The sources for continuum emission are investigated in the visible wavelength range for a high-pressure argon plasma as well as for a high-pressure argon–mercury plasma used for light application. The mechanisms responsible for the continuum emission depend differently on the pressure, the temperature and the ionization degree. By changing these conditions it is shown that one can modify the dominant continuum radiation mechanism.

Operational improvement of the high-pressure argon–mercury test lamp are considered with respect to the continuum spectrum in the visible wavelength range.

The dispersion properties of low-frequency electromagnetic waves in a partially ionized multi-ion dusty magnetoplasma containing electrons, ions of two different species, charged dust particles and neutrals have been investigated. It has been found that the combined effects of stationary charged dust particles and an additional ion component introduce a new cut-off frequency, and that the polarities of dust particles and the second ion-species significantly modify this new as well as the existing forbidden frequency bands. It has also been observed that the collisions of lighter ion species significantly reduce or completely eliminate both the new and existing forbidden frequency bands, while those of heavier ions reduce or completely eliminate the new forbidden frequency band, but enhance the existing forbidden frequency band.

We present a study of a collision-less plasma governed by the Vlasov–Poisson system of equations in one space and one velocity dimension; the plasma is subject to initial density perturbations and to both periodic and non-periodic space boundary conditions. For sufficiently large values of the perturbation's amplitude and sufficiently small values of the Landau damping rate, we observe the development of two streets of phase-space holes each consisting of two counter-streaming families of holes. The two streets move in the phase space at different speeds and they may consist of a different number of holes. The fast moving street develops faster when periodic boundary conditions are used, but it appears to be more prominent and robust under non-periodic boundary conditions. In two instances, the distribution function decays within the slow moving street; it remains unaffected within the fast moving street, but it has much smaller values there.

The effect of Raman instabilities on the production of fast electrons in laser–plasma interaction has been investigated for laser intensities well above the electron trapping threshold. The results of one-dimensional particle-in-cell simulations show that in this regime the presence of Raman backscattering (RBS) hampers fast-electron production, and that its suppression increases the yield of high-energy electrons ($>$15 MeV). Such suppression has been realized either through deletion of all backscattered radiation from the simulations or through direct stimulation of Raman forward scattering (RFS). An increased high-energy electron yield has been observed for both methods. In addition, the influence of various laser and plasma parameters on the production of highly energetic electrons has been investigated. Specifically, the effects of plasma density ramps, skews in the temporal envelopes of the laser pulses, and laser frequency chirp (both pulse-length preserving and bandwidth preserving) have been examined. For each parameter, its influence on the yield of high-energy electrons can be explained from the way it affects the balance between RBS and RFS excitation in laser–plasma interaction.

Correlation effects play an important role in the description of turbulent transport. The present paper considers the influence of drift flow and time-dependence effects on the passive scalar behavior in the framework of the percolation approach. The renormalization method of a small parameter in continuum percolation models is reviewed. The modification is suggested of the renormalization condition of the small parameter of the percolation model in accordance with the additional external influences superimposed on the system. This approach makes it possible to consider simultaneously both parameters: the characteristic drift velocity $U_{\rm d}$ and the characteristic perturbation frequency $\omega $. The effective diffusion coefficient $D_{\rm eff} \,{\propto}\, \omega ^{1/7}$ satisfactorily describes the low-frequency region $\omega $, where the long-range correlation effects play a significant role. The character of the dependence of $D_{\rm eff}$ on the drift flow amplitude $U_{\rm d}$ in different regimes is analyzed.

The particle diffusion in a stochastic magnetic field is investigated by using the functional integral method. With the ensemble average of a functional representation to a kinetic equation over the fluctuating magnetic field and the random variables modeling the Coulomb collisions, a closed set of equations for an ensemble-averaged distribution function and a response function to an infinitesimal external perturbation is derived within the framework of the direct-interaction (DIA). By using the Markovian approximation to the equation for the response function, the cross-field diffusion coefficients are found to be obtained from nonlinear ordinary differential equations. Explicitly calculated diffusion coefficients for various parameters are also shown in the shearless and sheared configurations.

A dispersion relation is derived detailing the effect of a population of charged dust grains on the growth of lower-hybrid waves excited by a ring distribution of ions in a plasma. Numerical solutions show that the instability can be enhanced or reduced depending on the parameter regime.

We investigate the gravitational stability of partially ionized astrophysical plasmas, embedded in a large-scale magnetic field. The collisions between the charged particles and neutrals are incorporated into our model, and we study the influence of the ion–neutral collisions on the gravitational stability of a large space plasma, e.g. a large molecular cloud, and on the relevant growth/damping rates. The effects of the ion–neutral friction on the growth rate of a gravitationally unstable space plasma are presented for a range of possible wavenumbers.

We discuss here some of the physical problems related to the recently proposed scheme for solar sailing, using an artificial magnetosphere. We will concentrate on the forces acting on the plasma bubble, and their transfer to the spacecraft. Upper and lower limits of the force acting on the bubble are established. The results of test particle dynamics are presented, concerning the interaction of the solar wind with the modified magnetic dipole resulting from the spacecraft coils and the plasma expansion. Propagation of the forces along the magnetic flux tubes, from the bubble magnetopause down to the spacecraft vicinity, is discussed by using a simple MHD theoretical model. Emphasis is made on the distribution of currents flowing in the immediate vicinity of the spacecraft. Finally, results of PIC code simulations of the magnetized plasma expansion are presented and an overall qualitative picture of the physical processes is given, with a discussion of the strategy for obtaining more quantitative estimates of the magnetospheric propulsion efficiency.

This paper investigates the implications and consequences of choosing special gauges or gauge-invariant or non-gauge-invariant approximations in the action integral for the variational formulation of theories involving electromagnetic fields. After some interesting special gauges are considered, it is shown that non-gauge-invariant approximations always lead to inconsistent Euler–Lagrange equations. As a concrete example, Maxwell–Vlasov theory is investigated. The special non-gauge-invariant case considered, which is sometimes used in the literature, is obtained by replacing the contribution of the electric field to the Maxwell part of the Lagrangian density by the contribution of the gradient of the scalar potential alone. The detailed investigation concerns the local energy conservation law, and it is shown that the law thus derived is incorrect since it contains non-physical, spurious terms. An improvement of this situation can be obtained by the introduction of a Lagrange multiplier in the non-gauge-invariant theories in order to avoid inconsistencies in the local charge conservation law. The results are also valid for drift-kinetic and gyrokinetic theories, and for other theories, e.g. two-fluid theories.

The nonlinear wave propagation characteristics of ion acoustic (IA) solitary waves in a dusty plasma, i.e. dust ion acoustic (DIA) solitary waves in the presence of ionization, collisions of ions with dust grains and with the background neutral gas, have been investigated by employing a reductive perturbation technique. It has been found that the nonlinear DIA wave is governed by Korteweg–de Vries (KdV) equation with a positive or negative linear damping term. It has also been found that the ionization instability leads to the exponential growth of the DIA solitary wave amplitude with time, whereas ion–dust and ion–neutral collisions reduce the growth rate.

The nonlinear interaction, due to quantum electrodynamical effects, between photons is investigated using a wave-kinetic description. Starting from a coherent wave description, we use the Wigner transform technique to obtain a set of wave-kinetic equations, the so called Wigner–Moyal equations. These equations are coupled to a background radiation fluid, whose dynamics are determined by an acoustic wave equation. In the slowly varying acoustic limit, we analyse the resulting system of kinetic equations, and show that they describe instabilities, as well as Landau-like damping. The instabilities may lead to the break-up and focusing of ultra-high-intensity multi-beam systems, which in conjunction with the damping may result in stationary strong field structures. The results could be of relevance for the next generation of laser–plasma systems.