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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]

Precision spectroscopy of molecular hydrogen can be used to test the quantum electrodynamics theory and determine the proton-to-electron mass ratio in a four-body system. Cavity-enhanced double-resonance spectroscopy is proposed to determine highly-excited rotation-vibration energies of HD with high precision. As a demonstration, the V-type comb-locked cavity-assisted double resonance (COCA-DR) spectroscopy of HD is measured by pumping the P(1) (2-0) line and probing the R(1) line in the same overtone band. The sum value of the two transition frequencies is determined to be 426 889 423 917 (26) kHz, representing a new test of theoretical calculations. [ABSTRACT FROM AUTHOR]

The acceleration of protons in dense plastic foils irradiated by ultrahigh intensity laser pulses is simulated using a two-dimensional hybrid particle-in-cell scheme. For the chosen parameters of the overdense foils of densities ρ=0.2, 1, and 3 g/cm3 and of an ultrahigh intensity (2×1020 W/cm2) laser pulse, our simulations illustrate that a high-density target is favorable to high collimation of the target-normal-sheath acceleration protons but less energy for a short acceleration time (<100 fs). In particular, the difference of strong local heating of the carbon ion for different plasma densities is clearly observed at both the front and rear surfaces of thin solid targets, suggesting that the effect of the density and composition of the targets are also important for correctly simulating energetic ion generation in ultraintense laser-solid interactions. [ABSTRACT FROM AUTHOR]

Generation of a thin plasma jet with embedded gigagauss axial magnetic fields from the frontal impact of a short linearly polarized laser pulse on an overdense microtube target is considered. It is a new scheme of axial magnetic field generation without initial laser angular momentum. Three-dimensional particle-in-cell simulations show that the space-charge field of the laser expelled tube-front electrons will pull out carbon ions to form at the tube entrance a long-living low-density plasma bunch with gigagauss magnetic fields. The front center of the plasma bunch then stretches forward to form a thin gigagauss-magnetized plasma jet, which survives for sub-picosecond after the core of the laser has passed through the tube. [ABSTRACT FROM AUTHOR]

Background: Because of the close relationship between seed coat color and forage seed quality, it is of great significance to reveal the effect of seed coat color on seed germination and seedling growth under drought stress. Methods: We explore the effect of different seed coat colors (yellow, dark brown) on the seed germination and seedling growth of alfalfa under simulated drought stress (polyethylene glycol (PEG-6000) with eight osmotic potentials: 0 MPa, -0.1 MPa, -0.2 MPa, -0.3 MPa, -0.4 MPa, -0.6 MPa, -0.8 MPa, -1.0 MPa). Result: Under control conditions, the germination rate and germination energy of yellow seeds (91.6% and 91.2%, respectively) were higher than dark brown seeds (46.2% and 42.0%). The maximum seed germination rate and germination energy were observed in the -0.1MPa treatment for both yellow and dark brown seeds and were higher than control by 1.53% and 0.66% (yellow) and 9.96%, 14.76% (dark brown), respectively. The root length and seedling growth of two kinds of seeds were significantly inhibited when drought intensity increased. In summary, the germination and seedling growth traits of yellow seeds were much better than dark brown ones. Agronomically, selecting seed with high proportions of yellow coat color is more beneficial for seed storage and establishment of new alfalfa grasslands. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the effect of charged particulates or dust particles on surface wave produced microwave discharges. Formulation; Calculation of frequencies of standing electromagnetic eigenmodes of a large-area of flat plasmas; Discussion.

A normalized weighting function model for the average period of particles trapped in the potential wells of waves undergoing nonlinear Landau damping is considered. The model preserves the conservation properties of the trapped particles and relates them to the evolution of the wave envelope. It is valid when there are more shallowly trapped particles than deeply trapped particles, such as in long-time nonlinear Landau damping, as well as stabilities due to trapped particles at long times. The model is also useful for estimating the validity of the often invoked assumption that most trapped particles in nonlinear waves are deeply trapped. [ABSTRACT FROM AUTHOR]

Intense attosecond light sources are required for investigating ultrafast electron dynamics, such as that in molecules and atoms, etc. However, so far the achievable photon energy remains at the keV level, thereby limiting their range of applications. For instance, probing intranuclear dynamics requires photon energies in the gamma-ray regime. We propose here a scheme for generating intense attosecond gamma-ray pulses by irradiating a thin solid-density foil with intense vortex laser. In the interaction, the laser driven-foil electrons are differentially accelerated within a quarter-wave field and become highly bunched. Three-dimensional particle-in-cell simulations show that they can efficiently (with ∼ 30 % energy conversion efficiency) radiate ultrashort ( ∼ 400 as), high-flux ( > 10 10 photons per pulse), and ultrabrilliant (up to 1027 photons s−1 mm−2 mrad−2 per 0.1% BW at 1 MeV photon energy) gamma rays. With an x-ray driving laser, the scheme can even produce isolated bright sub-attosecond gamma-ray pulses that are useful for time-resolved nuclear spectroscopy and many other areas. [ABSTRACT FROM AUTHOR]

Expansion of the ion and electron fronts of a cold non-neutral plasma slab with a quasi-neutral core bounded by layers containing only ions is investigated analytically and exact solutions are obtained. It is found that on average, the plasma expansion time scales linearly with the initial inverse ion plasma frequency as well as the degree of charge imbalance, and no expansion occurs if the cold plasma slab is stationary and overall neutral. However, in both cases, there can exist prominent oscillations on the electron front. [ABSTRACT FROM AUTHOR]

Excitation of streamers by modulationally unstable small-scale drift-Alfven wave (SSDAW) is investigated. It is found that the excitation depends strongly on the propagation direction of the SSDAW, and the ion and electron diamagnetic drift waves are both unstable due to the generation of streamers. It is also shown that zonal flows can be effectively excited by the SSDAW with the propagation direction different from that for streamer excitation. [ABSTRACT FROM AUTHOR]

Turbulence governed by a generalized nonlinear Schrödinger equation (GNSE) including viscous heating and nonlinear damping is numerically investigated. It is found that a large localized pulse can suffer modulational instability and then collapse into the shortest-wavelength modes, as for the classical nonlinear Schrödinger equation. However, the total energy of the nonconservative GNSE can also become constant during the collapse via local balance of energy gain and loss in the phase space. After the collapse, instead of inverse cascading into a state of strong turbulence with broad spectrum, a single-step cascade, or condensation, into modes of one predominant wavelength can occur. In fact, after attaining total energy balance the turbulent system as a whole evolves like a closed adiabatic system. [ABSTRACT FROM AUTHOR]

Radial expansion of an ionizing gas or plasma cylinder into vacuum is investigated. An exact model for the evolution of the density and velocity fields of the electrons, ions, and neutrals, including the effect of photo and electron-impact ionization on the flow characteristics is developed and solutions obtained. A quasineutral nonlinear electrostatic mode involving rapid oscillations in the electron velocity but not in the density can occur in the expanding plasma. The mode turns out to be almost unaffected by weak ionization. [ABSTRACT FROM AUTHOR]

A two-dimensional generalized cubic nonlinear Schrödinger equation with complex coefficients for the group dispersion and nonlinear terms is used to investigate the evolution of a finite-amplitude localized initial perturbation. It is found that modulation of the latter can lead to sideband formation, wave condensation, collapse, turbulence, and inverse energy cascade, although not all together and not in that order. [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]

Nonlinear coupling of the motion in the three spatial degrees of freedom of a cold fluid electron-positron plasma is investigated. Exact solutions describing expanding flows with oscillations are obtained. It is found that the energy in the irrotational flow component is in general transferred to the rotational components, but not in the reversed direction. Furthermore, since the density evolution need not be related to all the three flow components, oscillations in one or two of the flow fields can be purely electromagnetic and are not accompanied by density oscillations. [ABSTRACT FROM AUTHOR]

The electric potential and the electron- and ion-density profiles near a spherical probe in electronegative plasmas containing negative as well as positive ions are studied. It is shown that for relatively large probe radius and neutral-gas pressure, and/or small electron-to-ion temperature ratio, the density profile of the negative ions can differ from that of Boltzmann if their flux near the probe is outwards. The existence of stationary states is considered and the corresponding maximum negative-ion flux is obtained. [ABSTRACT FROM AUTHOR]

The electric and the positive- and negative-ion drag forces on a dust grain in an electronegative complex plasma are investigated. It is shown that the number of locations where the drag forces balance the electric force is considerably larger than that in an electropositive plasma. The balance occurs in the so-called oscillation regime where the electric field oscillates in space. The effect of the negative-ion drag force on the dust grain can be substantial in a certain parameter range. [ABSTRACT FROM AUTHOR]

A complex low-pressure argon discharge plasma containing dust grains is studied using a Boltzmann equation for the electrons and fluid equations for the ions. Local effects, such as the spatial distribution of the dust density and external electric field, are included, and their effect on the electron energy distribution, the electron and ion number densities, the electron temperature, and the dust charge are investigated. It is found that dust particles can strongly affect the plasma parameters by modifying the electron energy distribution, the electron temperature, the creation and loss of plasma particles, as well as the spatial distributions of the electrons and ions. In particular, for sufficiently high grain density and/or size, in a low-pressure argon glow discharge, the Druyvesteyn-like electron distribution in pristine plasmas can become nearly Maxwellian. Electron collection by the dust grains is the main cause for the change in the electron distribution function. [ABSTRACT FROM AUTHOR]

Electron acceleration from the interaction of an intense short-pulse laser with low density plasma is considered. The relation between direct electron acceleration within the laser pulse and that in the wake is investigated analytically. The magnitude and location of the ponderomotive-force-caused charge separation field with respect to that of the pulse determine the relative effectiveness of the two acceleration mechanisms. It is shown that there is an optimum condition for acceleration in the wake. Electron acceleration within the pulse dominates as the pulse becomes sufficiently short, and the latter directly drives and even traps the electrons. The latter can reach ultrahigh energies and can be extracted by impinging the pulse on a solid target. [ABSTRACT FROM AUTHOR]

Lagrangian variables are used to describe linear and nonlinear oscillations of a magnetized non-neutral plasma slab in a harmonic trap, for slab width larger or comparable to the Debye length. The plasma particles move along the magnetic field lines, so that the oscillations are one-dimensional. The oscillation spectrum is found analytically, and the thermal corrections to the frequencies are calculated in a nonperturbative manner. Simple exact nonlinear solutions for the low-order modes are also obtained. [ABSTRACT FROM AUTHOR]

Ambipolar diffusion of electrons and ions in a plasma containing charged dust grains is investigated. As the diffusion is on the ion time scale, the dust distribution remains stationary but the dust charge can vary. An analytical solution showing that the presence of dusts can significantly increase the diffusion length is given. Other solutions of practical interest are obtained numerically. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ambipolar diffusion of plasma particles in a column of inhomogeneous plasma containing dust grains is investigated analytically as well as numerically. The grains act as charge sinks and behave like an immobile but charge-varying negative background. They can lead to significant depletion of the electron density and decrease the diffusion scale length. The theoretically obtained election density distribution agrees well with that from experiment. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A class of exact one-dimensional oscillating solutions of the Vlasov–Poisson system describing a one-component plasma in a parabolic electrostatic potential well is considered. Through a separation of variables procedure, a system of ordinary differential equations describing the moments of the velocity distribution function is obtained. The moment equations can be decoupled at any order from the higher ones without approximations. Oscillating-pattern solutions for the resulting finite and exact systems are found. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies current-driven dust ion-acoustic instability in a collisional dusty plasma. Effects of dust-charge variation, electron and ion capture; Dissipative mechanisms leading to the changes of the particles momenta.

A traditional cold-plasma boundary model is revised to allow for proper description of nonlinear effects in surface wave propagation. It is shown that induced nonlinear surface currents can exist at the boundary. As an example, the third-order ponderomotive phenomena are considered, and the effect of the boundary condition on these nonlinear interactions is examined. [ABSTRACT FROM AUTHOR]

The self-similar expansion of two species of dust particles in an equilibrium plasma is investigated by means of fluid as well as Vlasov theories. It is found that under certain conditions the density of the dust with the smaller charge-to-mass ratio can vanish at a finite value of the self-similar variable, while the density of the remaining dust species attains a plateau. The kinetic theory predicts a secondary decay in which the latter density eventually also vanishes. [ABSTRACT FROM AUTHOR]

The effect of dust particles or impurity ions on plasma-wall interaction is investigated using simple fluid models, it is shown that the behavior of the electrostatic potential as well as the particle densities can be considerably different from that of a two-component plasma. [ABSTRACT FROM AUTHOR]

The one-dimensional quasineutral self-similar expansion of a dusty plasma is investigated using kinetic theory. The light electrons and ions are assumed to be in local thermodynamic equilibria and the heavy multiply charged dust particles collisionless. It is found that, within a few τ’s, where τ is the self-similar variable, the velocity distribution of the dust particles becomes highly asymmetrical and narrow, and the dust density vanishes. [ABSTRACT FROM AUTHOR]

Particle-in-cell simulation and analytical modeling demonstrate that the reflection of a single-cycle light pulse from a thin target can produce an ultrashort ultraintense electromagnetic field. [ABSTRACT FROM AUTHOR]

It is pointed out that the multispecies model for identical particles is in general not suitable for considering quasistationary nonlinear plasma structures. For phenomena on long time scales, the a priori partitioning of electrons into hot and cold species is often unrealistic unless the latter are actually separated in the phase space by external or self-consistent fields. [ABSTRACT FROM AUTHOR]

The growth of single-walled carbon nanotubes (SWCNTs) in plasma-enhanced chemical vapor deposition (PECVD) is studied using a surface diffusion model. It is shown that at low substrate temperatures (<=1000 K), the atomic hydrogen and ion fluxes from the plasma can strongly affect nanotube growth. The ion-induced hydrocarbon dissociation can be the main process that supplies carbon atoms for SWCNT growth and is responsible for the frequently reported higher (compared to thermal chemical vapor deposition) nanotube growth rates in plasma-based processes. On the other hand, excessive deposition of plasma ions and atomic hydrogen can reduce the diffusion length of the carbon-bearing species and their residence time on the nanotube lateral surfaces. This reduction can adversely affect the nanotube growth rates. The results here are in good agreement with the available experimental data and can be used for optimizing SWCNT growth in PECVD. [ABSTRACT FROM AUTHOR]

Oscillations of charged dust grains in the sheath region of a radio-frequency plasma containing negative ions are studied using a one-dimensional model for collisional sheaths. The forces on a dust grain in the sheath region are first analyzed and the force-balance conditions found. Oscillations of the levitated dusts are then investigated. Linear lattice waves, including one-dimensional longitudinal and two-dimensional hexagonal transverse lattice waves, as well as the effects of the negative ions and external magnetic field on the waves, are discussed. [ABSTRACT FROM AUTHOR]

Investigates the operation and mode jumps in low-frequency radio-frequency inductively coupled plasmas. Excitation of the electrostatic and electromagnetic discharge modes by a flat inductive coil; Examination of the power transfer efficiency and mode transition behavior; Increase of the discharge efficiency after the transition to the H discharge regime.

Shock structures in plasmas containing variable-charge macro particles are shown to exist because of an effective dissipation associated with charging of the latter. © 1996 American Institute of Physics. [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]

It is shown that a high power laser can parametrically generate magnetic electron drift motion in a high density, nonuniform collisional plasma. The nonlinear dispersion relation as well as the growth rates of the decay and modulational instabilities are obtained. Possible application of these results in laser-plasma interaction is discussed. [ABSTRACT FROM AUTHOR]

The general set of low-frequency nonlinear fluid equations describing microturbulence in an inhomogeneous warm plasma with a strong magnetic field is shown to possess two-dimensional solitary vortex solutions. [ABSTRACT FROM AUTHOR]

Techniques of plasma surface wave theory are introduced to obtain new results for magnetic electron waves at the interface of two plasma regions with distinct properties. The procedure generalizes and simplifies problems involving sharp density jumps often encountered in laser– or beam–plasma interaction. As an example, a new magnetic instability is discussed. [ABSTRACT FROM AUTHOR]

Localized double vortices associated with the flute modes are shown to exist. Special emphasis is given to the effect of the convective variation of the fluid magnetic moment. It is shown that the latter effect considerably modifies the existence regions of the vortices. [ABSTRACT FROM AUTHOR]

The solitary vortex solution is shown to exist for the set of nonlinear equations describing lowfrequency fluid motion in a magnetized plasma. [ABSTRACT FROM AUTHOR]

An all-optical method for generating ultra-intense high-order-mode light pulse is investigated with three-dimensional particle-in-cell simulation. We find that the conversion from a short intense circularly polarized incident Gaussian laser pulse into a transverse magnetic (TM) mode occurs as it propagates into a micro plasma waveguide. The strength of the longitudinal electric field of the excited TM modes can be almost two orders of magnitude higher than that of the original laser. The simulation results show that, for the lower-order modes, the trapped electrons lead to their revolving transverse structures. A linear plasma waveguide model is presented to predict the mode pattern and intensity of the longitudinal electric fields, which are in excellent agreement with those in the simulations. Relativistic-intense high-order-mode light can be useful for many applications, including accelerating charged particles to high energies. [ABSTRACT FROM AUTHOR]

The acceleration of protons from the interaction of two intersecting laser pulses in a double-layer target, consisting of a carbon slab with a thin hydrogen layer behind it, is investigated. It is found that a bunch of well-collimated, up to 270 MeV, quasi-monoenergetic protons can be generated. The affected target electrons are heated and accelerated forward by the laser pulses so that the target gradually becomes transparent as the lasers bore into it. Eventually, the thin target becomes fully transparent. The converging laser pulses can then pass through it and the hot backside electron cloud, together with the electrons trapped in them. As a result, behind the target, an inhomogeneous sheath electric field is formed, which not only accelerates the protons but also merges them into a quasi-monoenergetic bunch with low divergence. The energy and spatial spread of the bunch, as well as the peak energy, can be controlled by manipulating the locations of the two lasers. [ABSTRACT FROM AUTHOR]

Long distance propagation of an energetic laser pulse with intensity slightly below that for multi-photon ionization in air is considered analytically, by noting that in the process, it is mainly the peak region of the pulse that interacts with the air molecules. Similar to that of much shorter femtosecond laser pulses of similar intensity, the affected air becomes slightly ionized and self-consistently forms a co-propagating thin and low-density plasma filament along the axis. It is found that a hundred-Joule-level laser pulse with a relatively large spot radius and pulse duration can propagate (also in the form of a self-consistent filament) tens of kilometers through the atmosphere. Such laser propagation properties should have applications in many areas. [ABSTRACT FROM AUTHOR]

Smooth as well as cusped oscillating periodic structures on plasma-vacuum interface are shown to exist. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The theory for nonlinear electrostatic surface waves on a cold semi-infinite plasma is generalized to include an external driving force. An oscillon solution is found. [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]

Ion acceleration from the interaction of two intersecting intense laser pulses with an overdense plasma is investigated using a three-dimensional particle-in-cell simulation. It is found that, comparing with the single-pulse case, the charge of the resulting energetic ion bunch can be increased by more than an order of magnitude without much loss of quality. Dependence of the ion charge on the interaction parameters, including separation distance and incidence angles of the lasers, is considered. It is shown that the charge of the accelerated ion bunch can be optimized by controlling the degree of laser overlapping. The improved performance can be attributed to the enhanced laser intensity as well as stochastic heating of the accelerated electrons. Since at present the intensity of readily available lasers is limited, the two pulse scheme should be useful for realizing higher laser intensity in order to achieve higher-energy target normal sheath acceleration ions. [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]

Discusses the applicability of the dust charging model used by Sharma and Sugawa in an article published in the 1998 issue of 'Physics of Plasma.' Instability of dust ion cyclotron waves due to Cherenkov-type interaction with an ion beam in a plasma containing variable-charge dusts; Need for a more accurate account of the external magnetic field in the model.