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 relation (DR) has been considered for low-frequency waves in a hot magnetoactive collisional plasma with ‘longitudinal’ large-scale electric field ${\bf E}_{0} ( {t} )$ and weak spatial inhomogeneity of temperature. The electric field was assumed to be extremely weak (‘subdriecer’ field) and the quasi-static time variation of its amplitude allows us to use the ‘direct initiation’ mechanism to describe the instability development. Taking into account the ion thermal motion has not changed the form of the DR, which has remained the polynomial of the fourth order, but it has essentially complicated the form of its coefficients. As compared with previous investigations, these changes have resulted in the changes of the solutions of the DR. Two of the roots of the DR have remained of the same type (‘kinetic Alfvén-like’ waves), but another two have become quite different and get to the range of slow magneto-acoustic waves. Investigation of these new waves has shown that corresponding instability has clearly expressed threshold character, and the value of this threshold depends essentially on the reduced value of the electric field amplitude $E_{0} (t)$ and ratio of electron and ion temperatures.

The mechanism of gyroresonant scattering of charged particles by small-amplitude, broadband electromagnetic waves is examined. By means of quasi-linear theory, a simple expression for the resonant pitch-angle diffusion coefficient $D_{\alpha \alpha}$ is developed, which is valid for parallel-propagating, small-amplitude, (R-mode or L-mode) electromagnetic waves of general spectral density. We calculate the average diffusion coefficient with respect to the pitch-angle $\alpha$, namely $\langle D_{\alpha\alpha}\rangle$, which provides a practical estimate for particle scattering rates as a function of particle kinetic energy. The results for $\langle D_{\alpha\alpha}\rangle$, corresponding to a Gaussian wave frequency spectrum, are used to estimate scattering rates for several types of wave–particle interactions in the terrestrial and Jovian magnetospheres.

A study of the two-dimensional incompressible flow of the solar wind past an open terrestrial magnetosphere is presented. The plasma is described by the magnetohydrodynamic (MHD) equations including non-ideal effects such as resistivity and viscosity. The theoretical analysis is based on an ordinary perturbation technique with expansion in orders of large Reynolds and Lundqvist numbers. Magnetic reconnection is assumed to occur at an arbitrary point along a region of the magnetopause, stretching from the sub-solar point to the north. From the analysis we find analytical solutions describing the transition layers north and south of a reconnection point. It is shown that the transition layer north of the reconnection point is thinner than the layer on the south side. It is also shown that in order for steady reconnection to occur, the velocity at the reconnection point must be less than the Alfvén velocity. Using the method of matched asymptotic expansions, we match the transition layer solution with a potential flow solution describing the flow and magnetic field in the exterior magnetosheath.

A brief history of the concept of negative energy waves in fluid and plasma media is given. The theory of microwave tubes is highlighted, where the small signal power theorem was first derived, which led to the interpretation of these devices in terms of the interaction of positive and negative energy waves. Three examples are described to illustrate the use of negative waves in stability problems. The first is concerned with the Kelvin–Helmholtz instability in neutral fluids. The second comes from a kinetic theory of instability in a collisionless shock wave in a magnetized plasma, and the third is concerned with the effect of a resistive wall and plasma flow on the magnetohydrodynamic stability of a magnetically confined plasma. The paper ends with some general conclusions.

Using a new technique following the Bogoliubov Mitropolsky method, higher-order nonlinear and dispersive effects are obtained for a kinetic Alfvén wave and ion-acoustic wave with two temperature isothermal electrons, starting from a set of equations that lead to a linear dispersion relation coupling kinetic Alfvén wave ion-acoustic wave. Higher-order solitary wave profiles are obtained for both waves. Graphs are plotted showing the variation of both the Mach number and soliton width against the soliton amplitude for different angles of propagation with the applied magnetic field. Amplitude, width and velocity are found to be greater for larger angles of propagation for both waves. It is found that the higher-order ion-acoustic wave moves faster than the Korteweg–de Vries (KdV) wave, but the higher-order Alfvén wave is slower. The higher-order amplitude and width of both waves are found to be less than those of KdV waves. The potential structure and widths of the double layer for both waves are shown graphically. It is found that the amplitude of the double layer is independent of the angles of propagation, but the widths are greater for larger angles of propagation for both waves.

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.

Poisson brackets in the phase space of averaging Kruskal coordinates are obtained in a clear and straightforward way. The derivation makes use of the equations of motion of guiding centres and gyrocentres derived from a gyroangle-independent Lagrangian, and from generally valid relations of Hamiltonian mechanics. The usual procedure of matrix inversion to obtain the Poisson tensor from the Lagrange tensor is not required.

A one-dimensional model of the interaction between an injected electron beam and an electromagnetic (EM) field inside a coaxial vircator is presented. The effects of the injected electron beam energy spread, anode absorption rate, feedback and injected current premodulation are analyzed. The EM-gains of interaction between the electron beam and TM01, TE11 modes are derived and discussed.

We present the Rayleigh instability of low-frequency (in comparison with the ion-gyrofrequency) electrostatic waves in multi-ion species plasmas containing equilibrium density gradient and transverse ion-sheared flows caused by the dc electric field. For this purpose, multi-fluid equations are used to obtain the governing equations for two-dimensional convective cells and pseudo-three-dimensional drift waves in a non-uniform magnetoplasma. Standard procedures are then employed to study the Raleigh instability. Thresholds and growth rates are obtained. Applications to Hall thrusters are discussed.

In this paper we analyze the transition from coherent to incoherent wave dynamics in a broad-band triplet interaction, where, in contrast to previous models, wave vector selection rules are imposed on the nonlinear terms of the governing equations. As a general rule, nonlinear terms induce coherence via a phase-locking process. However, wave vector spread also results from nonlinearity and can affect coherence when resonant modes are excited.

The reactive instabilities are characterized by the absence of dissipation, algebraic dispersion relations (in slab approximation) and the existence of marginal (bifurcation) points of stability. In the vicinity of these points the reactive instabilities are amenable to a thermodynamic treatment based on the electrostatic entropy concept. After recalling the essential aspects of this concept and its connection with the linear description of the electrostatic instabilities, the theory is extended to the nonlinear domain near the marginal point. It is shownthat the marginal state is a maximum of the electrostatic entropy with respect to arbitrary variations of the bifurcation parameter (e.g. the temperature gradient). However, a nonlinear neighboring electrostatic structure is formed, which is the manifestation, on average, of large-amplitude fluctuations towards the linearly unstable side of the marginal point. A correspondence with numerical models of turbulence involving ion temperature gradient (ITG) saturation is noted. Compact analytical expressions for the mean square amplitude of the fluctuations valid in the range from the stable to the unstable side of the marginal point are presented. As an example, the theory is applied in detail to the flute modes.

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 dynamics of thermally-isolated Z-pinches carrying power law in time total currents (${\sim} t^S$) in magnetized resistive plasmas is studied. Time–space separable self-similar solutions with cylindrical symmetry are considered. The non-dimensional variables are chosen in a way that makes the problem consistent with the moderately resistive magnetohydrodynamic (MHD) model. For $S\,{=}\,{-}\frac15$ and Lundquist number $Lu\,{>}\, 1.5$ a non-equilibrium solution is obtained in addition to the conventional solutions for either exact, $S\,{=}\,{\pm}\frac13$, or asymptotic, $Lu\,{=}\,\infty$, equilibria (the latter is homogeneously valid for long times only if $S\,{>}\,{-}\frac15$). The problem is treated asymptotically for high dimensionless thermal-conductivity, which is proportional to the square root of the ion/electron mass ratio. To obtain a closure condition for the leading-order isothermal solution, the first-order terms in the energy equation are invoked. Radial profiles are found explicitly which depend on $S$ for equilibrium, and on $Lu$ for non-equilibrium solutions. The multiplicity of the self-similar solutions is investigated.

A previous paper, McKenzie and Hagfors (1996 J. Plasma Phys. 55(3), 539–585) henceforth referred to as P1, discussed the excitation of parametric instability in a homogeneous plasma pumped by an external electrostatic field. The discussion was carried out in the fluid approximation, and growth rates and resonance frequencies for several different modes were calculated, some of which had previously been overlooked because of inconsistent cut-off of certain series expansions. In this brief note we show that the fluid treatment gives growth rates and resonance frequencies that agree well with the kinetic treatment.

Several high velocity clouds (HVCs) are now known to be soft X-ray sources. In this paper we suggest that an interaction between the HVCs and the galactic halo is leading to plasma instabilities that generate energetic electrons which in turn generate X-ray emission. This process is essentially analogous to the interaction process between comets and non-magnetized planets with the solar wind which is also known to lead to the generation of X-rays. We show that for reasonable assumptions about the galactic halo magnetic field, the X-ray emission can be converted into an estimate of the mean galactic halo density at the position of the cloud. This provides a method for estimating the baryonic mass of the plasma halo provided that we can obtain a good estimate for the distance to the HVC.

Using particle-in-cell computer simulation, the processes occurring in a plasma formed by isothermal evaporation of ions and electrons off a planar wall are studied. A simple model to implement three-body recombination is introduced into this scheme; it fulfills momentum and energy conservation and obeys the well-known dependences of the recombination rate on density and temperature. Ion acceleration processes are investigated, during both the particle emission phase and afterwards, during expansion into vacuum. Recombination strongly enhances ion acceleration, since due to the recombination-heated electron subsystem the expansion-front space-charge field is increased. Spatial segregation of the neutral gas cloud and the plasma cloud is demonstrated.

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.