An effect of drift is investigated on the segregation pattern in diffusion-limited aggregation (DLA) with two components (A and B species). The sticking probability ${\mathit{P}}_{\mathit{A}\mathit{B}}$ (=${\mathit{P}}_{\mathit{B}\mathit{A}}$) between the different species is introduced into the DLA model with drift, where the sticking probability ${\mathit{P}}_{\mathit{A}\mathit{A}}$ (=${\mathit{P}}_{\mathit{B}\mathit{B}}$) between the same species equals 1. By using computer simulation it is found that the drift has an important effect on not only the morphology but also the segregation pattern. Under the drift and the small sticking probability, a characteristic pattern appears where elongated clusters of A species and of B species are periodically dispersed. The period decreases with increasing drift. The periodic structure of the deposits is characterized by an autocorrelation function. The shape of the cluster consisting of only A species (or B species) shows a vertically elongated filamentlike structure. Each cluster becomes vertically longer with decreasing sticking probability ${\mathit{P}}_{\mathit{A}\mathit{B}}$. The segregation pattern is distinctly different from that with no drift and a small sticking probability ${\mathit{P}}_{\mathit{A}\mathit{A}}$. The effect of the concentration on the segregation pattern is also shown.

We study interfacial dynamics far from equilibrium in models with nonlocal shadowing effects in two spatial dimensions. Results from a nonequilibrium solid-on-solid model and a nonlinear, nonlocal partial-differential equation describing the time evolution of an interface are presented. In a wide temperature range, the systems form columnar structures that coarsen according to a power law. The coarsening exponents are measured in both models. The power spectrum of the interface shape exhibits a dynamic scaling. At low temperatures the system is described by the equation of Kardar, Parisi, and Zhang [Phys. Rev. Lett. 56, 889 (1986)]. We discuss the dynamic universality, and present evidence for a nonequilibrium phase transition between a rough and a columnar phase for the solid-on-solid model.

The enhancement of the fusion reaction rate in high-density two-component plasmas that consist of deuterium (D) and high-Z material such as carbon (C) or titanium (Ti) has been investigated theoretically. Ion-ion correlation in high-density two-component plasmas is described by a hypernetted-chain (HNC) equation including Coulomb potential of bound electrons. To take into account the effects of bound electrons, we calculate the degree of ionization of atoms consistently with HNC equations by using the Thomas-Fermi model. The results show that the fusion reaction rate of the D-D interaction is enhanced by a factor from 2 to 4 because the strong screening by the surrounding high-Z ions reduces an effective potential between two colliding deuteriums, and then the degree of ionization of high-Z materials is found to be important to determine the enhancement factors.

Wave-energy absorption of a plasma due to cyclotron harmonic resonance is evaluated analytically and by a simulation. The static magnetic field is characterized with B⋅∇B=0, and a longitudinal wave is supposed to propagate across the magnetic field. In the calculation an orbit modification of the cyclotron motion of particles is taken into account. It is found that the absorption for the fundamental harmonic resonance (m=1) is depressed from that of the conventional linear theory while the absorptions for m≥2 are enhanced, where m is the harmonic number. The enhancement is significant when k${\mathrm{\rho }}_{\mathit{t}}$≪1 (k the perpendicular wave number and ${\mathrm{\rho }}_{\mathit{t}}$ the gyroradius of the thermal particle) and when the interaction time between the plasma particles and the wave exceeds a critical value that is obtainable analytically. For all m and k${\mathrm{\rho }}_{\mathit{t}}$, there appear peaks or saturations in the time evolution of the absorbed energy.

We report on the wavelengths and satellite intensity factors for selected heliumlike ions undergoing dielectronic recombination via several higher-lying resonance states, viz., the 1${\mathit{s}}^2$ε${\mathit{l}}_{\mathit{c}}$→1s2lnl’→1${\mathit{s}}^2$ml’’ with n=5, 6, 7, and 8. The calculations have been performed in the intermediate-coupling scheme using the multiconfiguration Hartree-Fock atomic model.

The power flow in rapid magnetization or demagnetization of a plasma that conducts current between two cylindrical conductors is analyzed through a consideration of the necessarily two-dimensional physics. This fast Hall-field-dominated evolution of the magnetic field must be accompanied by a large dissipation of power, partly in the bulk of the plasma and partly at the electrodes. Interestingly, precise statements can be made about this partitioning of the power.

Percolation theory in conjunction with a cylindrically symmetric Thomas-Fermi model is introduced to calculate the ionization potential lowering in hot and dense plasmas. The bound-electron level shifts due to the interaction with the nearest neighbor are calculated by means of a cylindrically symmetric model. The critical energy for which a negative-energy electron wave function overlaps a macroscopic portion of the plasma is then computed by percolation-theory methods.

We identify mechanisms for particle transport across a cross-field sheath. We present a study of E×B drift motion in a vortex in which the ion drifts are perturbed by their finite gyroradii and electron drifts are perturbed by one or more traveling waves. Large-scale vortices, which are the result of nonlinear saturation of the Kelvin-Helmholtz instability resulting from shear in the E×B drift velocity, have been observed in plasma simulations of the cross-field sheath [K. Theilhaber and C. K. Birdsall, Phys. Rev. Lett. 62, 772 (1989); Phys. Fluids B 1, 2241 (1989); 1, 2260 (1989)]. Small-scale turbulence is also present, and ions and electrons are transported across the sheath. A vortex alone does not allow for the observed electron transport because the electron drift orbits simply circulate. On the other hand, the ion motion can be stochastic from resonant interaction between harmonics of the drift motion and the gyromotion, independent of the background turbulence. The fluctuations in the ion density would then give rise to a small-amplitude wave spectrum. The combined action of the vortex fields and traveling-wave fields on the electron motion can then lead to stochastic electron diffusion. We study these effects, showing that the values of vortex fields observed in the simulation are sufficient to lead to both ion and electron stochasticity. Furthermore, the rate of the resulting diffusion is sufficient to account for the diffusion observed in the simulation.

The propagation of hydromagnetic waves is considered in the approximation of geometrical optics. The variation of wave amplitudes in space and time is determined from the energy balance—in contrast to the usual WKB procedure. While Alfvén waves are unaffected by the equilibrium pressure gradient, we find a gradient-driven instability of outgoing fast and ingoing slow magnetosonic waves due to diffraction or self-interaction. The corresponding wave vectors are in the range 1/a<k<1/ √${\mathit{L}}_{\mathit{c}}$a , where a is the inhomogeneity scale perpendicular to the magnetic field and ${\mathit{L}}_{\mathit{c}}$≊η/β${\mathit{v}}_{\mathit{A}}$ for the fast magnetosonic waves.

The problem of hydromagnetic disturbances in an unbounded, ideal fluid of finite electrical conductivity due to the sudden introduction of a magnetic dipole, placed parallel to homogeneous excitation field ${\mathbf{H}}_0$, has been discussed. Asymptotic solutions for the perturbations h of ${\mathbf{H}}_0$ have been obtained for both large and short times. Figures representing components of the disturbed field h for different values of time are presented.

A steady-state model is used to calculate the ionization balance for a selenium plasma at electron temperatures where the Ne-like stage is dominant. In this model, the ion distribution and free-electron density are calculated for a specified particle density and temperature. In addition, each state of a given ion is connected to appropriate states of the same ion by excitation and deexcitation and connected to the appropriate states of adjacent ions by ionization and recombination. Excited states including autoionizing states are treated explicitly. Rate coefficients for all processes are based consistently on atomic-structure calculations. The calculations indicate that hundreds of electron configurations are necessary to obtain suitable results and that electron configurations must be included consistently across ion stages. Autoionizing states are shown to be the major influence in determining the ionization balance. The use of plane-wave Born collision strengths instead of better distorted-wave collision strengths appears to have a negligible effect on the overall ion stage distribution at moderate densities. The results may explain why F-like lasing transitions were not observed in the experiments by Matthews et al. [Phys. Rev. Lett. 54, 110 (1985)].

The propagation of a radiation heat wave through a thin foil of solid gold was investigated experimentally. The wave is driven by the intense thermal radiation in 1–3-mm-diam gold cavities heated by an intense laser pulse (duration 0.8–0.9 ns, wavelength 0.35 μm) to temperatures ranging from 80 to 240 eV. Evidence of the propagating wave was obtained from the delayed onset of thermal emission from the outer side of the foil. A detailed comparison of the results with the self-similar solution for the ablative heat wave and with numerical simulations is presented.

Comparisons of experimentally measured transport properties with values determined from calculations based on three-temperature-kinetic theory, on bi-Maxwellian kinetic theory, and on Monte Carlo simulations have established that the ${\mathrm{Na}}^{+}$-Ne interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] is a close approximation to the true potential. (In the bi-Maxwellian approach, the ions are modeled in first-approximation as a large fraction that behaves according to a low-temperature Maxwell distribution and a small fraction that follows one of higher temperature; the true distribution is computed from these by a weighted-residual method.) This potential was then used to compute velocity distribution functions of ${\mathrm{Na}}^{+}$ ions in room-temperature Ne at widely different average ion energies. The skewness of the distributions in the direction of the electric field initially increased rapidly with increasing energy, and then slowly decreased, as did the excess kurtosis both parallel and perpendicular to the electric-field direction. It was clearly established that there is correlation between the perpendicular and parallel velocity-component distribution functions and that the correlation increases with increasing average ion energy.

Line profiles of hydrogenlike B v Lyman-series lines and B v ${\mathrm{H}}_{\mathrm{\alpha }}$ were measured in a laser-produced plasma. The lines were measured using a microchannel-plate detector system. The measured Stark width of ${\mathrm{L}}_{\mathrm{\delta }}$ is used to determine the electron density in the plasma. This electron density is used to compare measured ${\mathrm{H}}_{\mathrm{\alpha }}$ linewidths with a theoretical extrapolation of calculations for C vi. A scaling formula is proposed for Stark widths of higher members of the isoelectric sequence at high densities as required for efficient short-wavelength recombination lasers.

The behavior of excess electrons in neon gas in a wide range of densities is investigated using molecular-dynamics simulations with a parameter-free interparticle potential. A realistic pseudopotential reproducing the measured electron-Ne low-energy scattering properties is used. A transition from quasifree behavior to a localized regime where the electron is trapped in a bubblelike cavity is observed as the density is increased beyond a value that is close to the experimental one. The calculated electron mobilities in a wide range of densities are also found to be in reasonable agreement with the experimental data.

In this paper we discuss the theory of emission by relativistic electrons in linearly polarized undulators. We show that the analytical computations are greatly simplified by the introduction of the so-called generalized Bessel functions, originally introduced to treat problems for which the dipolar approximation does not hold. We also discuss the modification induced in the brightness by the inclusion of the sextupolar terms, which arise when electrons are injected off the undulator axis. We show that the phenomonology inherent to this problem is very rich, as additional harmonics come into play and may cause sizable effects. The analysis we develop may be useful to obtain further insight in the physics underlying the so-called inhomogeneously broadened regime. Finally, we also discuss the inclusion of energy corrections up to 1/${\gamma }^3$ and the relevant physical consequences.

Nonlinear beam-dynamics calculations are described that account for space-charge and image-charge effects. The calculation technique is explained and, as an illustration, is applied to two elements in an intense beam-combining funnel: an rf rebuncher and an rf deflector. For the case of the rebuncher, the calculations make use of the cylindrical symmetry of the device. For the deflector, both two-dimensional and three-dimensional calculations are performed. Emittance growth is analyzed for both the rebuncher and the deflector. For the rebuncher, a technique is proposed that considerably reduces the emittance growth.

It is shown that the self-consistent interaction between wake fields and the driving electron bunch in a collisionless, unmagnetized, overdense (${\mathit{n}}_{\mathit{p}}$≫${\mathit{n}}_{\mathit{b}}$) plasma is governed by three coupled equations. In the long-beam limit, they reduce to a pair consisting of an appropriate nonlinear Schrödinger equation for the a/Ibeam wave function Ψ, and an equation for the wake-field potential that is driven by the transverse profile of the beam density, which is proportional to ‖Ψ${\mathrm{\Vert }}^2$. The pair of equations are suitable for studying the beam self-focusing (self-pinching equilibrium) for the case in which the beam-spot size is larger (smaller) than the wavelength of the wake fields. It is demonstrated that our self-consistent theory, which is based on the recently proposed thermal wave model for relativistic charged-particle beam propagation, is capable of reproducing the main results for the beam-filamentation threshold and the self-pinching equilibrium condition that are already known in the conventional theory of the beam self-interaction in collisionless plasmas.

By analytical and numerical investigation of a one-dimensional time-dependent model of a free-electron laser with a tapered wiggler we show that high efficiency can be achieved simultaneously with the suppression of the sideband instability which is triggered by the shot noise in the electron beam. The output spectrum is calculated for various degrees of tapering.

In this paper, we have obtained the power expression of the coherent harmonic emissions generated by fundamental mode bunching and explained their temporal profile and linewidth.