In this study, non-paraxial nonlinear propagation of a relativistic laser pulse with linear and circular polarization in a preformed plasma channel having a parabolic density profile is investigated. The circular laser spot size variation in the absence/presence of an external longitudinal magnetic field is separately analysed and the results are compared. The amplitude of oscillation is decreased in the relativistic case, but it is changed in the presence of an external field. The right-turn circular pulse behaviour is completely opposite to that of the left-turn circular pulse in the presence of an external field, because the right-turn pulse is focused later than the left-turn pulse. The effect of nonlinearities on oscillations of spot size is analysed and the nonlinear critical channel depth required for propagation of a self-trapped laser pulse is evaluated. The laser field amplitude is derived for a matched pulse and it is shown that the group velocity dispersion effect causes broadening of the pulse length.

Plasma instabilities play a important role in producing small-scale irregularities in the ionosphere. In particular, current-driven electrostatic ion-acoustic (CDEIA) instabilities contribute to high-latitude F-region electrodynamics. Ion temperature anisotropies with enhanced perpendicular temperature often exist in the high-latitude F-region. In addition to temperature anisotropies, ion velocity shears are observed near auroral arc edges, sometimes coexisting with thermal ion upflow processes and field-aligned currents (FAC). We investigated whether ion temperature anisotropy lowers the threshold conditions required for the onset of sheared CDEIA instabilities. We generalised a dispersion relation to include ion thermal anisotropy, finite Larmor radius corrections and collisions. We derived new fluid-like analytical expressions for the threshold conditions required for instability that depend explicitly on ion temperature anisotropy. We studied how the instability threshold conditions vary as a function of the wave vector direction in both fluid and kinetic regimes. We found that, despite the dampening effect of collisions on ion-acoustic waves, ion temperature anisotropy lowers in some cases the threshold drift requirements for a large range of oblique wave vector angles. More importantly, realistic ion temperature anisotropies contribute to reducing the instability threshold velocity shears that are associated with small drift thresholds, for modes propagating almost perpendicularly to the geomagnetic field. Small shear thresholds that seem to be sustainable in the ionospheric F-region are obtained for low-frequency waves. Such instabilities could play a role in the direct generation of field-aligned irregularities in the collisional F-region that could be observed with the Super Dual Auroral Radar Network (SuperDARN) array of high-frequency radars. These modes would be very sensitive to the radar probing direction since they are restricted to very narrow angular intervals. The ion temperature anisotropy is an important parameter that needs to be considered in the studies of sheared and collisional CDEIA waves and instabilities in the high-latitude F-region.

A recent paper by Webb et al. (J. Plasma Phys., vol. 80, 2014, pp. 707–743) on multi-symplectic magnetohydrodynamics (MHD) using Clebsch variables in an Eulerian action principle with constraints is further extended. We relate a class of symplecticity conservation laws to a vorticity conservation law, and provide a corrected form of the Cartan–Poincaré differential form formulation of the system. We also correct some typographical errors (omissions) in Webb et al. (J. Plasma Phys., vol. 80, 2014, pp. 707–743). We show that the vorticity–symplecticity conservation law, that arises as a compatibility condition on the system, expressed in terms of the Clebsch variables is equivalent to taking the curl of the conservation form of the MHD momentum equation. We use the Cartan–Poincaré form to obtain a class of differential forms that represent the system using Cartan’s geometric theory of partial differential equations

We investigate the low-frequency (by comparison with the ion Larmor frequency) electrostatic solitary structures in a spatially non-uniform electron–positron–ion (e–p–i) magnetoplasma with non-Maxwellian electrons. A linear dispersion relation for the obliquely propagating ion acoustic drift wave is derived and it is shown that the non-Maxwellian electron population modifies the dispersion characteristics of the wave under consideration. We also carry out a nonlinear analysis and derive the modified Zakharov–Kuznetsov (MZK) equation for the coupled drift acoustic wave in a non-uniform magnetized plasma. We highlight the differences between the MZK equation and its homogeneous counterpart. We also find the solution of the MZK equation using the tangent hyperbolic method. It is observed that the electron spectral index ${\it\kappa}$, positron concentration, and propagation angle ${\it\alpha}$ alter the structure of the ion acoustic drift solitary waves. The results obtained in this paper may be beneficial to understanding the propagation characteristics of electrostatic drift solitary structures in the interstellar medium and in laboratory experiments where electron–positron plasmas have recently been created by impinging ultra-intense laser pulses on a solid density target at the Lawrence Livermore National Laboratory (LLNL).

We consider fast sausage waves in straight homogeneous magnetic tubes. The plasma motion is described by the ideal magnetohydrodynamic equations in the cold plasma approximation. We derive the nonlinear Schrödinger equation describing the nonlinear evolution of an envelope of a carrier wave. The coefficients of this equation are expressed in terms Bessel and modified Bessel functions. They are calculated numerically for various values of parameters. In particular, we show that the criterion for the onset of the modulational or Benjamin–Fair instability is satisfied. The implication of the obtained results for solar physics is discussed.

In this paper, we study the (3+1)-dimensional generalized Johnson model, which can be used to describe the dust-ion-acoustic waves in a cosmic unmagnetized dusty plasma, and its perturbed model, which can be found in an unmagnetized dusty plasma for the electron temperature below the Curie temperature. (I) For the original model: Bilinear form and soliton solutions are obtained. Amplitude of the one soliton reaches the maximum when the equilibrium electron (ne0) and ion (ni0) densities take certain values which correspond with ne0/ni0 = 2. Overtaking and head-on interactions between the two solitons are given. (II) For the perturbed model: Phase projections are given numerically. Via the spectral analysis, two kinds of chaotic motions, i.e., the weak and developed chaos, are investigated. Largest Lyapunov exponents and power spectra are investigated to corroborate that those motions are indeed chaotic. Dynamic behavior of such a perturbed model varying with the external perturbation is different when the nonlinear term changes. With the damped term considered, two kinds of periodic motions are studied, and spectra of those periodic motions are also given. Through the comparison between the chaotic motions and periodic ones, possible chaotic or periodic motions in the perturbed model can be predicted.

Since the electromagnetic energy gained by the laser wave in a free-electron laser (FEL) is transferred from the kinetic energy loss of a relativistic electron beam, the stability of electron motion is one of the key factors that affect FEL performance. In this paper the stability of electron motion is compared for different focusing regimes. It is demonstrated that the natural focusing regime of a three-dimensional wiggler is easily broken by the self-field of the electron beam. The magnetic focusing regime of an axial guide magnetic field is based on the superposition of a strong Larmor rotation on the transverse quiver motion of the electrons, while the electric focusing regime of an ion-channel guiding field generates an electric force to counteract the divergent effect of the beam self-field. In comparison with the magnetic focusing regime of an external magnetic system, the electric focusing regime of an ion-channel guiding field may yield smaller instantaneous Larmor radius and slighter Larmor-centre deviation from the axis and provide better motion stability.

Large amplitude ion-acoustic double layer (IADL) is studied using Sagdeev's pseudo-potential technique in collisionless unmagnetized plasma comprising hot and cold Maxwellian population of electrons, warm adiabatic ions, and dust grains. Variation of both Mach number (M) and amplitude |φm| of large amplitude IADL with charge, concentration, and mass of heavily charged massive dust grains is investigated for both positive and negative dust in plasma. Our numerical analysis shows that system supports only rarefactive large amplitude IADL for the selected set of plasma parameters. Our investigations for both negative and positive dust grains reveal that ion temperature increases the mobility of ions, resulting in increase in the Mach number of IADL. The larger mobility of ions causes leakage of ions from localized region, resulting into decrease in the amplitude of IADL. Other parameters, e.g. temperature ratio of hot to cold electrons, charge, concentration, mass of heavily charged massive dust grains also play significant role in the properties and existence of double layers. Since it is well established that both positive and negative dust are found in space as well as laboratory plasma, and double layers have a tremendous role to play in astrophysics, we have included both positive and negative dust in our numerical analysis for the study of large amplitude IADL. Further data used for negative dust are close to experimentally observed data. Hence, it is anticipated that our parametric studies for heavily charged (both positive and negative) dust may be useful in understanding laboratory plasma experiments, identifying nonlinear structures in upper part of ionosphere and lower part of magnetosphere structures, and in theoretical research for the study of properties of nonlinear structures.

The effect of a guide field on the saturation mechanism in a two-stream free-electron laser (FEL) is verified. Two monoenergetic electron beams with a vanishing pitch-angle spread are considered. Nonlinear wave–particle interaction is described by a set of coupled differential equations in a 1-D approximation. Output power is presented as a function of the axial distance. It was found that through using a focusing mechanism, the two-stream FEL reached the saturation regime in a shorter axial distance in comparison with the case of no focusing mechanism.

By solving the coupled equations of the electromagnetic field and electrostatic potential, we investigate solitary waves in an asymmetric electron–positron plasma and/or electron–positron–ion plasmas with delicate features. It is found that the solutions of the coupled equations can capture multipeak structures of solitary waves in the case of cold plasma, which are left out by using the long-wavelength approximation. By considering the effect of ion motion with respect to non-relativistic and ultra-relativistic temperature plasmas, we find that the ions’ mobility can lead to larger-amplitude solitary waves; especially, this becomes more obvious for a high-temperature plasma. The effects of asymmetric temperature between electrons and positrons and the ion fraction on the solitary waves are also studied and presented. It is shown that the amplitudes of solitary waves decrease with positron temperature in asymmetric temperature electron–positron plasmas and decrease also with ion concentration.

A version of Noether's second theorem using Lagrange multipliers is used to investigate fluid relabelling symmetries conservation laws in magnetohydrodynamics (MHD). We obtain a new generalized potential vorticity type conservation equation for MHD which takes into account entropy gradients and the J × B force on the plasma due to the current J and magnetic induction B. This new conservation law for MHD is derived by using Noether's second theorem in conjunction with a class of fluid relabelling symmetries in which the symmetry generator for the Lagrange label transformations is non-parallel to the magnetic field induction in Lagrange label space. This is associated with an Abelian Lie pseudo algebra and a foliated phase space in Lagrange label space. It contains as a special case Ertel's theorem in ideal fluid mechanics. An independent derivation shows that the new conservation law is also valid for more general physical situations.

Dust acoustic solitary waves, blow-up solitary waves and periodic waves have been investigated in unmagnetized dusty plasmas with Maxwell-distributed electrons and ions, considering dust charge fluctuations using the bifurcation theory of planar dynamical systems. The basic equations are transformed to an ordinary differential equation involving the electrostatic potential. Applying the bifurcation theory of planar dynamical systems, we have established the existence of solitary, blow-up solitary and periodic waves. Four exact solutions of the solitary, blow-up solitary and periodic waves are derived depending on the physical parameters. Regarding the solitary, blow-up solitary and periodic waves, we have presented the combined effects of the density ratio of electrons and ions (${\it\alpha}$), the temperature ratio of electrons and ions $({\it\beta})$ and the speed of the travelling wave ($v$) on the characteristics of dust acoustic solitary, blow-up solitary and periodic waves.

In previous works, we derived stationary density distribution functions (DDF) where the local equilibrium is determined by imposing the maximum entropy (MaxEnt) principle, under the scale invariance restrictions, and the minimum entropy production theorem. In this paper we demonstrate that it is possible to reobtain these DDF solely from the MaxEnt principle subject to suitable scale invariant restrictions in all the variables. For the sake of concreteness, we analyse the example of ohmic, fully ionized, tokamak-plasmas, in the weak-collisional transport regime. In this case we show that it is possible to reinterpret the stationary distribution function in terms of the Prigogine distribution function where the logarithm of the DDF is directly linked to the entropy production of the plasma. This leads to the suggestive idea that also the stationary neoclassical distribution functions, for magnetically confined plasmas in the collisional transport regimes, may be derived solely by the MaxEnt principle.

The nonlinear properties of the ion acoustic waves (IAWs) in a three-component quantum plasma comprising electrons, and positive and negative ions are investigated analytically and numerically by employing the quantum hydrodynamic (QHD) model. The Sagdeev pseudopotential technique is applied to obtain the small-amplitude soliton solution. The effects of the quantum parameter $H$, positive to negative ion density ratio ${\it\beta}$ and Mach number on the nonlinear structures are investigated. It is found that these factors can significantly modify the properties of the IAWs. The existence of quasi-periodic and chaotic oscillations in the system is established. Switching from quasi-periodic to chaotic is possible with the variation of Mach number or quantum parameter $H$.

A misprint occured in equation 26 in the original article (Ur-Rahman et al. 2013). The correct equation is provided below.

\[ \zeta=\epsilon^{1/2}\left(x-\lambda t\right) \rm{, \ \ }\tau=\epsilon^{3/2}t\rm{.}% \]

Based on large-signal theory, a one-dimensional theoretical model of a coaxial vircator is developed to give the microwave gain of the nonlinear beam–wave interaction, and the effect of injected current premodulation on the microwave gain is analysed theoretically. In addition, a coaxial vircator with improved dual-cavity modulation structure, which has the advantage of enhancing the effect of the modulation cavity on the injected electron beam by way of feedback microwaves, is presented. The simulation results are presented to test the validity of the proposed theory, and it can be seen that the system power efficiency can become further strengthened by adjusting the parameters of the microwave feedback channel until the feedback electric field is at the proper phase. Finally, through optimization, a structure capable of generating 7.05 GW average output power and 19.5 % power conversion efficiency at 2.95 GHz operating frequency is obtained.

We review the generation of zonal flow and magnetic field by coupled electromagnetic ultra-low-frequency waves in the Earth’s ionospheric E-layer. It is shown that, under typical ionospheric E-layer conditions, different planetary low-frequency waves can couple with each other. Propagation of coupled internal-gravity–Alfvén, coupled Rossby–Khantadze and coupled Rossby–Alfvén–Khantadze waves is revealed and studied. A set of appropriate equations describing the nonlinear interaction of such waves with sheared zonal flow is derived. The conclusion on the instability of short-wavelength turbulence of such coupled waves with respect to the excitation of low-frequency and large-scale perturbation of the sheared zonal flow and sheared magnetic field is deduced. The nonlinear mechanism of the instability is based on the parametric triple interaction of finite-amplitude coupled waves leading to the inverse energy cascade towards longer wavelength. The possibility of generation of an intense mean magnetic field is shown. Obtained growth rates are discussed for each case of the considered coupled waves.

Many naturally occurring and man-made plasmas are collisionless and turbulent. It is not yet well understood how the energy in fields and fluid motions is transferred into the thermal degrees of freedom of constituent particles in such systems. The debate at present primarily concerns proton heating. Multiple possible heating mechanisms have been proposed over the past few decades, including cyclotron damping, Landau damping, heating at intermittent structures and stochastic heating. Recently, a community-driven effort was proposed (Parashar & Salem, 2013, arXiv:1303.0204) to bring the community together and understand the relative contributions of these processes under given conditions. In this paper, we propose the first step of this challenge: a set of problems and diagnostics for benchmarking and comparing different types of 2.5D simulations. These comparisons will provide insights into the strengths and limitations of different types of numerical simulations and will help guide subsequent stages of the challenge.

An axially symmetric laser beam configuration irradiating a spherical capsule has been considered in the context of inertial confinement fusion (ICF). The laser beams are located at co-latitudes 49° and 131° and mimic the quad positions in the second cone of the Laser Mégajoule Facility. The capsule is directly irradiated by the laser beams whose energy deposition generates a nearly spherical shock wave. Two-dimensional hydrodynamic numerical simulations have been performed to analyse the non-uniformity of the shock wavefront launched inward throughout the target. Different laser intensity profiles, calculated by the illumination model, have been tested. The performance, in terms of shock non-uniformity, has been compared, and it is found that with an appropriate choice of the laser intensity profile it is possible to control the shock non-uniformity at early times.