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A simple model including the effects of initial velocity, air drag, gravity, and electrostatics on the dynamics of airborne droplets emitted from humans is presented. It is found that relatively large droplets can also travel far if their charge and/or the atmospheric electric field is sufficiently large.

We propose to use intense optical vortex to control laser-based ion acceleration for obtaining high-quality ion beams. An acceleration field favorable for generating well-collimated energetic proton beams results from the interaction of a tailored vortex laser pulse with thin solid-density foil in a blowout regime. Three-dimensional particle-in-cell simulations show that the foil protons can be efficiently accelerated to the GeV level in the form of a beam with small radius (μm), narrow divergence (π mm mrad). The proton beam is of high energy density (>1018 J m−3) and high brightness (>1022 A m−2 rad−2), exceeding that of the Gaussian laser case by four orders of magnitude, and the energy conversion efficiency is about 12 times that under the same laser intensity. The scheme can also be used to accelerate heavier, such as carbon, ions. The resulting ion beams should be useful as compact neutron source, for creation of warm dense matters, as well as ion-beam direct and indirect drive inertial confinement fusion, ultrafast diagnostics of the implosion dynamics in the latter, etc.

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.

Transport of moderate relativistic micro electron beam in overdense plasma is investigated using numerical simulation and analytical modeling. It is found that if the product of the initial beam current density jb and radius R0 is above a lower limit, which scales like , where ne is the plasma density, the beam will periodically self pinch and relax as it propagates. Otherwise the beam diverges. But if is too large, the pinching behavior becomes quite different. Such micro-beam transport behavior can be attributed to the nonlinear dynamics of the beam electrons in overdense plasma.

Time evolution of ionospheric D-region plasmas including the perturbations of electrons and charged aerosol particles is investigated under the conditions of polar mesosphere summer echoes (PMSE). It is shown that the time scale of decay of the electron density is in the order of an hour under typical PMSE conditions, in the majority of cases, the electron density is anticor-related to the ion density, except that the radius of aerosol particles is greater than 50 nm. Also, the evolutions under varied parameters, such as the amplitude and width of perturbation, the aerosol particle radius, and the altitude of the PMSE occurrence are investigated. The obtained results are useful for interpreting the experimental observations.

The acceleration of electrons by the self-generated quasi-static magnetic field in the interaction of n laser pulses with a plasma is investigated. The relativistic dynamics of a single electron is followed numerically. It is found that the electron can be much more effectively accelerated by n laser pulses, each with amplitude a0 and having a fixed frequency difference from the preceding one, than by a single pulse with amplitude na0. The large enhancement of acceleration can be attributed to stochastic-like resonance between the electron motion at the beat-frequencies of lasers and at the cyclotron motion frequency.

Introduce the measuring instrument of plumb coaxial error for long-distance orifices which is according to the measuring requests of Flange Place of experiment fast neutron reactor in nuclear power equipment and designed by combining the laser collimation technique and CCD imaging technique. The measuring instrument constructs the plumb line with utilizing the characteristic of laser and making the CDD as imaging screen, and the line is regarded as the datum line in measurement and used for measuring coaxial error of the large orifices' manufacture and assemblage under plumb state. Angle resolving power is: 0.3; displacement resolving power is: 0.02 mm; respective degree of uncertainty of measurement results are: 0.1; 0.01 mm. The paper detailed introduces the idiographic design principle and measure method of the measuring instrument, and analyzes the measure error. It is applied to measure the precision of manufacture and the coaxial error of assemblage of the large or heavy pipe casting equipment.

The effect of plasma nonuniformity on the electron energy distribution function (EEDF) and plasma parameters such as the ion density, electron temperature and dust charge in a dusty plasma are studied using a Boltzmann equation for the electrons and the fluid equations for the ions. The EEDF and the plasma parameters are obtained taking into account electron diffusion. The effect of the dusts on the electron energy-relaxation length is shown to be significant. The latter decreases as the dust density and/or size increase. Only at relatively high dust densities/sizes do the results of the homogeneous Boltzmann equation approach that of the more accurate kinetic equation.

Management of nanopowder and reactive plasma parameters in a low-pressure RF glow discharge in silane is studied. It is shown that the discharge control parameters and reactor volume can be adjusted to ensure lower abundance of nanopowders, which is one of the requirements of the plasma-assisted fabrication of low-dimensional quantum nanostructures. The results are relevant to micro- and nanomanufacturing technologies employing low-pressure glow discharge plasmas of silane-based gas mixtures.

The optical behavior of a four-level system in a ring cavity driven by two coherent laser fields is studied. One laser field is treated as the incident field and the other the control field, respectively. It is found that there is optical transparency when the difference between the two frequency detunings of the incident and control fields from the corresponding atomic transition frequencies is zero. Optical bistability can be produced and controlled by increasing the magnitude of the frequency difference. The bistable hysteresis becomes larger when the frequency difference is increased. Further increase of the latter can lead to onset of multistability.

A classical model for high-harmonic generation from the interaction of a laser pulse and an atomic gas is introduced. The effects of finite pulse width and laser magnetic field are included. The optimum intensity-pulse width relation for high-harmonic emission and the corresponding power spectrum are presented. The existing high-harmonic cutoff law is found to remain valid.

To accurately recover data encrypted in a chaotic carrier, the chaotic signals in the encoding and decoding systems must be suitably synchronized. In this paper secure communication based on similar but non-identical chaotic encoding and decoding systems is examined using the Lorenz and Lorenz-Stenflo (LS) equations for generating the chaotic signals. Since the two systems have different chaotic attractors, exact synchronization between them does not occur. However, it is shown that data encrypted in a Lorenz carrier can be accurately extracted by a LS decoder (and vice versa) if the rotation number in the LS equations is not too large. Detection of signals based on an LS chaotic electronic circuit is also investigated.

The structure of a steady-state surface-wave sustained cylindrical argon plasma is investigated theoretically by taking into account electron heat transport. The radial profiles of the plasma density, temperature, velocity, as well as the the density of the 3p56d excited-state argon atoms are calculated. The effects of different models of the electron heat flux and their boundary conditions are also investigated. The results are compared with existing experiments and theories.

Stable two-dimensional dust clusters are found by Molecular Dynamics simulation using two model interaction potentials. The clusters can be in either solid or liquid state. The results of the two models are discussed.

Turning points for transitions between the electrostatic and electromagnetic discharge modes in low-frequency (≈ 500 kHz) inductively coupled plasmas have been identified and cross-referenced using time-resolved measurements of the plasma optical emission intensities, RF coil current, and ion saturation current collected by a single RF-compensated Langmuir probe. This enables one to monitor the variation of the plasma parameters, power transfer efficiency, which accompany the discharge hysteresis. The excitation conditions for the pure and hybrid modes in the plasma are considered, and the possibility of the TMmnl → TEm'n'l' transitions at higher frequencies are discussed.

The theory of very low frequency dust acoustic waves in weakly coupled collisional plasmas with variable-charge dusts is extended to that containing strongly coupled dusts. The strong dust coupling is described by a viscoelastic relaxation model with a wavevector-dependent relaxation time. Dust-charge variation, collisional dissipation, ionization and recombination, often on the same time scale, are included. A generalized dispersion relation is obtained and relevant limiting cases are analyzed. It is found that the dissipative longitudinal modes are strongly affected by the dust coupling.

The stair-like structure in the correlation integral of measured data is investigated. It is shown that the stairs are caused by the limited floating-point accuracy of the data in the measurement, and are completely different from the noise in the measured phenomenon. It is found that a modified singular value decomposition filter with very large projection dimension can improve the precision of the data and smooth the stairs in the correlation integral.

Several secure data encryption methods based on synchronized chaotic carrier systems are proposed. It is shown that data signals can be securely and efficiently encoded using physical chaotic systems as carriers. Robustness and signal recover in high-dimensional encoding systems are investigated.

The implosion dynamics of a high-density fibre plasma driven by a spinning Z-pinch is investigated. Spin coupling with the inner fibre plasma is taken into consideration. Numerical results show that the coupling can affect the plasma dynamics and reduce the maximum achievable density and temperature. Thus the large spin needed to prevent the Rayleigh-Taylor instability can adversely affect fusion conditions. For intermediate spin and coupling, high densities and temperatures can be realized for fibres seeded with high-Z impurities.

A condition associated with the plasma boundary or other charged interface is reviewed. It is pointed out that in comparing theories and simulations of such interfaces, in order to avoid conflicting results it should be ascertained that the systems under consideration are thermodynamically equivalent. For the plasma–wall interface in equilibrium, the rate of change of the surface-charge density with respect to the surface potential must be positive.

A graphical overview of the bifurcation characteristics of the generalized Lorenz equations obtained by Stenflo (1996 Physica Scripta 53 83) for nonlinear acoustic gravity waves in a rotational system is presented.

The clustering process of charged grains often resembles a formation stage of colloidal and spongy matter, as well as some astrophysical objects. In this paper, molecular dynamics simulation is used to simulate the formation process of clusters of massive charged grains in plasmas. It is found that, from an initially uniform distribution of grains with Maxwellian velocity distribution, a statistically stationary system of clusters, each with different dynamic as well as thermodynamic characteristics, can form. The dependence of the asymptotic, of the final, state of the cluster system on the initial temperature and density of the grains is discussed.

A new class of exact solutions of the Vlasov-Poisson equations based on the Jeans theorem is considered. The self-consistent solutions for the evolution of the system from given initial particle di ...

The mechanisms of energy/momentum exchange in rotating and compressing plasma flows have been discussed. It has been shown that such flows are capable of transforming the energy of different degrees of freedom into the energy of one degree owing to the interaction of the coupled nonlinear radial, axial and azimuthal electron-ion oscillations. These processes may lead to the additional acceleration of the flow in azimuthal or axial direction so they might be instrumental for the creation of space thrusters employing pulse transformations for propulsion.

Generation of ultra-short betatron x-rays by laser-accelerated electron beams is of great research interest as it has many applications. In this paper, we propose a scheme for obtaining bright betatron x-rays by applying external wiggler magnetic field in the laser wakefield to resonantly drive the betatron oscillations of the accelerated electrons therein. This results in a significant enhancement of the betatron oscillation amplitude and generation of bright x-rays with high photon energy. The scheme is demonstrated using two-dimensional particle-in-cell simulation and discussed using a simple analytical model.

Evolution of a non-neutral cold electron–positron plasma slab is investigated. Initially the slab consists of a quasineutral plasma core bounded on both sides by layers containing only positrons (or electrons). Results from a nonperturbative, or mathematically exact, analysis of the governing fluid conservation equations and the Poisson equation show that despite their equal mass and charge magnitude, the electron and positron fronts can expand separately as well as a single fluid, and that nonlinear surface oscillations can be excited on the expansion fronts.

Nonlinear Alfven wave trains in resistive and viscous magnetohydrodynamics plasmas are investigated. In weakly dissipative one-dimensional systems the inclusion of these effects leads to dissipative damping of Alfven waves and heating of the plasma. It is found that plasma flow along the background magnetic field can reduce/increase the visco-resistive damping when the flow is along/against the Alfven wave. In strongly dissipative systems, the front of the Alfven wave train damps slower than the others, and it gradually forms a damping soliton. In two-dimensional systems, Alfven wave phase mixing induced by inhomogeneity of the background plasma leads to enhancement of the dissipative damping and the corresponding plasma heating.

The behavior of nonlinear Alfven waves propagating in ideal MHD plasmas is investigated numerically. It is found that in a one-dimensional weakly nonlinear system an Alfven wave train can excite two longitudinal disturbances, namely an acoustic wave and a ponderomotively driven disturbance, which behave differently for and , where β is the ratio of plasma-to-magnetic pressures. In a strongly nonlinear system, the Alfven wave train is modulated and can steepen to form shocks, leading to significant dissipation due to appearance of current sheets at magnetic-pressure minima. For periodic boundary condition, we find that the Alfven wave transfers its energy to the plasma and heats it during the shock formation. In two-dimensional systems, fast magneto-acoustic wave generation due to Alfven wave phase mixing is considered. It is found that the process depends on the amplitude and frequency of the Alfven waves, as well as their speed gradients and the pressure of the background plasma.

The degenerate microwave (including both two- and four-wave) mixing in a dusty plasma is studied on a slow time scale which involves heavy impurity particle response to the electromagnetic waves. It is shown that the density grating and the corresponding third-order nonlinear susceptibility are independent of the wavelength of the grating, and decrease almost linearly with the concentration of the dust particle. The two-wave mixing process does not contribute to the phase-conjugate reflectivity, it introduces only an additional wavenumber shift to the electromagnetic waves.

It is demonstrated how nonlinear surface modes at the boundary of a cylindrical electronic medium are coupled to external constant or time-varying electric fields in the bounding dielectric. Exact equations governing the interaction are obtained and investigated numerically. It is found that the external field can drive only certain surface modes, in spite of the fact that all the modes are strongly coupled.

The evolution of resonant waves due to the nonlinear interaction associated with the plasma-maser effect is considered, and the nonlinear growth rate obtained. It is shown that the latter contains a "polarization" (only for the resonant waves) as well as a "direct third-order" contribution. In particular, the effect of the plasma-maser mechanism on the beam instability caused by Landau growth is investigated. It is shown that this effect can significantly modify the behavior of the instability. The conditions for the dominance of the plasma-maser effect nonlinearity over that of the usual quasilinear mechanism are given.

A relatively self-consistent theory of dust-acoustic waves in the strongly coupled dusty plasmas containing variable-charge impurities is given. Relevant physical processes such as dust elastic relaxation and dust charge relaxation are taken into account. It is shown that the negative dispersion of dust-acoustic waves due to the strong correlation of dusts is enhanced in the presence of dust-neutral collisions.

The nonlinear interaction of powerful short electromagnetic pulses with a plasma consisting of two groups of electrons and immobile ions has been studied. It is shown that the interaction is governed by a nonlinear equation for the electromagnetic wave envelope and a driven nonlinear equation for the low-frequency electron fluctuations. The driver for the latter depends explicitly on the spatio-temporal evolution of the electromagnetic wave flux. Depending on the cold-to-hot electron density ratio, the localized pulse can propagate with sub- as well as supersonic velocities accompanied by compressional or rarefactional density perturbations. The conditions of existence for the different types of solitary pulses are obtained. The present investigation may be relevant to the study of wave-plasma interaction devices such as inertial fusion confinement as well as to ionospheric modification experiments.

The three-dimensional far-field electrostatic potential of two co-moving point charges are considered. In contrast to the one-dimensional nonlinear case, it is found that the shielding behavior remains similar to that of a single moving charge.

Feedback control of collapse-induced turbulent condensation in a dissipative open Langmuir wave system governed by a two-dimensional generalized nonlinear Schrodinger equation is investigated numerically by following the evolution of an initial disturbance. It is found that with self-regulated feedback control the wavelength of the asymptotic turbulent condensate can, to a certain degree, be controlled.

The formation and properties of stable charged-grain clusters are followed using molecular dynamics simulation. It is found that uniformly distributed grains with random velocities can form clusters of different thermodynamic states within the same system. The formation process and the dependence of the number and types of clusters in the statistically asymptotic state of the system on the initial grain temperature and density are investigated.

A new scheme of radiation pressure acceleration for generating high-quality protons by using two overlapping-parallel laser pulses is proposed. Particle-in-cell simulation shows that the overlapping of two pulses with identical Gaussian profiles in space and trapezoidal profiles in the time domain can result in a composite light pulse with a spatial profile suitable for stable acceleration of protons to high energies. At ~2.46 × 1021 W/cm2 intensity of the combination light pulse, a quasi-monoenergetic proton beam with peak energy ~200 MeV/nucleon, energy spread

The periodic and chaotic solutions of the generalized Lorenz equations obtained by Stenflo (1996 Physica Scripta 53 83) are investigated. It is shown that for the parameters chosen, both periodic and chaotic solutions exist.

Exact wave solutions are constructed for a cylindrical cold plasma bounded by a dielectric, taking into account possible particle sources. It is shown that the volume waves can either be amplified or damped because of their density dependence, while the surface waves are unaffected by the source.

Fully nonlinear very low frequency dust acoustic solitary waves in a magnetized impurity-containing plasma are investigated.

Excitation of intense periodic single-cycle light pulses in a stochastic background arising from continuous wave stimulated Brillouin scattering (SBS) in a long optical fiber with weak optical feedback is found experimentally and modeled theoretically. Such intense light-pulse chains occur randomly and the optical feedback is a requirement for their excitation. The probability of these forms, among the large number of experimental output signals with identifiable waveforms, appearing is only about 3%, with the remainder exhibiting regular SBS characteristics. It is also found that pulses with low period numbers appear more frequently and the probability distribution for their occurrence in terms of the pulse power is roughly L-shaped, like that for rogue waves. The results from a three-wave-coupling model for SBS including feedback phase control agree well qualitatively with the observed phenomena.