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A "stiff transport" critical gradient model of energetic particle (EP) transport by EP-driven Alfvén eigenmodes (AEs) is verified against local nonlinear gyrokinetic simulations of a well-studied beam-heated DIII-D discharge 146102. A greatly simplifying linear "recipe" for the limiting EPdensity gradient (critical gradient) is considered here. In this recipe, the critical gradient occurs when the local AE linear growth rate, driven mainly by the EP gradient, exceeds the ion temperature gradient (ITG) or the trapped electron mode (TEM) growth rate, driven by the thermal plasma gradient, at the same toroidal mode number (n) as the AE peak growth, well below the ITG/TEM peak n. This linear recipe for the critical gradient is validated against the critical gradient determined from far more expensive local nonlinear simulations in the gyrokinetic code GYRO, as identified by the point of transport runaway when all driving gradients are held fixed. The reduced linear model is extended to include the stabilization from local equilibrium E×B velocity shear. The nonlinear verification unambiguously endorses one of two alternative recipes proposed in the study by Waltz et al. [Nucl. Fusion 55, 123012 (2015)]: the EP-driven AE growth rate should be determined with rather than without an added thermal plasma drive. [ABSTRACT FROM AUTHOR]

A nonlinear model and simulations of the output power of an ion-channel guiding free-electron laser (FEL) are presented in this paper. Results show that the nonlinear output power of an ionchannel guiding FEL is comparable to that of an axial guide magnetic field FEL. Compared to an axial guide magnetic field FEL, an ion-channel guiding FEL substantially weakens the negative effect of the electron-beam energy spread on the output power due to its advantageous focusing mechanism on the electron motion. [ABSTRACT FROM AUTHOR]

An investigation on the characteristics of self organized criticality (Soc) in ITG mode driven turbulence is made, with the use of various statistical tools (histograms, power spectra, Hurst exponents estimated with the rescaled range analysis, and the structure function method). For this purpose, local non-linear gyrokinetic simulations of the cyclone base case scenario are performed with the GENE software package. Although most authors concentrate on global simulations, which seem to be a better choice for such an investigation, we use local simulations in an attempt to study the locally underlying mechanisms of Soc. We also study the structural properties of radially extended structures, with several tools (fractal dimension estimate, cluster analysis, and two dimensional autocorrelation function), in order to explore whether they can be characterized as avalanches. We find that, for large enough driving temperature gradients, the local simulations exhibit most of the features of Soc, with the exception of the probability distribution of observables, which show a tail, yet they are not of power-law form. The radial structures have the same radial extent at all temperature gradients examined; radial motion (transport) though appears only at large temperature gradients, in which case the radial structures can be interpreted as avalanches. [ABSTRACT FROM AUTHOR]

The properties of nonlinear fast magnetoacoustic waves in dense dissipative plasmas with degenerate electrons are studied theoretically in the framework of the Zabolotskaya-Khokhlov (ZK) equation for small but finite amplitude excitations. Shock-like solutions of the ZK equation are obtained and are applied to parameters relevant to white dwarf stars. [ABSTRACT FROM AUTHOR]

We have presented the numerical simulation of the coupled equations governing the dynamics of kinetic Alfvén wave (KAW) and ion acoustic wave in the intermediateβ plasma, where β is the ratio of thermal pressure to the background magnetic pressure. We have also developed a simplified model for this nonlinear interaction using the results obtained from the simulation to understand the physics of nonlinear evolution of KAW. Localization of magnetic field intensity of KAW has been studied by means of the simplified model. [ABSTRACT FROM AUTHOR]

Structure formation and self-organization in two-dimensional drift-wave turbulence show up in many different faces. Fluctuation data from a magnetized plasma are analyzed and three mechanisms transferring kinetic energy to large-scale structures are identified. Beside the common vortex merger, clustering of vortices constituting a large-scale strain field and vortex thinning, where due to the interactions of vortices of different scales larger vortices are amplified by the smaller ones, are observed. The vortex thinning mechanism appears to be the most efficient one to generate large scale structures in drift-wave turbulence. Vortex merging as well as vortex clustering are accompanied by strong energy transfer to small-scale noncoherent fluctuations (dissipation) balancing the negative entropy generation due to the self-organization process. [ABSTRACT FROM AUTHOR]

Stationary solutions of Vlasov-Maxwell equations are obtained by exploiting the invariants of single particle motion and lead to linear or nonlinear functional relations between current and vector potential. The nonlinear relations support various special types of magnetic configurations including multiple current sheets and magnetic field discontinuities leading to singular current layers. It is demonstrated through the examples that in one dimension, the description of the equilibrium magnetic fields obeys double or higher-curl Beltrami equation. For the linear case, such representation gives the advantage of obtaining exact analytic solutions that are expressed as a superposition of the single-curl Beltrami fields. [ABSTRACT FROM AUTHOR]

The material of limiter in HT-7 tokamak was changed from graphite to molybdenum in the last experimental campaign. The pitch angle scattering of runaway electrons due to anomalous Doppler resonance effects was observed. The experimental results agree very well with the stable boundary condition expected from the linear resistive theory but only agree with that from the nonlinear evolutionary of runaway-electron distribution theory in low electric field region. The current carried by runaway electrons is the same under different limiter conditions. [ABSTRACT FROM AUTHOR]

In the present paper, the transport of impurities driven by trapped electron (TE) mode turbulence is studied. Non-linear (NL) gyrokinetic simulations using the code GENE are compared with results from quasilinear (QL) gyrokinetic simulations and a computationally efficient fluid model. The main focus is on model comparisons for electron temperature gradient driven turbulence regarding the sign of the convective impurity velocity (pinch) and the impurity density gradient R/LnZ (peaking factor) for zero impurity flux. In particular, the scaling of the impurity peaking factors with impurity charge Z and with driving temperature gradient is investigated and compared with results for the more studied ion temperature gradient (ITG) driven turbulence. The question of helium ash removal in TE mode turbulence is also investigated. In addition, the impurity peaking is compared to the main ion peaking obtained by a self-consistent fluid calculation of the density gradients corresponding to zero particle fluxes. For the scaling of the peaking factor with impurity charge Z, a weak dependence is obtained from NL GENE and fluid simulations. The QL GENE results show a stronger dependence for low Z impurities and overestimates the peaking factor by up to a factor of two in this region. As in the case of ITG dominated turbulence, the peaking factors saturate as Z increases, at a level much below neoclassical predictions. The scaling with Z is, however, weak or reversed as compared to the ITG case. The results indicate that TE mode turbulence is as efficient as ITG turbulence at removing He ash, with DHe/χeff>1.0. The scaling of impurity peaking with the background temperature gradients is found to be weak in the NL GENE and fluid simulations. The QL results are also here found to significantly overestimate the peaking factor for low Z values. For the parameters considered, the background density gradient for zero particle flux is found to be slightly larger than the corresponding impurity zero flux gradient. [ABSTRACT FROM AUTHOR]

A rigorous theoretical investigation has been made on the formation of the nonlinear structures (viz., solitary waves, double layers) in a dusty electron-positron-ion plasma (containing inertialess degenerate electrons and positrons, cold, mobile, inertial ions, and negatively charged stationary dust). The pseudo potential method has been employed in this theoretical investigation. The basic features of the solitary waves and double layers, which are associated with positive ion dynamics and pressures of degenerate electrons and positrons, are identified. The co-existence of positive and negative solitary waves, and existence of either positive or negative double layers have been theoretically observed for certain range of different plasma parameters. The implications of our results in astrophysical compact objects have been briefly discussed. [ABSTRACT FROM AUTHOR]

We consider the weak turbulence of whistler waves in the in low-β inner magnetosphere of the earth. Whistler waves, originating in the ionosphere, propagate radially outward and can trigger nonlinear induced scattering by thermal electrons provided the wave energy density is large enough. Nonlinear scattering can substantially change the direction of the wave vector of whistler waves and hence the direction of energy flux with only a small change in the frequency. A portion of whistler waves return to the ionosphere with a smaller perpendicular wave vector resulting in diminished linear damping and enhanced ability to pitch-angle scatter trapped electrons. In addition, a portion of the scattered wave packets can be reflected near the ionosphere back into the magnetosphere. Through multiple nonlinear scatterings and ionospheric reflections a long-lived wave cavity containing turbulent whistler waves can be formed with the appropriate properties to efficiently pitch-angle scatter trapped electrons. The primary consequence on the earth's radiation belts is to reduce the lifetime of the trapped electron population. [ABSTRACT FROM AUTHOR]

A circuitry model is established to study the nonlinear dynamics of magnetron through solving a third order differential equation. The steady, oscillatory oscillation and even chaotic state have been observed when changing different control parameters, i.e., the anode current and the load. The observation of the anode current increase causing the magnetron to operate in chaos agrees well to that in the experiments conducted by other researchers. [ABSTRACT FROM AUTHOR]

In outer space physics and astrophysics, there is a considerable amount of anomalous phenomena that support nonextensive particle distribution. This is because of the relevance of gravitational forces (which are long ranged) as well as to a variety of dynamical nonlinear aspects. Here, we investigate the nonlinear properties and the existence conditions of a plasma system consisting of ion fluid as well as electrons and positrons modelled by nonextensive distributions. The numerical analysis of the evolution equation shows that both subsonic and supersonic electrostatic waves may exist. These nonlinear waves admit positive and negative localized structures. The dependence of the latter on the plasma parameters is investigated numerically. [ABSTRACT FROM AUTHOR]

The propagation of linear and nonlinear transverse off-plane dust lattice waves in 2D hexagonal dusty plasma crystals including the paramagnetic effects (magnetized particles) is investigated theoretically. The linear dispersion characteristics of transverse dust lattice waves are studied, including the dispersion relations, group velocities, and an evolution equation for the modulated amplitude of the first harmonic. The dispersion relations show a negative group velocity of the wave for a weak paramagnetic effect and a positive group velocity for a strong paramagnetic effect. The modulated wave packet is described by a nonlinear Schrodinger equation. The modulational stability of carrier wave depends on the form of the electric field, the magnetic field, and the magnetic permeability of dust particles. We found that the wave is modulationally unstable for long wavelength limit and weak (or zero) paramagnetic effects. [ABSTRACT FROM AUTHOR]

Nonlinear interplay between resistive magnetohydrodynamic (MHD) magnetic island and drift wave micro-turbulence is investigated using direct Landau-fluid simulations. A twisting oscillation of magnetic island associated with the driving force of micro-turbulence is observed, which is referred to as magnetic island seesaw. In the initiating phase of the seesaw oscillation, small-scale current and magnetic field fluctuations increase dramatically while the magnetic induction grows exponentially at small-scales corresponding to the spatial scale of micro-turbulence, showing a small-scale dynamo action. A minimal model consisting of reduced MHD turbulence and a micro-instability is proposed to elucidate the underlying mechanism. It is identified that the island seesaw is driven by a net oscillatory electromagnetic torque, which results from small-scale dynamo-generated current and magnetic field. The dynamo mechanism may offer an important energy exchange channel between MHD and micro-turbulence in magnetic fusion plasmas. [ABSTRACT FROM AUTHOR]

Resistive MHD computations using the NIMROD code have found strong dependence of the low-n edge localized instabilities on edge current density distribution. The computations confirm that the low-n edge localized modes can be driven unstable by increasing the edge current density. When the edge peaked current density is sufficiently large, the q profile develops a region where the magnetic shear becomes negative. In these cases, the low-n edge instabilities are partially or fully stabilized. The stabilizing effects of edge current density in regions with reversed magnetic shear appear to be consistent with analytical predictions on a necessary condition for the stability of peeling modes. Nonlinear simulations indicate that the stabilizing effects of edge current density on the low-n edge instabilities through reverse shear can persist throughout the nonlinear exponential growth phase. Near the end of this nonlinear phase, the filament size in radial direction can exceed the pedestal width, and disconnected blob-like substructures start to develop within the filaments. Relative pedestal energy loss from these radially extending filaments can reach above the average experimental level of 10%. [ABSTRACT FROM AUTHOR]

Experiments on accelerating NBI-produced deuterium (D) beam ions from their injection energy of ∼110 keV up to the MeV energy range with 3rd harmonic ion cyclotron resonance heating were performed on the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)]. A renewed set of nuclear diagnostics was used for analysing fast D ions during sawtooth stabilization, monster sawtooth crashes, and during excitation of Alfvén eigenmodes (AEs) residing inside the q = 1 radius. The measurements and modeling of the fast ions with the nonlinear HAGIS code [S. D. Pinches et al., Comput. Phys. Commun. 111, 133 (1998)] show that monster sawtooth crashes are strongly facilitated by the AE-induced re-distribution of the fast D ions from inside the q = 1 radius to the plasma edge. [ABSTRACT FROM AUTHOR]

Previous studies have shown that obliquely propagating Alfven waves may be excited in the electromagnetic alpha/proton instability. In this paper, two-dimensional hybrid simulations are performed to investigate the nonlinear evolution of the electromagnetic alpha/proton instability. We further find that the obliquely propagating Alfven waves excited by the alpha/proton instability have nearly linear polarization. The background proton component, as well as the alpha component, can be resonantly heated by the oblique Alfven waves. The implications of our results to the unsolved solar coronal hearing problem are also discussed in this paper. [ABSTRACT FROM AUTHOR]

The velocity space diffusion of charged test particles in random magnetostatic fields is re-investigated from a semi-dynamical point of view. The dynamics of charged particles in resonance with parallel propagating electromagnetic waves is investigated numerically and compared with analytical results for the trapping width in velocity space, Δv∥, and the bounce frequency, ωb. It is demonstrated how an understanding of the basic resonance phenomenon can lead to a better understanding of the validity regions of the quasi-linear theory and their implications for numerical simulations. It is shown, using established analytical expressions for Δv∥ and ωb, that the quasi-linear diffusion coefficient can be written in a new physically illuminating form. The concept of an effective trapping width in velocity space for the turbulence modified resonance structure is introduced. It is shown how this effective resonance width implies a condition on the density of wave modes in Fourier space, in the vicinity of the resonant wave number. The implications of this condition for simulations utilizing discrete fields are discussed in detail and examples of simulations violating this condition are presented. Other issues pertinent to the simulation of velocity diffusion in turbulent electromagnetic fields are discussed, paying attention to the discretization of the fields and the temporal discretization of the dynamical equations. [ABSTRACT FROM AUTHOR]

The investigation of the existence of arbitrarily large amplitude electrostatic dust-acoustic double layers is conducted in a four-component plasma consisting of electrons, two distinct positive ion species of different temperatures, and massive negatively-charged dust particles that are assumed spheres of different radii distributed according to a power-law. The dependence of the dust grain charge on its size is considered to be nonlinear. The number densities of electrons and ions are assumed to follow a Boltzmann distribution, whereas the dynamics of charged dust grains is described by fluid equations. Comparison is conducted between plasmas containing size-distributed dust grains and those containing monosize dust grains, while examining the criteria for the existence of dust-acoustic double layers along with the dependence of their amplitudes and Mach numbers on plasma parameters. [ABSTRACT FROM AUTHOR]

To deeply investigate the nonlinear interaction between the sheet beam and the slow wave mode in the dielectric loaded rectangular Cerenkov maser, a third order differential equation of the field profile function is rigorously derived. By combining with the relativistic equation of motion and using the traveling-wave boundary condition, the nonlinear phenomena, which involve with the growth rate, the electron phase bunching, the saturated power and length, etc., can be predicted through numerical calculations. An illustrative example has been given to demonstrate the validation of this method. The results show that a beam with axial momentum spread will lower the saturated power, increase the saturated length, and decrease the working bandwidth. [ABSTRACT FROM AUTHOR]

Weakly nonlinear ion-acoustic (IA) solitary waves, which accompany electronegative plasmas composed of positive ions, negative ions, and nonextensive electrons are investigated. Allowing for electrons departure from Boltzmann's distribution is shown to bear considerable new features of the IA soliton characteristics. Three different types of electronegative plasmas inspired from the experimental studies of Ichiki et al. [Phys. Plasmas 8, 4275 (2001)] are discussed, and the dependence of IA solitons basic characteristics on physical parameters is also investigated. It is found that for certain values of the negative-to-positive ion density ratio, ν, the positive-to-negative ion mass ratio, Q, and the nonextensive parameter, q, the plasma system supports rarefactive solitons. [ABSTRACT FROM AUTHOR]

An electromagnetic (EM) wave at the mode conversion layer transfers its energy to the electrostatic (ES) wave whose amplitude can be greatly enhanced due to its slow group velocity near the cut off layer. The large amplitude ES wave produces the density compression, indispensable for the nonlinear coupling in the EM wave, leading to the localized vortex flow. A dc magnetic field, tantamount to the vorticity, is generated as a result of the conservation of canonical momentum. [ABSTRACT FROM AUTHOR]

Propagation of a laser beam, having radial and axial Gaussian profile, in partially stripped plasma is analyzed. A wave equation, for the laser electric field driven by linear as well as nonlinear contributions due to atoms and plasma electrons, has been set up. A variational technique is used to obtain equations describing the evolution of the laser spot size and pulse length, and numerical methods are used to study their simultaneous evolution in partially stripped plasma. [ABSTRACT FROM AUTHOR]

A model of turbulence intensity spreading with self-consistent nonlinear noise is derived systematically for the simple dynamical model of resistivity gradient driven turbulence. Local effective drive, thermal conduction damping, nonlinear coupling, and spatial scattering effects are included. As a consequence of nonlinear mode coupling processes (i.e., triad mode interactions), turbulence energy can be spatially scattered, leading to turbulence propagation and spreading. However, the range of any nonlinear mode interactions of the background with a test mode is restricted to within a few mode scale widths from the test mode rational surface. The speed of a turbulent spreading front is calculated. This front speed is effectively constant on macroscopic scales. We show that the effect of self-consistent nonlinear noise on the intensity front speed is modest, as a consequence of the ordering Δc

A weakly nonlinear analysis is carried out to investigate the properties of dust ion-acoustic shock waves in a charge varying dusty plasma with vortexlike electron distribution. We use the ionization model, hot ions with equilibrium streaming speed and a trapped electron charging current derived from the well-known orbit limited motion theory. A new modified Burger equation is derived. Besides nonlinear trapping, this equation involves two kinds of dissipation (the anomalous one inherent to nonadiabatic dust charge fluctuation and the one due to the particle loss and ionization). These two kinds of dissipation can act concurrently. The traveling wave solution has been acquired by employing the modified extended tanh-function method. The shocklike solution is numerically analyzed based on the typical numerical data from laboratory dusty plasma devices. It is found that ion temperature, trapped particles, and weak dissipations significantly modify the shock structures. [ABSTRACT FROM AUTHOR]

The effect of collision on small amplitude dust-acoustic waves is investigated for a plasma with positively charged dust grains. Taking into account the presence of different electron populations in thermal equilibrium, a modified Korteweg-de Vries equation is established. The existence conditions and nature of the waves, i.e., rarefactive or compressive, are found to be mainly dependent on the temperature and the density of the cold electrons. The present model is used to understand the salient features of the fully nonlinear dust-acoustic waves in the lower region of the Earth's ionosphere, at an altitude of ∼85 km with the presence of an external heating source. [ABSTRACT FROM AUTHOR]

The nonlinear enhancement of plasma density in a combination of two and four collisional internal inductively coupled plasma sources has been experimentally investigated at different mediate gas pressures and radio-frequency powers, where each source can be considered as independent and the combination is linear. In the nonlinear enhancement phenomenon, the plasma density distribution in combination is not only larger than that of every individual source, but also larger than the linear summation of them in most region of the midplane. The nonlinear enhancement effect in the center of the midplane has stronger functional relation to the plasma density and is sensitive to the arrangement method, while it is weakly affected by the neutral particle density. Meanwhile, the electron temperature approximately keeps constant during the antenna's individual to combinational discharge. Furthermore, a nonlinear diffusion model including the multistep ionization is applied to describe the nonlinear enhancement phenomenon in linear combination, of which the solutions are good consistent with the experimental results. [ABSTRACT FROM AUTHOR]

This paper studies the linear and nonlinear stages of the fan instability, considering electromagnetic waves of the whistler frequency range interacting resonantly with energetic electron fluxes in magnetized plasmas. The main attention is paid to determine the wave-particle interaction processes that can lead to the excitation of intense electromagnetic waves by nonequilibrium particle distributions involving suprathermal tails, and to explain under what conditions and through what mechanisms they can occur, develop, and saturate. This paper presents and discusses two main processes: (i) the linear fan instability and (ii) the nonlinear process of dynamical resonance merging, which can significantly amplify the energy carried by linearly destabilized waves after they saturate due to particle trapping. This study consists of (i) determining analytically and numerically, for parameters typical of space and laboratory plasmas, the linear growth rates of whistlers excited by suprathermal particle fluxes through the fan instability, as well as the corresponding thresholds and the physical conditions at which the instability can appear, (ii) building a theoretical self-consistent 3D model and a related numerical code for describing the nonlinear evolution of the wave-particle system, and (iii) performing numerical simulations to reveal and characterize the nonlinear amplification process at work, its conditions of development, and its consequences, notably in terms of electromagnetic wave radiation. The simulations show that when the waves have reached sufficient energy levels owing to the linear fan instability, they saturate by trapping particles and due to the complex dynamics of these particles in the electromagnetic fields, the resonant velocities' domains of the waves overlap and merge, meanwhile a strong increase of the wave energy occurs. [ABSTRACT FROM AUTHOR]

In this paper, we present our nonlinear kinetic modeling of stimulated Raman scattering in a uniform and collisionless plasma using envelope equations. We recall the derivation of these equations, as well as our theoretical predictions for each of the nonlinear kinetic terms, the precision of which having been carefully checked against Vlasov simulations. We particularly focus here on the numerical resolution of these equations, which requires the additional concept of 'self-optimization' that we explain, and we describe the envelope code BRAMA that we used. As an application of our modeling, we present one-dimensional BRAMA simulations of stimulated Raman scattering which predict threshold intensities, as well as time scales for Raman growth above threshold, in very good agreement with those inferred from Vlasov simulations. Finally, we discuss the differences between our modeling and other published ones. [ABSTRACT FROM AUTHOR]

A fully nonlinear model is developed for the bump-on-tail instability including the effects of dynamical friction (drag) and velocity space diffusion on the energetic particles driving the wave. The results show that drag provides a destabilizing effect on the nonlinear evolution of waves. Specifically, in the early nonlinear phase of the instability, the drag facilitates the explosive scenario of the wave evolution, leading to the creation of phase space holes and clumps that move away from the original eigenfrequency. Later in time, the electric field associated with a hole is found to be enhanced by the drag, whereas for a clump it is reduced. This leads to an asymmetry of the frequency evolution between holes and clumps. The combined effect of drag and diffusion produces a diverse range of nonlinear behaviors including hooked frequency chirping, undulating, and steady state regimes. An analytical model is presented, which explains the aforementioned diversity. A continuous production of hole-clump pairs in the absence of collisions is also observed. [ABSTRACT FROM AUTHOR]

To explain the generation of vortex patterns of dust grains in a magnetized dusty plasma [Huang et al., Plasma Sci. Technol. 9, 1 (2007)], a time dependent nonlinear model that describes vortices as a result of an instability is proposed. Grain-grain as well as grain-ion interactions, particle attachment, and grains drift and diffusion are key elements in the present model. It is found that the latter reproduces the experimental results quite well, whereas the stability analysis shows that the vortex core is grain size dependent. [ABSTRACT FROM AUTHOR]

An analysis of interaction between two temperature electron species in the presence of static neutralizing ion background is presented. It is shown that electron plasma waves can nonlinearly interact with electron acoustic wave in a time scale much longer than ωp-1, where ωp is electron plasma frequency. A set of coupled nonlinear differential equations is shown to exist in such a scenario. Propagating soliton solutions are demonstrated from these equations. [ABSTRACT FROM AUTHOR]

An analytical theory for the interaction of an electron bunch with a nonlinear plasma wave is developed to make it possible to design efficient laser- and/or beam-driven accelerators that generate high quality monoenergetic electron beams. This theory shows how to choose the charge, the shape, and the placing of the bunch so that the conversion efficiency from the fields of the bubble to the accelerating electrons reaches nearly 100% and the beam quality is optimized. For intense drivers the nonlinear wake is described by the shape of the bubble and beam loading arises when the radial space-charge force of the beam acts back on the electron sheath surrounding the ion channel. The modification of the wake due to the presence of flat-top electron bunches is studied and it is shown that the energy spread of an externally injected flat-top electron bunch can be kept low. The bunch profile that leads to zero energy spread is also derived. [ABSTRACT FROM AUTHOR]

A weakly nonlinear analysis is carried out to derive a Korteweg–de Vries Burgers-like equation for small but finite amplitude dust ion-acoustic (DIA) waves in a charge varying dusty plasma with non thermally distributed electrons. The correct expression for the nonthermal electron charging current is used. Interestingly, it may be noted that due to electron nonthermality and finite equilibrium ion streaming velocity, the present dusty plasma model can admit compressive as well as rarefactive DIA solitary waves. Furthermore, there may exist DIA shocks which have either monotonic or oscillatory behavior and the properties of which depend sensitively on the number of fast nonthermal electrons. Our results should be useful to understand the properties of localized DIA waves that may occur in space dusty plasmas. [ABSTRACT FROM AUTHOR]

Experiments in the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)] have yielded new, unique observations of nonlinear three-wave interactions between compressional Alfvén eigenmodes (CAEs) and other fast-ion driven instabilities. Specifically, nonlinear interactions of CAEs have been conclusively identified with both energetic particle modes (EPMs) and toroidicity-induced Alfvén eigenmodes (TAEs). These nonlinear interactions occur simultaneously with other three-wave interactions observed between the TAEs and EPMs [N. A. Crocker et al., Phys. Rev. Lett. 97, 045002 (2006)]. The interaction between the CAEs and EPMs spatially redistributes the energy of the CAEs, concentrating it into a toroidally localized wave packet in the same way that the interaction between the TAEs and EPMs spatially concentrates the energy of the TAEs. The interaction between the CAEs and TAEs has been shown to further subdivide the CAE wave packet into a train of smaller wave packets. These nonlinear interactions occur during fast-ion loss events. The spatial redistribution of CAE fluctuation energy will modify the effect of the CAEs on fast-ion transport during these events. [ABSTRACT FROM AUTHOR]

This paper presents the model equations governing the nonlinear interaction between dispersive Alfvén wave (DAW) and magnetosonic wave in the low-β plasmas (β

Properties of fully nonlinear ion-acoustic solitary waves in a plasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive the energy integral equation with a new Sagdeev potential. The latter is analyzed to examine the existence regions of the solitary pulses. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as the nonthermal electron parameter. Numerical solution of the energy integral equation clears that both positive and negative potentials exist together. It is found that faster solitary pulses are taller and narrower. Furthermore, increasing the electron nonthermality parameter (negative-to-positive ions density ratio) decreases (increases) the localized excitation amplitude but increases (decreases) the pulse width. The present model is used to investigate the solitary excitations in the (H+,O2-) and (H+,H-) plasmas, where they are presented in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the fully nonlinear ion-acoustic solitary waves in space and in laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present. [ABSTRACT FROM AUTHOR]

The collective backscattering of intense laser radiation by energetic electron beams is considered. Exact solutions for the radiation field are obtained, for arbitrary electron pulse shapes and laser intensities. The electron beams act as imperfect nonlinear mirrors on the incident laser radiation. This collective backscattering process can lead to the development of new sources of ultrashort pulse radiation in the gamma-ray domain. Numerical examples show that, for plausible experimental conditions, intense pulses of gamma rays, due to the double Doppler shift of the harmonics of the incident laser radiation, can be produced using the available technology, with durations less than one attosecond. [ABSTRACT FROM AUTHOR]

A quasi-logistic, nonlinear model for ionization wave modes is introduced. Modes are due to finite size of the discharge and current feedback. The model consists of competing coupled modes and it incorporates spatial wave amplitude saturation. The hysteresis of wave mode transitions under current variation is reproduced. Sidebands are predicted by the model and found in experimental data. The ad hoc model is equivalent to a general—so-called universal—approach from bifurcation theory. [ABSTRACT FROM AUTHOR]

The flow of electron and ion conduction currents across a nonlinear capacitive sheath to the electrode surface self-consistently sets the dc bias voltage across the sheath. We incorporate these currents into a model of a homogeneous capacitive sheath in order to determine the enhancement of the Ohmic and stochastic heating due to self-excitation of the nonlinear series resonance in an asymmetric capacitive discharge. At lower pressures, the series resonance can enhance both the Ohmic and stochastic heating by factors of 2–4, with the Ohmic heating tending to zero as the pressure decreases. The model was checked, for a particular set of parameters, by a particle-in-cell (PIC) simulation using the homogeneous sheath approximation, giving good agreement. With a self-consistent Child-law sheath, the PIC simulation showed increased heating, as expected, whether the series resonance is important or not. [ABSTRACT FROM AUTHOR]

It has been shown that a large amplitude Alfvén wave can stabilize linear magnetosonic instabilities triggered by an ion beam. This phenomenon occurs for large amplitude waves above a threshold value. Here the effect of a second ion beam on the threshold amplitude for stabilization of the magnetosonic instability is studied. It is shown that the second beam modifies the threshold amplitude behavior for complete saturation of the magnetosonic instability. The effect of the second beam on the properties of purely electrostatic nonlinear instabilities triggered by the finite amplitude wave is also studied. Apart from the changes induced by the second beam on the threshold amplitude behavior, it is shown that in some cases there are two regimes of the nonlinear ion-acousticlike instability. These results should be of importance in those environments where the interplay of the two beams should not be ignored like, e.g., in the fast solar wind. [ABSTRACT FROM AUTHOR]

In this paper, the efficiency of electron acceleration by a short, powerful laser pulse propagating across an external magnetic field is investigated. Conditions for the decay of a laser pulse with frequency close to the upper hybrid resonance frequency are analyzed. It is also shown that a laser pulse propagating as an extraordinary wave in cold, magnetized, low-density plasma takes the form of a nonlinear wave with the modulated amplitude (envelope soliton). Finally, simulation results on the interaction of an electromagnetic pulse with a semi-infinite plasma, obtained with the help of an electromagnetic relativistic PIC code, are discussed and a comparison with the obtained theoretical results is presented. [ABSTRACT FROM AUTHOR]

Linear and nonlinear gyrokinetic simulations of collisionless magnetic reconnection in the presence of a strong guide field are presented. A periodic slab system is considered with a sinusoidally varying reconnecting magnetic field component. The linear growth rates of the tearing mode in both the large and small Δ′ regimes are compared to kinetic and fluid theory calculations. In the nonlinear regime, focusing on the limit of large Δ′, the nonlinear reconnection rates in the gyrokinetic simulations are found to be comparable to those obtained from a two-fluid model. In contrast to the fluid system, however, for Ti>Te and very small initial perturbation amplitudes, the reconnection in the gyrokinetic system saturates in the early nonlinear phase. This saturation can be overcome if the simulation is seeded initially with sufficient random noise. [ABSTRACT FROM AUTHOR]

The linear and nonlinear properties of the ion-acoustic waves (IAWs) are investigated by using the quantum hydrodynamic equations together with the Poisson equation in a three-component quantum electron-positron-ion plasma. For this purpose, a linear dispersion relation, a Korteweg-de Vries equation and an energy equation containing quantum corrections are derived. Computational investigations have been performed to examine the quantum mechanical effects on the linear and nonlinear waves. It is found that both the linear and nonlinear properties of the IAWs are significantly affected by the inclusion of the quantum corrections. The relevance of the present investigation to dense white dwarfs (where the electron-positron annihilation can be unimportant) is discussed. [ABSTRACT FROM AUTHOR]

Nonlinear drift-kinetic theory is proposed for lower-hybrid solitary structures in near-Earth plasmas, based on a two time scale kinetic description of nonlinear interactions between the lower-hybrid and dispersive Alfvén waves. The detailed derivation of the nonlinear coupling terms in an arbitrary geometry is presented, that include the ponderomotive potential, non-curl-free component of the perpendicular electron velocity, and the electron diffusion in velocity space. It is shown that the resonant particles are trapped by the combined effects of the slow and ponderomotive potentials, and that their density is further modified by their diffusion in velocity space, yielding a new type of coherent structure, which is identified as an electron hole, coupled with a nonlinear Schrödinger-type soliton. A numerical solution is found in the form of train of soliton-like lower-hybrid spikes, trapped inside a weakly two-dimensional slab electron hole. [ABSTRACT FROM AUTHOR]

The nonlinear interaction between two laser beams in a plasma is investigated in the weakly nonlinear and relativistic regime. The evolution of the laser beams is governed by two nonlinear Schrödinger equations that are coupled with the slow plasma density response. A nonlinear dispersion relation is derived and used to study the growth rates of the Raman forward and backward scattering instabilities as well of the Brillouin and self-focusing/modulational instabilities. The nonlinear evolution of the instabilities is investigated by means of direct simulations of the time-dependent system of nonlinear equations. [ABSTRACT FROM AUTHOR]

The convection of dust particles in a plasma is related to the spatial gradients of dust charge distributions existing due to different plasma conditions in different parts of dusty structures. Here, the set of nonlinear equations is derived to describe the dust convective structures appearing as perturbations of the basic nonlinear structures obtained in Part I. On its basis, various cases of the dust convection in cylindrical dusty structures in a plasma are obtained. It is demonstrated that there is the broad range of plasma and dust parameters where the self-organized dust convection exist. [ABSTRACT FROM AUTHOR]

The effect of finite electron mass on the formation and sustainment of a field reversed configuration (FRC) by rotating magnetic fields (RMF) is studied. The importance of inertial effects is measured by the ratio between the RMF frequency (ω) and the electron-ion collision frequency (ν). In the limit where this ratio is very small (ω/ν→0), previous results corresponding to massless electrons are recovered. When ω/ν increases there are significant changes in the value of the minimum external rotating field needed to sustain the FRC and the time required to reach a steady state. Since ν decreases with increasing temperature and decreasing density, these effects are expected to become more important as fusion relevant temperatures are approached. [ABSTRACT FROM AUTHOR]

The basic theory of cross-talking signals between counter-streaming electron beams in a vacuum tube oscillator consisting of two two-cavity klystron amplifiers reversely coupled through input/output slots is theoretically investigated. Application of Kirchhoff’s laws to the coupled equivalent RLC circuit model of the device provides four nonlinear coupled equations, which are the first-order time-delayed differential equations. Analytical solutions obtained through linearization of the equations provide oscillation frequencies and thresholds of four fundamental eigenstates, symmetric/antisymmetric 0/π modes. Time-dependent output signals are numerically analyzed with variation of the beam current, and a self-modulation mechanism and transition to chaos scenario are examined. The oscillator shows a much stronger multistability compared to a delayed feedback klystron oscillator owing to the competitions among more diverse eigenmodes. A fully developed chaos region also appears at a relatively lower beam current, ∼3.5Ist, compared to typical vacuum tube oscillators (10-100Ist), where Ist is a start-oscillation current. [ABSTRACT FROM AUTHOR]