlinear) resonance between the wave and the pulse. With two comoving driver pulses, localized wake structures without the long wakes can be produced. [ABSTRACT FROM AUTHOR]

Electrostatic plasma waves in an adiabatic electron-positron plasma are investigated nonperturbatively. It is shown that quasistationary large-amplitude waves with smooth as well as highly peaked profiles can appear. In the peaked waves, the electron and positron peaks may be separated by large distances, but no completely isolated soliton-like structures were found. [ABSTRACT FROM AUTHOR]

The reshaping of intense laser pulse by vacuum capillary is studied by particle-in-cell simulation. It is shown that as an intense laser pulse propagates from free space into a capillary, its profile is reshaped due to laser-plasma interaction near the entrance of capillary. As a result, the free-space mode is self-consistently converted into a capillary mode. Only the relatively low-intensity periphery of the reshaped pulse interacts with the capillary-wall plasma, so that the high-intensity center of the pulse can propagate in the narrow vacuum channel over a distance much larger than the Rayleigh length. The mechanism is then applied to reshape a radially imperfect laser pulse having two wings around the center spot. Most of the output light energy is concentrated in the center spot, and the wings are almost completely removed. That is, the quality of the laser pulse can be greatly improved by a capillary. [ABSTRACT FROM AUTHOR]

Generation of high-energy proton bunch in the interaction of a high-power laser pulse with a complex target consisting of a front horizontal slice adjoining a conventional heavy ion and proton double-layer slab is investigated using two-dimensional particle-in-cell simulation. The laser pulse propagates along both sides of the slice. A large number of hot electrons are generated and accelerated by the surface ponderomotive force, and transported through the double layer, forming a backside sheath field which is considerably stronger and more localized than that produced by the electrons from a simple double layer. As a result, the protons in the proton layer can be accelerated to energies more than three times, and the energy spread halved, that from the simple double layer. [ABSTRACT FROM AUTHOR]

Formation of dusty plasmas in the Earth’s ionosphere at 80–120 km altitudes during high-speed meteor showers and its detectable manifestations are discussed. Emphasis is given to ground-based observations such as detection of low-frequency (<50 Hz) ionospheric radio noise, ground-based observations of infrasonic waves, and amplification of the intensity of green radiation at 557.7 nm from a layer at the 110–120 km altitude in the lower ionosphere. The physical processes responsible for these manifestations are considered. [ABSTRACT FROM AUTHOR]

A fluid theory of void formation in dusty plasmas taking into account ionization is proposed. It is shown that if the ionization rate is larger than a threshold, an initial steady-state dust-density distribution can evolve into a stable distribution containing a void. As the ionization rate is further increased, the time required for void formation decreases. The void size first increases, but then decreases. However, for still larger ionization rates, the dusty region of the plasma becomes ringlike, including the convection term in dust momentum equation. The results are in agreement with existing experiments and theories. [ABSTRACT FROM AUTHOR]

Nonlinear coupling between the radial, axial, and azimuthal flows in a cold rotating plasma is considered nonperturbatively by first constructing a basis solution for a rotating flow. Simple but exact solutions that describe an expanding plasma with oscillatory flow fields are then obtained. These solutions show that the energy in the radial and axial flow components can be transferred to the azimuthal component but not the vice versa. Nonlinear electron velocity oscillations in the absence of electron density oscillations at the same frequency are shown to exist. [ABSTRACT FROM AUTHOR]

The existence of a two-parameter set of dressed Langmuir solitons is shown numerically, resolving a discrepancy among earlier investigations. [ABSTRACT FROM AUTHOR]

Discusses evolution equations governing large amplitude waves in cold plasma columns bounded by deformable dielectrics. Possible existence of exact solutions for finite amplitude electron plasma waves in low-temperature plasmas cylindrically bounded by rigid containers; Chaotic behavior exhibited by several solutions.

The relation between several magnetic waves and instabilities is clarified. These modes involve only electron dynamics. It is shown that in the parameter regime of interest there are no propagating unstable waves driven by the first order baroclinic effect. [ABSTRACT FROM AUTHOR]

An exact solution is obtained for large amplitude volume and surface waves driven by an external electric field oscillating at double the surface-wave frequency in a cold cylindrical plasma bounded by a rigid dielectric. [ABSTRACT FROM AUTHOR]

A generalized theory of dust-acoustic waves in strongly coupled dusty plasmas containing variable-charge dusts or impurities is given. Relaxation processes associated with the strong coupling, as well as dust-charge variation, are taken into account. It is shown that the dispersion and damping properties of the waves are strongly affected by dust-dust correlation, dust charging and viscoelastic relaxations, and dust-neutral collisions. Multiple transitions between positive to negative dispersions are also found and discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The propagation of dust acoustic surface waves on a thin dusty plasma slab is investigated. The dispersion relation for the waves is found to differ significantly from that for infinite plasmas. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]