We present an investigation of the amplitude modulation of an external magnetic field-aligned right-hand circularly polarized electromagnetic electron-cyclotron (EMEC) wave in a strongly magnetized electron-positron plasma. It is shown that the dynamics of the modulated EMEC wave packet is governed by a cubic nonlinear Schrödinger equation. The latter reveals that a modulated wave packet can propagate in the form of either a dark or a grey envelope soliton. This result could have relevance to the transport of electromagnetic wave energy over long distances via envelope solitons in the magnetospheres of pulsars and magnetars.

Exact nonlinear (arbitrary amplitude) wave-like solutions of an incompressible, magnetized, non-dissipative two-fluid system are found. It is shown that, in 1-D propagation, these fully nonlinear solutions display a rare property; they can be linearly superposed.

The second line after Eq. (18) p. 71 should read

We estimate the total cross sections for field-stimulated photoemissions and photoabsorptions by quasi-free electrons within a non-equilibrium plasma evolving from the strong coupling to the weak coupling regime. Such a transition may occur within laser-created plasmas, when the initially created plasma is cold but the heating of the plasma by the laser field is efficient. In particular, such a transition may occur within plasmas created by intense vacuum ultraviolet (VUV) radiation from a free-electron laser (FEL) as indicated by the results of the first experiments performed by Wabnitz at the FLASH facility at DESY. In order to estimate the inverse bremsstrahlung cross sections, we use point-like and effective atomic potentials. For ions modelled as point-like charges, the total cross sections are strongly affected by the changing plasma environment. The maximal change of the cross sections may be of the order of 75 at the change of the plasma parameters: inverse Debye length, κ, in the range κ = 0 − 3 Å−1 and the electron density, ρe, in the range ρe = 0.01 − 1 Å−3. These ranges correspond to the physical conditions within the plasmas created during the first cluster experiments performed at the FLASH facility at DESY. In contrast, for the effective atomic potentials the total cross sections for photoemission and photoabsorption change only by a factor of seven at most in the same plasma parameter range. Our results show that the inverse bremsstrahlung cross section estimated with the effective atomic potentials is not affected much by the plasma environment. This observation validates the estimations of the enhanced heating effect obtained by Walters, Santra and Greene. This is important as this effect may be responsible for the high-energy absorption within clusters irradiated with VUV radiation.

It is shown that electrostatic ion-cyclotron (EIC)-like modes can be excited by the pre-existing electron density ripple across the external magnetic field in a dusty magnetoplasma. For this purpose, we use the ion continuity and momentum equations, together with the Boltzmann-distributed electrons, and derive the standard Mathieu equation. The latter admits unstable solutions, demonstrating that the EIC-like modes in dusty magnetoplasmas can be driven due to the free energy in the electron density ripple.

We define as the Rydberg plasma the weakly ionized gas produced in magneto-optical traps. In such a plasma, the neutral atoms can be excited in Rydberg states. Wave propagation in Rydberg plasmas and the mutual influence of plasma dispersion and atomic dispersion are considered. New dispersion relations are established, showing new instability regimes and new cut-off frequencies.

We investigate the dispersion property of a low-frequency electrostatic wave in a dense metallic electron-hole-ion plasma with nanoparticles. The latter are charged due to the field emission, and hence the metallic nanoparticles/nanotubes can be regarded as charged dust rods surrounded by degenerate electrons and holes, and non-degenerate ions. By using a quantum hydrodynamic model for the electrons and holes, we obtain the electron and hole number density perturbations, while the ion and dust rod number density perturbations follow the classical expressions. A dispersion relation for the low-frequency electrostatic wave in our multi-species dense metallic plasma is derived and analyzed. The possibility of exciting non-thermal electrostatic waves is also discussed.

Typically a magnetohydrodynamical model for neutral plasmas must take into account both the ionic and the electron fluids and their interaction. However, at short time scales, the ionic fluid appears to be stationary compared to the electron fluid. On these scales, we need consider only the electron motion and associated field dynamics, and a single fluid model called the electron magnetohydrodynamical model which treats the ionic fluid as a uniform neutralizing background applies. Using Maxwell's equations, the vorticity of the electron fluid and the magnetic field can be combined to give a generalized vorticity field, and one can show that Euler's equations govern its behavior. When the vorticity is concentrated into slender, periodic, and nearly parallel (but slightly three-dimensional) filaments, one can also show that Euler's equations simplify into a Hamiltonian system and treat the system in statistical equilibrium, where the filaments act as interacting particles. In this paper, we show that, under a mean-field approximation, as the number of filaments becomes infinite (with appropriate scaling to keep the vorticity constant) and given that angular momentum is conserved, the statistical length scale, R, of this system in the Gibbs canonical ensemble follows an explicit formula, which we derive. This formula shows how the most critical statistic of an electron plasma of this type, its size, varies with angular momentum, kinetic energy, and filament elasticity (a measure of the interior structure of each filament) and in particular it shows how three-dimensional effects cause significant increases in the system size from a perfectly parallel, two-dimensional, one-component Coulomb gas.

The poloidal eigenmode of the geodesic acoustic mode (GAM) is studied in the limit of high safety factor. In this limit, the poloidal gyroradius cannot be treated as a perturbation or as an expansion parameter. Analytical expressions for the poloidal structure of the GAM potential, the radial wavenumber dependence of the frequency, the phase velocity, and the group velocity are obtained. The spatial structure of the poloidal eigenmode including the higher-order gyroradius effect is revealed theoretically.

The equivalent photon charge in a two-electron temperature Fermi plasma is determined through the plasma physics method. The Fermi plasma has distinct populations of hot and cold electrons that are described by a quantum hydrodynamic model which accounts for the quantum statistical pressure of the hot electrons and the quantum force acting on the two electron fluids. Relations for the coupling between the electron plasma density fluctuations and the radiation fields are derived, and the effective photon charge is then calculated.

We investigate the drift dissipative instability in a non-uniform magnetized plasma composed of electrons, positive ions, negative ions and negatively charged dust particles. We use a multi-fluid plasma model and derive a dispersion relation for the electrostatic drift waves with frequencies much smaller than the ion gyrofrequencies and wavelengths longer than the ion gyroradii. The presence of the negatively charged, massive dust grains affects the drift wave frequency and the growth rate of the drift dissipative instability. The present results may be relevant to space and laboratory magnetoplasmas containing negative ions and charged dust grains.

The question of magnetic field structure in the vicinity of the separatrix in divertor tokamaks is studied. The authors have investigated this problem earlier in a series of papers, using various mathematical techniques. In the present paper, the two-wire model (TWM) [Reiman, A. 1996 Phys. Plasmas3, 906] is considered. It is noted that, in the TWM, it is useful to consider an extra equation expressing magnetic flux conservation. This equation does not add any more information to the TWM, since the equation is derived from the TWM. This equation is useful for controlling the step size in the numerical integration of the TWM equations. The TWM with the extra equation is called the flux-preserving TWM. Nevertheless, the technique is apparently still plagued by numerical inaccuracies when the perturbation level is low, resulting in an incorrect scaling of the stochastic layer width. The stochastic broadening of the separatrix in the flux-preserving TWM is compared with that in the low mn (poloidal mode number m and toroidal mode number n) map (LMN) [Ali, H., Punjabi, A., Boozer, A. and Evans, T. 2004 Phys. Plasmas11, 1908]. The flux-preserving TWM and LMN both give Boozer–Rechester 0.5 power scaling of the stochastic layer width with the amplitude of magnetic perturbation when the perturbation is sufficiently large [Boozer, A. and Rechester, A. 1978, Phys. Fluids21, 682]. The flux-preserving TWM gives a larger stochastic layer width when the perturbation is low, while the LMN gives correct scaling in the low perturbation region. Area-preserving maps such as the LMN respect the Hamiltonian structure of field line trajectories, and have the added advantage of computational efficiency. Also, for a degree of freedom Hamiltonian system such as field lines, maps do not give Arnold diffusion.

A Korteweg–de Vries (KdV) equation is derived here, that describes the nonlinear behaviour of long-wavelength weakly nonlinear dust acoustic waves propagating in an arbitrary direction in a plasma consisting of static negatively charged dust grains, non-thermal ions and isothermal electrons. It is found that the rarefactive or compressive nature of the dust acoustic solitary wave solution of the KdV equation does not depend on the dust temperature if σdc < 0 or σdc > σd*, where σdc is a function of β1, α and μ only, and σd*(<1) is the upper limit (upper bound) of σd. This β1 is the non-thermal parameter associated with the non-thermal velocity distribution of ions, α is the ratio of the average temperature of the non-thermal ions to that of the isothermal electrons, μ is the ratio of the unperturbed number density of isothermal electrons to that of the non-thermal ions, Zdσd is the ratio of the average temperature of the dust particles to that of the ions and Zd is the number of electrons residing on the dust grain surface. The KdV equation describes the rarefactive or the compressive dust acoustic solitary waves according to whether σdc < 0 or σdc > σd*. When 0 ≤ σdc ≤ σd*, the KdV equation describes the rarefactive or the compressive dust acoustic solitary waves according to whether σd > σdc or σd < σdc. If σd takes the value σdc with 0 ≤ σdc ≤ σd*, the coefficient of the nonlinear term of the KdV equation vanishes and, for this case, the nonlinear evolution equation of the dust acoustic waves is derived, which is a modified KdV (MKdV) equation. A theoretical investigation of the nature (rarefactive or compressive) of the dust acoustic solitary wave solutions of the evolution equations (KdV and MKdV) is presented with respect to the non-thermal parameter β1. For any given values of α and μ, it is found that the value of σdc completely defines the nature of the dust acoustic solitary waves except for a small portion of the entire range of the non-thermal parameter β1.

Electron and proton acceleration by a drifted super-Dreicer electric field is investigated in a strongly compressed non-neutral reconnecting current sheet (NRCS). The guiding field is assumed to be constant within a reconnecting current sheet (RCS) and parallel to the direction of the drifted electric field. The other two magnetic field components, transverse and tangential, are considered to vary exponentially and linearly with distances from the X-nullpoint. The proton and electron energy spectra are calculated numerically in a model RCS with different magnetic field topologies by solving an equation of motion in the test-particle approach with some test with a particle-in-cell (PIC) approach. Three kinds electric field generated inside a RCS are considered: a drifted electric field caused by the plasma inflows formed during a magnetic reconnection process; a polarization electric field induced by the accelerated protons and electrons; and a turbulent electric field induced by instabilities generated by accelerated particles. Electron and proton densities, and energy spectra inside a RCS and at ejection are found to be strongly affected by the magnetic field topology: for stronger magnetic fields the spectra are softer having a small higher-energy cutoff while for weaker magnetic fields the spectra are harder with much larger upper cutoff energies. Depending on the magnetic component ratios and drifted electric field magnitude, particles are found to be ejected either as quasi-thermal flows with very high temperatures or as focused power-law beams. A polarization field is found to reduce the acceleration time inside a RCS and to increase the energy gained by particles at acceleration by a pure drifted electric field by a few orders of magnitude. The turbulent electric field induced by the two beam instabilities of the same kind of particles leads to a significant increase in the number of particles with higher energies resulting in a flattening of their energy spectra.

Nonlinear resonant interaction between energetic particles and quasi-electrostatic wave propagating perpendicularly to the ambient magnetic field in a homogeneous plasma is studied in detail, with the main focus on the wave amplification or attenuation caused by resonant interaction. As for k∥ → 0, resonance velocity determined from linear resonance conditions tends to infinity, the interaction under discussion is a completely nonlinear phenomenon. While the wave amplitude may increase or decrease depending on the wave parameters and integral characteristics of the energetic particle distribution function, an essential wave amplification may occur when the wave frequency is close to a multiple of cyclotron harmonic, and when the transversal energy of resonant particles is large enough.

It is shown that when the non-isothermal trapped electron current is rederived based on the orbit-limited motion theory, the variable dust charge can be expressed in terms of the Lambert function. One can then take advantage of this new transcendental function to illustrate how variable-charge nonlinear trapped dust modes can be investigated semi-analytically.

This paper presents an analysis and subsequent discussion of the self focusing of a dark hollow Gaussian electromagnetic beam (HGB) in a magnetoplasma, considering ponderomotive and collisional nonlinearities. A paraxial-like approach, in which the relevant parameters are expanded in terms of radial distance from the maximum of the irradiance rather than that from the axis, has been adopted to analyze the propagation of the HGB. The nature of self focusing is highlighted through the critical curves as a plot of dimensionless radius versus power of the beam. The effect of the magnetic field and the nature of the nonlinearity on self focusing of various order HGBs has also been explored.

We reconsider the theory for three-wave interactions in cold plasmas. In particular, we demonstrate that previously overlooked formulations of the general theory are highly useful when deriving concrete expressions for specific cases. We also point out that many previous results deduced directly from the basic plasma equations contain inappropriate approximations leading to unphysical results. Finally, generalizations to more elaborate plasma models containing, for example, kinetic effects are given.

The Experimental Advanced Superconducting Tokamak (EAST) has a major radius of R0 = 1.75 m and a midplane halfwidth of 0.5 m. It has been operated with a toroidal magnetic field B0 = 2 T and Ip ≤ 500 kA. The evolution of the plasma equilibrium is analysed between discharges by Equilibrium Fitting Code (EFIT). Limiter, single-null and double-null diverted configurations have been produced. A plasma elongation in the range 1.3 ≤ κ ≤ 1.9 and a triangularity in the range 0.1 ≤ δ ≤ 0.55 have been sustained. The operation space of elongated discharges is also presented based on the EAST database.

The excitation of electrostatic ion wakefields by electromagnetic pulses in a very dense plasma is considered. For this purpose, a wave equation for the ion wakefield in the presence of the ponderomotive force of the electromagnetic waves is obtained. Choosing a typical profile for the electromagnetic pulse, the form of the ion wakefields is deduced. The electromagnetic wave-generated ion wakefields can trap protons and accelerate them to high energies in dense plasmas.