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The precessional fishbone instability is an m = n = 1 internal kink mode destabilized by a population of trapped energetic particles. The linear phase of this instability is studied here, analytically and numerically, with a simplified model. This model uses the reduced magneto-hydrodynamics (MHD) equations for the bulk plasma and the Vlasov equation for a population of energetic particles with a radially decreasing density. A threshold condition for the instability is found, as well as a linear growth rate and frequency. It is shown that the mode frequency is given by the precession frequency of the deeply trapped energetic particles at the position of strongest radial gradient. The growth rate is shown to scale with the energetic particle density and particles energy while it is decreased by continuum damping.

This paper investigates the stability of an axisymmetric pancake vortex with Gaussian angular velocity in radial and vertical directions in a continuously stratified-rotating fluid. The different instabilities are determined as a function of the Rossby number $Ro$, Froude number $F_{h}$, Reynolds number $Re$ and aspect ratio ${\it\alpha}$. Centrifugal instability is not significantly different from the case of a columnar vortex due to its short-wavelength nature: it is dominant when the absolute Rossby number $|Ro|$ is large and is stabilized for small and moderate $|Ro|$ when the generalized Rayleigh discriminant is positive everywhere. The Gent–McWilliams instability, also known as internal instability, is then dominant for the azimuthal wavenumber $m=1$ when the Burger number $Bu={\it\alpha}^{2}Ro^{2}/(4F_{h}^{2})$ is larger than unity. When $Bu\lesssim 0.7Ro+0.1$, the Gent–McWilliams instability changes into a mixed baroclinic–Gent–McWilliams instability. Shear instability for $m=2$ exists when $F_{h}/{\it\alpha}$ is below a threshold depending on $Ro$. This condition is shown to come from confinement effects along the vertical. Shear instability transforms into a mixed baroclinic–shear instability for small $Bu$. The main energy source for both baroclinic–shear and baroclinic–Gent–McWilliams instabilities is the potential energy of the base flow instead of the kinetic energy for shear and Gent–McWilliams instabilities. The growth rates of these four instabilities depend mostly on $F_{h}/{\it\alpha}$ and $Ro$. Baroclinic instability develops when $F_{h}/{\it\alpha}|1+1/Ro|\gtrsim 1.46$ in qualitative agreement with the analytical predictions for a bounded vortex with angular velocity slowly varying along the vertical.

A possible new mechanism for anomalous ion heating in ultra-intense laser plasmas is considered here. This mechanism is based on the excitation of an electron two-stream instability that is driven by the fast electron beam and resonantly decays into ion-acoustic waves. These low frequency waves are then strongly damped by the ion collisions in the dense plasma. The model gives a simple explanation for the preferential heating of the bulk ion population observed in recent laser experiments in the petawatt (PW) regime. © 2005 IOP Publishing Ltd.

Dispersion characteristics have been analysed for field-aligned electron–cyclotron waves (also known as right-hand polarized waves, extraordinary waves or whistlers) in a cylindrical magnetic mirror plasma including electrons with anisotropic temperature. It is shown that the instability of these waves is possible only in the range below the minimal electron–cyclotron frequency, which is much lower than the gyrotron frequency used for electron–cyclotron resonance power input into the plasma, under the condition where the perpendicular temperature of the resonant electrons is larger than their parallel temperature. The growth rates of whistler instability in the two magnetized plasma models, where the stationary magnetic field is either uniform or has a non-uniform magnetic mirror configuration, are compared.

The analysis of non-neutral plasmas using fluid models in general implies on the resolutions of coupled differential equations, in particular the so-called rigid-rotor plasma equilibrium involves the solution of the Poisson-Ampere and moment equations. The present work shows an analytical solution for this model at a relativistic cold adiabatic plasma approximation considering a two species plasma where electric field gives an important contribution for the plasma confinement. According to the present study the most important plasma parameters responsible for confinement are the particles angular velocities, as expected, and mass ratio between the species.

An analytical weakly nonlinear model of Benjamin–Feir instability of a Stokes wave on nonuniform unidirectional current is presented. The model describes evolution of a Stokes wave and its two main sidebands propagating on a slowly-varying steady current. In contrast to the models based on versions of the cubic Schrodinger equation the current variations could be strong, which allows us to examine the blockage and consider substantial variations of the wave numbers and frequencies of interacting waves. Interaction with countercurrent accelerates the growth of sideband modes on a short spatial scale. An increase in initial wave steepness intensifies the wave energy exchange accompanied by wave breaking dissipation, results in asymmetry of sideband modes and a frequency downshift with an energy transfer jump to the lower sideband mode, and depresses the higher sideband and carrier wave. Nonlinear waves may even overpass the blocking barrier produced by strong adverse current. The frequency downshift of the energy peak is permanent and the system does not revert to its initial state. We find reasonable correspondence between the results of model simulations and available experimental results for wave interaction with blocking opposing current.

Plasmas in Hall thrusters are typically in regimes where the electron motion across the magnetic is strongly constrained by the Lorentz force and the ion Larmor radius is large so the ions are only weakly affected by the magnetic field. Such plasmas support lower-hybrid and ion-sound modes. In the presence of the ExB electron drift, these modes are easily destabilized by plasma and magnetic field gradients, electron collisions, ion flows, resonance and finite length effects. Interaction of these various effects create a complex picture of turbulence in such plasmas. We analyze these destabilization mechanisms in application to typical conditions of Hall thrusters and discuss their roles in anomalous transport and structure formation. The fluid model of plasma dynamics in these conditions has been developed and numerically implemented in the BOUT++ framework. Wave-particle resonant interaction effects have also been included via the kinetic closures implemented via non-Fourier representation. Results of numerical simulations with this model will be presented in this talk. It is shown that the lower-hybrid instability growth rate is maximized at the wavelength on the order of the electron Larmor radius. In the large wavelength region, formation of coherent large scale structures is observed in the simulations. The relative role of the inherent large scale instability (Simon-Hoh) and the inverse energy cascade (from small to large scales) is being investigated.

When an intense relativistic electron beam propagates through the plasma background, the electron beam can expel the plasma electrons and leave the plasma ions which can be seen as static. In this process, the ion channel can be formed and the electromagnetic radiation can be observed. This paper uses the method called particle-in-cell to study on the influence of different valence state under same particles on electromagnetic radiation in beam-plasma system.

The energy gain of an electron beam in the laser-driven plasma wave can be limited by dephasing between the accelerated electron bunch and the plasma wave. The dephasing length is defined as the length the electrons travel before it phase slip by one-half period of plasma wave. Since the velocity of the accelerated electrons is higher than the phase velocity of plasma wave, the electrons outrun the plasma wave and moves into decelerating region of the plasma wave phase space. In order to enlarge the dephasing length, the plasma wavelength should be increased by optimizing the plasma density profile. We report the measurements of dephasing length using plasma density distribution with linear, up-ramp and parabolic profile. The accelerated electron energy gain is calculated in different plasma density profiles. We observe that the plasma wavelength decreases when the plasma wave propagates from low to high-density layer. After density transition, the accelerated electron phase synchronizes with the phase of plasma wave. This increases the electron acceleration length and improves the beam quality. This may be crucial to determine the electron beam energy in LWFA.

During the disruption scenario in plasma, eddy and halo currents are considered to be the most important sources that come out as a result of this phenomenon1. The components that affects primarily are diverter, First Wall (FW) and other main components because plasma is unstable in vertical displacement. In this scenario, plasma moves upward and downward resulting into plasma disruption and as a result, halo current is generated helically. This halo current produced in SOL component and flows into the vacuum vessel through in-vessel components that may give rise to large force acting on the vessel and in-vessel components. In EAST reactor, some sensors have been installed for calculating the halo currents at different locations. In these experiments, it has been shown that the halo current first spread out on outer baffle plate then moves to dome and finally return back to plasma. In this paper, theoretical model for calculating sideways force in vacuum vessel is developed and verified by experimental data from EAST Tokamak. The proposed innovative system allows an effective way to study the interaction forces with plasma under controlled conditions. We used magnetic field transformation method to calculate the plasma energy in different cross section in different degrees that shows plasma interacting forces including vertical and horizontal2. In this paper, we approached to observe the magnitude of the maximum observed sideways forces at EAST that causes asymmetric loads during VDEs. This work attains novelty as no theoretical calculations for plasma sideways force has been reported so far and this is the first time to used theoretical approach. A Matlab program was developed that has been verified by using experimental data from EAST. The main objective of the research is to established theoretical relation with experimental results so as to precautionary evaluate the plasma behavior in any Tokamak.

When plasma interacts with a surface, a plasma sheath forms at the interface, which is typically a region of net positive space charge. Ions, accelerated by the electric field in the sheath region, and hot electrons are known to cause emission from the surface. This can have consequences for devices such as Hall thrusters as electron emissions can increase the rate of erosion of the electrodes affecting performance and longevity of the thrusters — an important concern for space-bound missions. The length-scale of sheaths is small in comparison to the undisturbed plasma (on order of the Debye length, λD) yet the sheath has a global effect on plasma and needs to be included self-consistently in computer simulations. This usually means resolving the Debye length and the plasma oscillation frequency, which makes global and complex simulations extremely demanding in terms of the computational cost.

Hall plasma devices operate in the regimes when the electrons are magnetized and ions are not. In these conditions standard drift waves due to the plasma density gradient do not exist however another mode appears as a result of the combined response of the inertia of un-magnetized ions and electron drift. This mode is destabilized by the ExB electron drift due to the equilibrium electric field: this is the collisionless Simon-Hoh instability. The local theory predicts that the condition 4ω∗ωE > k⊥2Cs2 is required for the instability, ω∗ and ωE are the electron drift frequency and frequency of the equilibrium ExB drift, respectively; k⊥ is the wave-vector perpendicular to the magnetic field, and Cs is the ion sound velocity. We investigate stability of this mode in general case with spatial profiles of ω∗ and ωE when the local theory is not applicable. The stability of nonlocal modes in slab and cylindrical geometry are investigated numerically with Chebyshev spectral method. The results of theoretical analysis are compared with experimental results from Penning and Hall thruster experiments in an attempt to identify the source of large scale structures in these discharges.

In the fluid-Maxwell theory of the two-plasmon decay instability, when Landau damping is neglected, configuration of plasma waves is described by a hyperbola-lemniscate curve in a wave vector space.1 A point on the curve is determined from density and temperature of a plasma and describes configuration of waves for maximum growth of the instability. However, when a weak Landau damping is taken into consideration, we find a significant deviation of the wave vector from the hyperbola-lemniscate curve, although the known expression for growth rate is preserved. Here we present a perturbation expansion of the growth rate from the hyperbola configuration, using the angle variable of wave vector of a plasma wave. And analysis for configuration of waves for maximum growth rate produces an implicit algebraic equation for the angle variable. An example numerical solution of the equation shows 65.5° rather than the well-known 45” inclination from the pump direction.

When the duration of laser pulse is comparable to the plasma wave period, the large-amplitude plasma wave can be driven by the laser. In the presence of a guiding magnetic field, the large-amplitude plasma wave of finite transverse extent and large phase velocity resonantly accelerates the electrons to a higher energy-level. For a small laser spot size the laser exerts an axial as well as the radial ponderomotive force on the electrons that creates a density depression on the laser axis. This electron depleted channel also creates a radial electric field (ion space-charge field). Acceleration of electrons in this channel is investigated, where the effect of ion space-charge field is considered, by solving the dynamical equations using a two-dimensional particle-in-cell code for particle acceleration. We observe that the spacecharge field plays an important role in electron energy gain during acceleration by a plasma wave in a magnetic plasma channel.

The plasma inside a Hall thruster is a complex environment full of instabilities and interesting physical phenomena such as anomalous transport. To better understand this complex plasma dynamics, a nonlinear fluid model has been developed. The model contains the effect of electron inertia, electron collisions, electron temperature and density gradients as well as nonlinearities in the ion velocity and the electron advection term that arises from the ExB drift. The model is simulated using BOUT++, a framework for plasma simulations developed at the Lawrence Livermore National Laboratory. The linear limits of the model correspond to the lower hybrid mode rendered unstable by collisions and to the density gradient drift instabilities.

Spatio-temporal evolution of relativistic Buneman instability has been investigated in one dimension using a particle-in-cell simulation code. Starting from the excitation of the instability, its evolution has been followed numerically till its quenching and beyond. It is found that the maximum growth rate(γmax) reduces due to relativistic effects and varies with γe0 and m/M as γmax ∼ √(3/4γe0) (m/2M)1/3, where γe0 is Lorentz factor associated with the initial electron beam velocity(vo) and (m/M) is the electron to ion mass ratio. Further it is observed that in contrast to the non-relativistic results1,2 at the saturation point, ratio of electrostatic field energy density (E2/8π) to the initial drift kinetic energy density (W0) scales with γe0 as ∼1/γ2e0. These results are found to be in good agreement with that derived using fluid theory.

Operation of a number of plasma devices such as Hall thrusters for electric propulsion and magnetrons for plasma processing rely on ExB drift of electrons in crossed electric and magnetic fields. The closed drift of electrons supports plasma ionization. The magnetic field constrains electron motion in perpendicular direction, while ions can be freely accelerated and extracted by the electric field from the discharge and used for various purposes such as thrust for electric propulsion, material deposition and modification for plasma processing. The electron current is also a source of free energy resulting in a number of discharge instabilities. In all, it is important to accurately predict the electron drift velocity and electron current. Large fraction of the electron current is due to the ExB drift. In a plasma with finite temperature the contribution of diamagnetic velocity due to inhomogeneous plasma pressure becomes important and comparable (for typical parameters) to the ExB drift. The magnetic gradient and curvature drifts existing in guiding center theory do not contribute additional current unless the plasma pressure is anisotropic. The structure and various contributions to the total electron current in inhomogeneous plasma and inhomogeneous magnetic field are discussed for some typical parameters of Hall devices.

Results are presented from basic heat transport experiments and gyrokinetic simulations of multiple magnetized electron temperature filaments in close proximity. This arrangement samples cross-field transport from nonlinear drift-Alfven waves and large scale convective cells. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A biased LaB6 cathode injects low energy electrons (below ionization energy) along a strong magnetic field into a pre-existing large and cold plasma forming an electron temperature filament embedded in a colder plasma, and far from the machine walls. A car bon masking plate with several holes (each 1cm diameter, 1.5 cm apart) is used to create 3 electron temperature filaments. By covering two holes in the mask drift-Alfven and thermal waves from a single filament have been characterized and compared to previous studies with a different electron beam source1. The observed eigenmode structures also compares favor ably with recent 3D gyrokinetic simulations2. The 3-filament case exhibits a complex wave pattern and enhanced cross-field transport. Detailed mode analysis and comparison with non linear simulations is reported.

The problem of Jeans gravitational instability and radiative instability is investigated for partially ionized self-gravitating plasma which has connection in astrophysical condensations and formation of objects. A general dispersion relation has been derived with the help of relevant linearized perturbation equations, using the normal mode analysis method. Effects of FLR corrections, radiative heat-loss function and collisions with neutrals on the Jeans criterion of self-gravitational instability of the system are discussed. The conditions of instability are derived for a temperature-dependent and density-dependent heat-loss function with thermal conductivity and FLR corrections for some special case. The stability of the system is discussed by using Routh-Hurwitz’s criterion. Numerical calculations have been performed to discuss the dependence of the growth rate of the Jeans gravitational instability on the various physical parameters. The FLR corrections, viscosity, porosity, magnetic field, and neutral collision have stabilizing influence while finite electrical resistivity and permeability have a destabilizing influence on the growth rate of the gravitational instability. Our results are helpful for understanding the formation of dense molecular clouds.

The Richtmyer-Meshkov instability (RMI) mixing flow induced by a planar shock wave of Mach 1.6 is investigated using direct numerical simulation method. Interfacial perturbations of different scales between air and sulfur hexafluoride are introduced to study the effect of the initial conditions. Focus is placed on the analysis of the scale-to-scale transfer of kinetic energy in both Fourier and physical spaces. The kinetic energy injected from the perturbation scales is transferred to both larger and smaller scales in an average sense within the inner mixing zone (IMZ) at early times and is mainly passed down into smaller scales at the late stage. The physical-space energy flux due to the subgrid-scale (SGS) stress is studied using a filtering approach in order to shed light on the physical origin of the scale-to-scale kinetic energy transfer. It is found that the pointwise SGS energy flux is highly correlated with the local spike and bubble structures in the IMZ. Moreover, it turns out that the mean SGS energy flux is mainly ascribed to the component in the direction of shock wave propagation. An analysis using the method of conditional averaging manifests that the generation of local SGS energy flux is associated with the property of the surrounding flow induced by quadrupolar or dipolar vortex structures.

THz radiation straddles the microwave and infrared bands of the electromagnetic spectrum, thus combining the penetrating power of lower-frequency waves and imaging capabilities of higher-energy infrared radiation. THz radiation is employed in various elds such as cancer research, biology, agriculture, homeland security, and environmental monitoring. Conventional vacuum electronic sources of THz radiation (e.g., fast- and slow-wave devices) either require very small structures or are bulky and expensive to operate. Optical sources necessitate cryogenic cooling and are presently capable of producing milliwatt levels of power at THz frequencies. We propose a millimeter and sub-millimeter wave source based on a well-known phenomenon called the two-stream instability. The two-beam source relies on lowenergy and low-current electron beams for operation. Also, it is compact, simple in design, and does not contain expensive parts that require complex machining and precise alignment. In this dissertation, we perform 2-D particle-in-cell (PIC) simulations of the interaction region of the two-beam source. The interaction region consists of a beam pipe of radius ra and two electron beams of radius rb co-propagating and interacting inside the pipe. The simulations involve the interaction of unmodulated (no initial energy modulation) and modulated (energy-modulated, seeded at a given frequency) electron beams. In addition,more » both cold (monoenergetic) and warm (Gaussian) beams are treated.« less

In the present work we have studied the novel nonlinear phenomenon of plasma physics - beam-plasma instability in a charged plasma in the absence of ions. We have shown the possibility of the instability development and analyzed the characteristics of physical processes taking place during the beam-plasma interaction.

A generalized hydrodynamic model is used to analyse the growth rate of the Jeans instability of a partially ionized strongly coupled plasma incorporating the effects of rotation and Hall current. The general dispersion relation is determined for the propagation of magnetohydrodynamic waves using the normal mode analysis theory. The general dispersion relation is further discussed in four different combinations of rotation and propagation of the system to signify the importance of rotation and neutral particles on the growth rates and conditions of Jeans instability in hydrodynamic and kinetic regimes. The different types of waves are also described in these cases. The influence of rotation and neutral particles on growth rate of the Jeans instability is analysed numerically and shown graphically. The possible applications of the present work are found in ultracold neutral plasmas, white dwarfs, neutron stars etc.

Electro magnetic-wave propagation through equilibriu m p lasmas can lead to med iu m instabilities whose formation and growth conditions are of importance to study. Raman forward scattering (RFS) instability in low-density plasma s is investigated through particle-in-cell (PIC) simu lation, which is employed due to plasmas' high complexity, costly experiment process, and nonlinear behavior in physical terms. A 2D electro magnetic PIC code is used to model RFS instability. Do ing so, a plasma mediu m containing ions and electrons is PIC simulated and ions are assumed to form a constant background because of high inertia. The results indicate that as a plane electro magnetic wave enters the plasma med iu m, large -amp litude longitudinal waves, whose growth rate is well consistent with the theoretical results, begin to grow, suggesting the appearance of RFS instability.

The processes of heating and acceleration of plasma in current sheets formed in 2D and 3D magnetic configurations with an X-line in helium plasma have been investigated using spectroscopic methods. It is found that, in 2D magnetic configurations, plasma flows with energies of 400–1000 eV, which are substantially higher than the ion thermal energy, are generated and propagate along the width (the larger transverse dimension) of the sheet. In 3D configurations, the influence of the longitudinal (directed along the X-line) component of the magnetic field on the plasma parameters in the current sheet has been studied. It is shown that plasma acceleration caused by the Ampere force can be spatially inhomogeneous in the direction perpendicular to the sheet surface, which should lead to sheared plasma flows in the sheet.

Modulation instability of an intense right-hand elliptically polarized laser beam propagating through an electron–positron plasma is investigated by a new method. The nonlinear dispersion relation, in which the relativistic and ponderomotive nonlinearities are taken into account, is obtained for the laser radiation in electron–positron plasma by the Lorentz transformation. The Karpman equation is generalized to the case of three dimensions with three field components. When the nonlinear frequency shift of the electromagnetic field in plasma is involved, the nonlinear evolution equation for the slowly varying envelope of the laser field is obtained. Thus, modulation instability of the intense laser beam in electron–positron plasma is studied and the temporal growth rate of the instability is derived. The analysis shows that the growth rate of modulation instability is increased significantly near the critical surface in a laser-plasma.

A dense plasma focus is being studied as a source of fusion neutrons. Lee and Serban noticed ( IEEE Trans. Plasma Sci., vol. 24, no. 3, pp. 1101-1105, 1996) that neutron-optimized Mather-type plasma foci have an almost constant drive parameter I0/(a√(ρ0)). The origin of this parameter goes back to the 1960s. Recently, it has been pointed out that the constant value of the drive parameter means almost the same values of axial and radial velocities, ion temperatures, Alfven velocities, and magnetic energy per unit mass. Several physical mechanisms were suggested to explain the constant characteristic velocities in plasma foci. This paper presents the relation between the drive parameter and the rise rate of a current. The dependence of the drive parameter on plasma focus geometry is also derived. The obtained results are illustrated by neutron-optimized plasma foci with significantly higher drive parameters. Possible consequences on plasma focus research are mentioned.

The problem of radiative instability of homogeneous rotating partially ionized plasma incorporating viscosity, porosity, and electron inertia in the presence of a magnetic field is investigated. A general dispersion relation is obtained using normal mode analysis with the help of relevant linearized perturbation equations of the problem. The modified Jeans criterion of instability is obtained. The conditions of Jeans instabilities are discussed in the different cases of interest. It is found that the simultaneous effect of viscosity, rotation, finite conductivity, and porosity of the medium does not essentially change the Jeans criterion of instability. It is also found that the presence of arbitrary radiative heat-loss function and thermal conductivity modified the conditions of Jeans instability for longitudinal propagation. It is found that, for longitudinal propagation, the conditions of radiative instability are independent of magnetic field, viscosity, rotation, finite electrical resistivity, and electron inertia, but for the transverse mode of propagation it depends upon finite electrical resistivity and strength of magnetic field and is independent of viscosity, electron inertia, and rotation. From the curves we find that viscosity has a stabilizing effect on the growth rate of instability but the thermal conductivity and density-dependent heat-loss function has a destabilizing effect on the instability growth rate.

A three-dimensional (3-D) transient model has been developed to investigate plasma deformation driven by a magnetic field and its influence on arc stability in a circuit breaker. The 3-D distribution of electric current density is obtained from a current continuity equation along with the generalized Ohm's law; while the magnetic field induced by the current flowing through the arc column is calculated by the magnetic vector potential equation. When gas interacts with an arc column, fundamental factors, such as Ampere's law, Ohm's law, the turbulence model, transport equations of mass, momentum and energy of plasma flow, have to be coupled for analyzing the phenomenon. The coupled interactions between arc and plasma flow are described in the framework of time-dependent magnetohydrodynamic (MHD) equations in conjunction with a K-? turbulence model. Simulations have been focused on sausage and kink instabilities in plasma (these phenomena are related to pinch effects and electromagnetic fields). The 3-D simulation reveals the relation between plasma deformation and instability phenomena, which affect arc stability during circuit breaker operation. Plasma deformation is the consequence of coupled interactions between the electromagnetic force and plasma flow described in simulations.

Electrical and spectroscopic investigations of an atmospheric-pressure plasma jet ( APPJ) using variable flow rates of helium gas have shown that an alteration of the gas flow rate changes the operation region of stable uniform discharges. By decreasing the gap spacing to values below 400 μm and decreasing the gas flow rate, the uniform discharges can be operated at higher current densities and, consequently, higher radio-frequency power. Time-resolved optical emission spectroscopy has shown that, at low gas flow rates in narrow gaps (below 400 μm), back diffusion is prominent, which influences the stability of the discharge in the jet. An attempt for scaling up an APPJ by doubling its surface area has shown that, with increasing the surface area, the power dissipation cannot be increased, thus limiting the possibility to scale up such type of plasma sources.

Multidirectional optical diagnostics combined with fast Fourier transform analysis yielding frequency spectra were used for investigations of oscillation phenomena in a thermal plasma jet on various frequencies. The results show that oscillation amplitude distributions in the plane perpendicular to the jet axis depend on the frequency value and, for some frequencies, are strongly asymmetrical. This phenomenon affects the mean distribution of instabilities in a different way, depending on the frequency range. Instantaneous instability distributions are influenced by the phase of arc-current low-frequency modulation.

Theoretical investigation has been made to study the envelope excitations of ion-acoustic solitons (IAS) in plasma composed of electrons, positrons, ions and dust particles. A nonlinear Schrodinger equation which describes the modulational instability of the IAS is derived by using the multiple scale method. The dispersive and nonlinear coefficients are obtained which depend upon the temperature of the ions, concentration of the positrons, electrons and dust particles. The modulationally stable and unstable regions are studied numerically for a wide range of parameters. It is found that these parameters play significant role in the formation of bright and dark envelope solitons in this plasma system.

In this paper we will investigate the effect of two-stream instability on saturation mechanism in Two-Stream Free Electron Laser (TSFEL) with a helical wiggler pump. A two-velocity relativistic electron beam propagates through the helical wiggler field. The relativistic electron stream is assumed to be cold. The slippage of the electromagnetic wave with respect to the electron beam is ignored. Self-consistent evolution of an electromagnetic wave in the presence of two-velocity electron beam is described by a set of coupled nonlinear differential equations in 1D approximation. Slowly varying envelope approximation is used and by the Runge–Kutta method algorithm is solved numerically. The power versus the axial distance has been plotted. It has been found that the TSFEL reaches the saturation regime in a shorter axial distance in comparison with the conventional FEL.

The paper examines the ballooning instability in gyrokinetic approximation taking into account the effects of finite-β, magnetic field line curvature, and diamagnetic drift. We used a simple model with a constant curvature of magnetic field lines which enabled us to obtain analytical results. The possible plasma oscillatory modes comprise the poloidal Alfven and drift compressional modes, coupled due to the magnetic field line curvature and plasma inhomogeneity. The frequencies of these modes depend on the westward current value. As this value grows, the frequencies of these two branches approach to each other, and the branches are merged at some critical value of the current. Then an instability develops which is called the drift ballooning coupling instability. There are three major differences of the drift ballooning coupling instability from the ordinary MHD ballooning instability: (1) the drift ballooning coupling instability is not aperiodic, there is a real part of the oscillation frequency of the order of the drift frequency, (2) only the mode with the same direction of the azimuthal phase speed as the velocity of the ion diamagnetic drift can be unstable, (3) the instability threshold depends on the diamagnetic drift frequency.

In this paper the effect of different parameters like magnetic field, homogenous direct-current electric field, shear scale length, temperature anisotropy, inhomogeneity in direct-current electric field and density gradient on ions velocity is discussed. A mathematical model for ions/micron size particles velocity is discussed and its values are calculated by taking experimental parameters and by applying computer technique. A model of plasma spray machine is also suggested, which contains plasma production with velocity shear instability in laboratory, powder injection and mass and momentum transfers between particles. The coating process by means of velocity shear instability in plasma has possibility to spray hard and arduous material (alloy) with minimum defects and maximum technical and economic efficiency.

To appear in Laser and Particle Beams.; International audience; The out-of-equilibrium situation in which an initially sharp-edged cylindrical electron beam, that could e.g. model electrons flowing within a wire, is injected into a plasma is considered. A detailed computation of the subsequently produced magnetic field is presented. The control parameter of the problem is shown to be the ratio of the beam radius to the electron skin depth. Two alternative ways to address analytically the problem are considered: one uses the usual Laplace transform approach, the other one involves Riemann's method in which causality conditions manifest through some integrals of triple products of Bessel functions.

The paper considers a model problem of instability wave generation that occurs at a tangential discontinuity leaving the edge of a half-plane because of a specially adjusted external action, which models the basic characteristics of an active action on a jet by means of small-size actuators. The dependence of the instability wave amplitude on both the degree of spatial boundedness of the external action and its position with respect to the edge is investigated.

The electron–hole two-stream instability in a quantum semiconductor plasma has been studied including electrons and holes quantum recoil effects, exchange-correlation potentials, and degenerate pressures of the plasma species. Typical values of GaAs and GaSb semiconductors are used to estimate the growth rate of the two-stream instability. The effects of electron– and hole–phonon collision, quantum recoil effects, the streaming velocities, and the corresponding threshold on the growth rate are investigated numerically. Considering the phonon susceptibility allows the acoustic mode to exist and the collisional instability arises in combination with drift of the holes.

The results of the instability investigations of the electrically neutral relativistic plasma flow, consisting of protons and electrons, moving in vacuum at a constant velocity, are described in the paper. The calculations are provided within the framework of Maxwell-Vlasov equations on a three-dimensional (3D) model and the following result is obtained: to a certain time moment t 0, the kinetic energy of protons is almost uniformly redistributed between protons, electrons, and the electromagnetic field that has emerged by this moment. In the 1D calculations the solution is stable.

In experimental investigations array, helical and spiral patterns of a plasma column are formed by changing the operating parameters e.g., input power, working pressure, drive frequency, diameter of the glass tube, background gases, etc. Further, theoretical formulations are attempted using a hydrodynamic model to explain the bifurcation of a plasma column in the transverse and longitudinal axis considering two-step ionization in surface wave produced plasma. Findings of this study reveal that metastable atoms provide two-step ionization which in turn excites weak instability, which bifurcate plasma column in such a way that different patterns are formed.

Low-frequency electromagnetic waves propagating perpendicular to the gradients of the density and magnetic field in an inhomogeneous dusty plasma whose mass density is determined primarily by the dust component are analyzed. It is shown that, in analyzing the dispersion properties of inhomogeneous plasma, it is important to take into account the dynamic properties of ions in the vicinity of the dust-ion hybrid resonance. The conditions for the onset of instability of a magnetic drift wave are investigated for different relations between parameters of the inhomogeneity and the value of the Alfven velocity. The differences from the previous results, as well as possible astrophysical applications, are discussed.

Relativistic effects on the linear and nonlinear properties of electron plasma waves are investigated using the one-dimensional quantum hydrodynamic (QHD) model for a two-component electron–ion dense quantum plasma. Using standard perturbation technique, a nonlinear Schrodinger equation (NLSE) containing both relativistic and quantum effects has been derived. This equation has been used to discuss the modulational instability of the wave. Through numerical calculations it is shown that relativistic effects significantly change the linear dispersion character of the wave. Unlike quantum effects, relativistic effects are shown to reduce the instability growth rate of electron plasma waves.

Stability of a plasma configuration consisting of a thin onedimensional current sheet embedded into a twodimensional background current sheet is studied. Drift modes developing in plasma as unstable waves along the current direction are considered. Dispersion relations for kink and sausage perturbation modes are obtained depending on the ratio of parameters of thin and background current sheets. It is shown that the existence of the background sheet results in a decrease in the instability growth rates and a significant increase in the perturbation wavelengths. The role of drift modes in the excitation of oscillations observed in the current sheet of the Earth's magnetotail is discussed.

Modulational instability of high frequency surface waves on a plasma half-space is investigated taking into account finite temperature effects. The second harmonic generated through nonlinear self-interaction of the waves is found to carry a fraction of the surface wave energy into the bulk of the plasma. This is found to influence the modulational instability mechanism. To describe the nonlinear evolution of the wave, a nonlinear Schrodinger equation is derived in which the coefficient of the nonlinear term becomes a complex quantity. From this evolution equation we derive the condition of instability and show that high-frequency surface waves on a warm plasma half-space are modulationally unstable.

An approach to the enhancement of Cherenkov radiation source driven by two electron beams (TEBs) is presented in this paper. The Cherenkov radiation source is composed of a cylindrical grating, and TEBs with a velocity separation are concentric and separated. By a field matched method, the dispersion equation is derived with a linearized fluid theory and solved by numerical calculation. The numerical results show that a considerable enhancement of growth rate is realized at an optimized voltage ratio due to two stream instability. Moreover, with a help of 2-D particle-in-cell simulations, the improvement of output power induced by the two stream instability is demonstrated, and the decreased of output power is observed as the increased distance of two electron beams.

A three-dimensional (3D) model of the interaction of laser radiation with plasma in the framework of Maxwell-Vlasov equations has been used to calculate the anomalous optical absorption in plasma of supercritical density. The results of calculations confirmed the development of anomalous absorption that was previously revealed by 2D models, which were insufficient for comparison to the experiment. Calculations were performed for a system containing about 106 macroparticles that allowed the absorption coefficient and other characteristics of anomalous absorption in plasma with an inhomogeneous surface to be determined as functions of various parameters of the incident radiation and plasma target. Results are analyzed and estimations are obtained for the contributions of ionization processes and pair collisions of electrons, which show that these factors were quite reasonably ignored in the model. All quantitative results are obtained for the third harmonic of neodymium laser (λ = 0.351 μm) at a tenfold excess of the substance density over a critical value for this radiation.

A new type of beam discharge, i.e., beam discharge with a distributed virtual cathode (VC) is proposed and considered by numerical simulation. The discharge is established during counter motion of high-current electron beams in a gas-filled equipotential cavity and is characterized by a state of hot dense electron plasma of primary electrons. The discharge temporal dynamics is studied. It is shown that the VC lifetime depends linearly from this sum in a wide range of the sum of beam currents, from the boundary current of two-beam instability to the critical current of Pierce instability. Generation of nonlinear electrostatic structures shaped as phase bubbles in the discharge is detected, and their dynamics is studied. The parameters are determined, at which the multiple coexistence of phase bubbles and their coalescence during collisions is observed.

One dimensional Particle in Cell simulations of a dust- dust counter-streaming instability in a plasma containing dust grains of opposite charge polarity are presented. This dust-dust instability has potentially the lowest threshold drift for a dust wave instability in an unmagnetized dusty plasma. The linear and nonlinear development of the dusty plasma instability is investigated, including the effects of collisions with background neutrals, and a background electric field which acts as a driver to impart the drift velocities of the counter streaming charged dust particles. The saturation of the linear instability appears to be dust heating related to dust trapping. Potential double layer formation from dust-dust turbulence is observed in cases with a high neutral collision rate. A comparative study is done with varying collision rates and background electric fields to explore the nonlinear development as a function of collision rate and background electric field. These simulation results could help guide future laboratory and micro-gravity dusty plasma experiments on this instability. The results could also relate to similar counter-streaming instabilities in pair plasmas and negative ion plasmas

Electromagnetic radiation from an anisotropic plasma slab formed by ionization of matter in the field of a high-power femtosecond pulse is studied. It is shown that the growth of initial field perturbations in the course of Weibel instability is accompanied by the generation of nonmonochromatic radiation with a characteristic frequency on the order of the instability growth rate. It is found that perturbations with characteristic scale lengths less than or on the order of the ratio of the speed of light to the Langmuir frequency are excited and radiated most efficiently, provided that the slab is thicker than this ratio.