An analysis of relativistic electron trajectories in a free-electron laser with a helical magnetic wiggler and an ion channel is presented. The wiggler field amplitude and the ion number density are taken to be uniform. Also included are the self-electric and self-magnetic fields of the electron beam, which is assumed to be of constant velocity and electron number density. The Hamiltonian, which is a constant of the motion, is first expressed in cartesian coordinates and momenta. A second constant of the motion is obtained by canonical transformation. The steady-state orbits, Poincaré maps, and Liapunov exponents are employed to investigate the chaotic motion in the presence of the ion channel. Numerical calculations reveal conditions under which chaotic and non-chaotic orbits exist.

It is shown that the ponderomotive force of magnetic-field aligned circularly polarized electromagnetic waves can create space charge electric fields in a magnetized electron–positron–ion plasma. The space charge electric fields can, in turn, accelerate ions. Possible applications to the origin of energetic ions in laboratory plasmas and astrophysical settings are discussed.

The existence of large-amplitude dust-acoustic double layers is investigated in an unmagnetized dusty plasma comprising a negatively charged warm dust fluid, non-thermal ions and Boltzmann electrons. It is found that the non-thermal plasma supports the existence of rarefactive double layers only. The dependence of the double-layer amplitude and Mach number on various parameters such as the non-thermal parameter, dust temperature and electron concentration is numerically examined.

Stationary magnetohydrodynamic (MHD) flows with a symmetry are analyzed for very-low-density plasmas in strong magnetic fields, in the infinite conductivity limit. In this particular case the simplified form of Ohm's law usually employed in the ideal MHD case is no longer valid, because Hall's and electron pressure terms in the generalized Ohm's law must be retained. Thus we include them in our equations. The assumption of symmetry makes possible the definition of an ignorable coordinate and of current functions for the divergence free magnitudes. In the case without Hall's effect and electron pressure terms in Ohm's law, there is only one independent current function; in the present case, instead, two Stokes functions are independent. We choose the current function of the magnetic induction field and that of the plasma flux, $\psi$ and $\chi$, to be independent. Then we can express the other Stokes functions of our problem as functions of $\psi$ and $\chi$. We assume helical symmetry, as it is the most general form of spatial symmetry and impose incompressibility, that is ${\bf v\cdot\nabla\rho =}\,0$. We obtain a system of two differential equations for $\psi$ and $\chi$, and solve them for the particular case of constant density. Then we calculate the limit of our solution for Hall's effect that tends to zero, in order to make a comparison with the results obtained for the case without Hall's effect. Finally, we find the necessary conditions to obtain confined plasma columns embedded in a force-free plasma or in a vacuum.

The two-dimensional dynamics of nonlinear ion-acoustic waves in a weakly magnetized plasma comprising cold ions and trapped as well as free electrons is considered. It is shown that owing to departure from the Boltzmann electron distribution to a vortex-like one, the dynamics of small but finite-amplitude ion-acoustic waves is governed by a new nonlinear equation which is valid for both unmagnetized and magnetized plasmas. For exactly vanishing magnetic fields the modified Kadomtsev–Petviashvili (mKP) equation is recovered. For weak magnetic fields, however, the dynamics is mainly different from the mKP equation, depending on the amplitude. By increasing the magnetic field, the new equation becomes similar (but not identical) to the modified Zakharov–Kuznetsov (mZK) equation, which is fulfilled for very strong magnetic fields. The plane periodic and solitary wave solutions of this equation are obtained using the appropriate scalings.

An analysis of self-fields associated with charge and current densities of the electron beam in a free-electron laser with helical wiggler and axial magnetic field is presented. The self-electric field is derived from Poisson's equation. A more detailed analytical model for the self-magnetic field is determined from Ampere's law. Mutual influence of the electron velocity and self-magnetic field is considered to account for the total self-magnetic field. It is shown that for group I orbits, the self-magnetic field acts as a diamagnetic correction to the wiggler magnetic field; for group II orbits, it acts as a paramagnetic correction. Both diamagnetic and paramagnetic effects become stronger near the transverse velocity resonance. An important effect of the self-fields on the electron trajectories is the creation of unstable orbits for group II, which are not found in the absence of self-fields.

We describe a general multi-scale method to model hydrogen isotope transport, over length scales from angstroms to centimeters and time scales from picoseconds to several seconds, in a complex three-dimensional porous geometry using molecular dynamics, kinetic Monte Carlo and Monte Carlo diffusion simulations. We present comparisons with experimental results for hydrogen diffusion and hydrogen atom desorption from graphite. Finally, we demonstrate the flexibility of the computational tools used to tackle problems at different scales.

The unstable plasma sheath resonance in a pulsed low-pressure hollow-cathode discharge was found to occur when the Bohm criterion fails. This happens during the transition of the discharge to a steady state. The duration of this transition is determined by the time required for the ion sound to cross the plasma volume. During this time a strong radio-frequency (RF) component may appear in the discharge current due to the instability of the plasma sheath near the cathode. The frequency of the RF oscillations is associated with the ion plasma frequency. The conditions required for the instability of the plasma sheath were investigated. We suggest a theoretical model which extends our earlier theory and explains the existing experimental results. The model also predicts a certain shift in the resonance frequency during the pulse, which was indeed discovered experimentally.

The aim of this paper is to analyze the propagation of large-amplitude Alfvén waves in a perfectly conducting plasma in the magnetohydrodynamic approximation, for cylindrical magnetic tubes. In a similar way to that done in Sallago and Platzeck, instead of linearizing the magnetohydrodynamic equations and searching monochromatic waves, we impose the conditions that the perturbations propagate without distortion with a group velocity parallel to the background magnetic induction field, in the reference system in which the plasma is locally at rest, the perturbations are incompressible, there exists a relation between the velocity and induction magnetic field perturbations, and the total pressure remains constant. The solutions are similar to the case in which the background fields vary with a rectilinear variable. When the solution is searched using this methodology there is no singularity problem. If the background total pressure is not uniform and constant, it is not possible to find waves of large amplitude that propagate like Alfvén waves in cylindrical magnetic tubes.

From the width of the emitted 656.3 nm Balmer $\alpha$ line, it was found that low-pressure (0.5 torr) capacitively coupled radio-frequency (RF) ${\rm He}/{\rm H}_2$ (95/5%) as well as ${\rm Ar}/{\rm H}_2$ (95/5%) plasmas showed excess broadening throughout the volume (13.5 cm ID $\times$ 38 cm length) of a General Electronics Conference (GEC)-type cell; not merely in the vicinity of the electrodes of ${\rm Ar}/{\rm H}_2$ plasmas as reported by several groups. About 50% of the hydrogen of the ${\rm He}/{\rm H}_2$ was ‘hot’ with an average hydrogen atom energy of 40–50 eV, compared to $\sim$1 eV for pure hydrogen, whereas ${\rm Ar}/{\rm H}_2$ showed a single fast or ‘hot’ 40–50 eV population. The broadening was undiminished at 15 cm from the powered electrode, independent of power over a substantial range, but dependent on the hydrogen concentration. In contrast to the atomic hydrogen lines, no broadening was observed in helium or argon lines. Also, in ‘control’ ${\rm Xe}/{\rm H}_2$ plasmas run in the same cell at similar pressures and absorbed power, no significant broadening of atomic hydrogen, ${\rm Xe}$, or any other lines was observed. Stark broadening or acceleration of charged species due to high electric fields cannot explain the results since: (i) the electron density was insufficient by orders of magnitude, (ii) the RF field was essentially confined to the cathode fall region in contrast to the broadening that was independent of position, and (iii) only the atomic hydrogen lines were broadened. Rather, the data are consistent with a model wherein ${\rm He}^+$ and ${\rm Ar}^+$ act catalytically through a resonant energy transfer mechanism to create ‘hot’ hydrogen atoms in plasmas.

Most of the mode conversion theories considered so far assume only a plane-layered medium, i.e. a medium where the parameters depend on one spatial coordinate. We generalize the mode-conversion method of Cairns and Lashmore-Davies to plasmas with two-dimensional inhomogeneities. In the method presented here, the frequencies $\omega_1$ and $\omega_2$ of the uncoupled modes belonging to two different dispersion equations are considered as functions of the space variable $\mathbf r$ and the wave vector $\mathbf k$ and are coupled together via a small quantity $\eta$. We calculate the energy transmission and conversion coefficients analytically by solving two coupled wave amplitude equations in the electron cyclotron range of frequencies. The results are applicable to electron Bernstein wave heating of plasmas with two-dimensional inhomogeneity, e.g. spherical tokamaks.

We present a three-dimensional analysis covering an investigation of the behavior of the magnetosheath plasma velocity and the magnetic field during the transfer from the magnetosheath to the magnetosphere. Magnetic reconnection is assumed to occur at an arbitrary line parallel to the $y$-axis, located in a region along the magnetopause stretching from the sub-solar point to the north. We do not focus on the process itself, but on its implications for the plasma flow and the magnetic field outside the diffusion region. Viscosity and resistivity are included in the magnetohydrodynamic equation of motion as non-ideal effects. The governing equations are solved approximately using the method of asymptotic expansions, with expansion in orders of large Reynolds and Lundquist numbers. We present two classes of solutions describing the properties north and south of the reconnection line, respectively. Results are presented for two locations of the reconnection line at distances of two and seven Earth radii from the sub-solar point correspondingly. It is shown that the velocity increases faster north of the reconnection line, and that the effect intensifies as the location of the reconnection line moves further away from the sub-solar point. It is also shown for this case, that there is less variation of the magnetic field and an increase in the field strength.

The stable conditions and gravitational effects on the surface dust-acoustic wave are investigated in self-gravitating semi-bounded dusty plasmas. The dispersion relation of the surface dust-acoustic wave is obtained by the plasma dielectric function with the specular reflection boundary condition. It is shown that the surface dust-acoustic wave become unstable for any values of the wave number when $\tfrac{1}{2}\leq (\omega_{\rm J}/\omega_{\rm pd})^2\leq 1$. However, when $(\omega_{\rm J}/\omega_{\rm pd})^2 > 1$ or $(\omega_{\rm J}/\omega_{\rm pd})^2 < \tfrac{1}{2}$, the Jeans instability does not occur for the domain of the wave number $k_z \lambda_{\rm D} > (\omega_{\rm J}/\omega_{\rm pd})|[(\omega_{\rm J}/\omega_{\rm pd})^2 - 1]/[2(\omega_{\rm J}/\omega_{\rm pd})^2 - 1]|^{1/2}$. It is also found that the phase velocity of the surface wave decreases with increasing Jeans frequency.

Hydrogen adsorption by graphite is examined by classical molecular dynamics simulation using a modified Brenner reactive empirical bond order (REBO) potential. Such interactions are typical in chemical sputtering experiments, and knowledge of the fundamental behavior of hydrogen and graphene in collisional conditions is essential for modeling the sputtering mechanism. The hydrogen adsorption rate is found to be dependent on the incident hydrogen energy and not on graphene temperature. Rather than destroying the graphene, hydrogen incidence at energies of less than 100 eV can be classified into three regimes of adsorption, reflection and penetration through one or more graphene layers. Incidence at the lowest energies is shown to distort the graphene structure.

Neutron production from a thin deuterium–tritium (D–T) foil irradiated by two intense femtosecond laser pulses from opposite sides with zero phase difference is studied analytically and numerically. For the interaction of a laser pulse of amplitude $a=7$, focal area 100 $\mu$m$^2$ and areal density $4.4\times 10^{18}$ cm$^{-2}$ with a D–T plasma foil, about $1.17\times 10^{21}$ neutron s$^{-1}$ can be obtained, much more than from other methods. The profiles of the ion and electron densities are also calculated.

In the present analysis we study the self-consistent propagation of nonlinear electromagnetic pulses in a one-dimensional relativistic electron–ion plasma, from the perspective of nonlinear dynamics. We show how a series of Hamiltonian bifurcations give rise to the electric fields which are of relevance in the subject of particle acceleration. Connections between these bifurcated solutions and the results of earlier analysis are made.

The present paper examines several models of turbulent transport in which the use of the Corrsin conjecture is effective. We discuss applying the diffusive approximation of correlation effects for a scaling description of turbulent transport in a system of random drift flows. The renormalization method of quasi-linear equations to treat the diffusion of magnetic force lines is considered. The factorization applied by Corrsin makes it possible to obtain transport estimates on the basis of power approximations of the spatial correlation function. The diffusive approximation of correlation effects is effectively used in percolation and fractal models of anomalous transport. We point out the close relation among the Corrsin conjecture, renormalized quasi-linear equations and scaling estimates in which the characteristic spatial scale also appears to be the diffusive displacement. In the present paper we focus on scaling arguments that play an important role in obtaining the estimates of transport effects.

The free energy associated with the relative streaming of plasma and dust particles can feed streaming instabilities. Here we consider the case of an unmagnetized plasma and use the results of kinetic theory which consistently take into account the plasma particles–dust collisions and dust charge fluctuations. These are valid in the parameter regime where the plasma particles–dust collisions dominate with respect to the binary plasma collisions.

A three-dimentional particle–particle particle–mesh (P3M) model for dusty plasma has been developed. The model implies a fully kinetic description for all species in the plasma, being able to resolve the finite size effects for dust grains. The model was used for simulation of charging process for the dust grains in a capacitive radiofrequency discharge.

In the Lorentz–Vlasov model of a plasma the ions are assumed to be fixed in space with disordered distribution, and the Coulomb interaction between electrons is approximated by the Vlasov field, calculated self-consistently from the electron position–momentum distribution function. If correlations between ions are neglected, then the dynamical conductivity of the plasma may be evaluated from the dynamics of the electron gas in interaction with a single ion, the remaining ions being approximated by a uniform background. In dielectric or energy-loss theory, the dynamical friction coefficient is expressed in terms of the dielectric function of the uniform electron gas. A more detailed theory must take full account of the scattering of electrons by the selected ion. It is shown for an electron gas at zero temperature and metallic density, and for a simple ion pseudopotential, that the frequency dependence of the friction coefficient differs appreciably from that predicted by energy-loss theory.