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A nonlocal theory of Weibel and two stream instabilities of a relativistic electron beam of finite width propagating through a plasma, is developed. The beam pushes a fraction of the plasma electrons out of the beam region and imparts the residual electrons return velocity. The relative drift between the beam and plasma electrons drives an electromagnetic perturbation with quantized transverse wave vector, causing Weibel instability. The system is also unstable to electrostatic perturbation of finite parallel wave vector (parallel to beam velocity). For typical parameters the growth rate of the instability acquires values comparable to a fraction of the plasma frequency.

We report experimentally observed triggering criteria for Buneman instability and boundary conditions for existence of multiple double layers (MADL) in glow discharge plasma. The MADLs are generated by accelerating plasma electrons towards a positively biased electrode submerged in it. The boundary conditions for the formation and existence of MADL are obtained from the experiment in terms of electron drift velocity ( ν d ) and electron thermal velocity ( ν t e ). The MADL is found to exist within the range 3 ν t e ≥ ν d ≥ 1.3 ν t e . For the condition ν d ≥ 1.3 ν t e , rise of an instability and simultaneous formation of MADL is observed in the experiment. The analysis of fluctuations in floating potential showed that the instability has all the characteristics of Buneman instability.

The behavior of short-wavelength electromagnetic waves passing through a warm motional plasma is studied. The velocity and the self-magnetic field of the plasma particles are directed transversely to the direction of wave propagation. Using local approximation method, dielectric tensor and dispersion relation of perpendicular waves are derived employing the Fluid-Maxwell model. The role of temperature in propagation of EM waves, and as a result, in the instability caused by interaction between extraordinary EM waves and modified electron plasma waves is demonstrated. Moreover, the effects of self-magnetic field strength on the instability are illustrated.

A model is constructed allowing computer simulations of the near-wall area of a planar plasma sheet in conditions where the steady state of the plasma is supported by the production of charged particles in a region removed from the wall. Calculations have revealed variation in the energy distribution of the electrons in both time and spatially over the sheet width (cooling the electronic component) due to absorption of fast electrons at the walls bounding the plasma volume. It is shown that the plasma density profile across the sheet width has an abrupt decrease at the boundary of the region of plasma regulation. Thus the standard concepts of the potential and plasma density distributions in the sheath and presheath based on the assumption of a stable energy distribution for the electrons in the presheath yields inaccurate results for the plasma sheet where the ionization source is remote from the wall.

In this contribution we have presented two techniques for determination of plasma equilibrium position in IR-T1 tokamak: Relaxation and optical techniques. An analysis method of tokamak plasma equilibrium by a relaxation method with specified magnetic axis was presented. The degrees of freedom due to designated positions of the magnetic axis are possible by using poloidal field coil currents. Stable steady state tokamak plasma equilibria are calculated along with the Magnetohydrodynamic (MHD) potential energy. The plasma generates a plasma current which partially or fully cancels the magnetic field from the poloidal field coils. For low-temperature plasmas, the plasma current distribution is centrally peaked; for high-temperature plasmas, the plasma current has a hole. A centrally peaked current distribution in a low-temperature plasma is evolved into a current distribution with a hole by increasing the plasma pressure by Ohmic heating, RF heating, or by neutral beam injection heating. In the second technique, an image processing technique is used for the output signal of CCD camera. Then, plasma emission intensity profile and plasma position were obtained. Results were compared and discussed.

The “Vlasov-Maxwell system” is a groundbreaking differential procedure to visualize, model, simulate and further analyze the vigorous performance of plasma (collisionless) in the presence of the different fields (electromagnetic). In this frame of reference, the analysis of “Vlasov-Maxwell system” with the deep conceptions of (time-fractional) calculus is a novel benchmark and also the key intentions of this study. For this purpose, (1D + 1P) dimensional semi-relativistic time-fractional Vlasov-Maxwell system is formulated with the physical significances of the geometry. Furthermore, to fabricate the numerical consequences, we suggest (and also implement) an innovative algorithm which based on spectral and finite-difference estimations. The spatial and temporal variables are handled by using sifted Gegenbauer polynomials and finite-difference calculations respectively. Numerous simulations are executed to validate the reliability and accuracy of anticipated method. Error bound convergence and stability of the method is inspected numerically. Moreover, the established technique can be used conveniently to observe the numerical result of other multi-dimensional fraction (variable) order problems of physical nature.

The effects of relativistic electrons and spatial plasma nonuniformity of density on periodic absolute parametric instability (API) of electrostatic waves in a relativistic 1 − D nonuniform magnetoactive plasma are investigated in a cylindrical geometry. We use the separation method to solve the two-fluid plasma equations, which describe the system. The method used enables us to determine the frequencies and growth rates of unstable modes and the self-consistent electric field. Plasma electrons are considered to have a relativistic velocity. Increment has found in the buildup of the oscillations, and it is shown that the spatial nonuniformity of the plasma exerts a stabilizing effect on the parametric instability. It is shown that the growth rate of the API in relativistic plasma is reduced compared to nonrelativistic plasma. Independent of the geometry of the problem (plane and cylinder), the results of the API in a relativistic plasma waveguide are still valid. The proposal approach (Ȝseparation methodȝ) is significantly simpler that the method ordinarily employed in the theory of parametric resonance in nonuniform plasma. Therefore, it is of special interest to apply the separation method to solution of different problems involving parametric excitation of electrostatic waves in bounded nonuniform plasma.

In this paper, we consider THz plasma radiation in ungated cylindrical heterostructure nanowire (NW) or carbon nanotube (CNT) via perturbation approach, considering the effect of viscosity, momentum relaxation time and drift velocity as sufficiently small quantities. The scalar potential, channel charge and current are determined by solving Euler, continuity and Poisson equations in cylindrical coordinates with appropriate boundary conditions using Dyakonov-Shur plasma theory. We obtain a general dispersion relation, plasma frequency, increment and the radiated power. It is shown that in the limit of small radius, the plasma frequency behaves logarithmically while in the limit of large radius, the plasma frequency approaches to the plasma frequency of flat two-dimensional electron gas (flat-2DEG). We show that as in the flat-2DEG, drift velocity increases instability of plasma waves while viscosity and momentum relaxation time decreases the instability.

The techniques of investigation of low-frequency instabilities of the current sheet in quasi-linear approximation with due regard to the effect of plasma polarization is described. This makes it possible to study the mechanism of the reverse impact of the developing instability modes of nonelectroneutral current sheet on the background distribution function. Evolution equations of the equilibrium distribution function of the plasma current sheet and the perturbation of the electromagnetic field are derived. Algorithms for solution of evolution equations are developed. A dispersion curve for the plasma wave with damping decrement propagating along the magnetic field is derived.

We report herein experimental observation and mechanistic interpretation of the evolution and self-acceleration of constant-pressure, spherically expanding H2/O2/N2 flames, subjected to hydrodynamic and diffusional-thermal instabilities over a wide range of pressure, equivalence ratio and thermal expansion ratio. Results show the existence of three distinct stages of flame propagation affected by the development of the instability cells, namely smooth expansion, transition, and saturated states of cell development. The onset of the instabilities is primarily controlled by the diffusional-thermal instability, while characteristics of the subsequent transition to and maintenance of the saturated state is controlled by the hydrodynamic instability. The acceleration exponent for the fully developed saturated instability is found to be around 1.2–1.4, which is smaller than 1.5, the suggested value for self-turbulization.

We present a new particle-merging algorithm for the particle-in-cell method. Based on the concept of the Voronoi diagram, the algorithm partitions the phase space into smaller subsets, which consist of only particles that are in close proximity in the phase space to each other. We show the performance of our algorithm in the case of the two-stream instability and the magnetic shower., 11 figures

The influence of magnetic field and dust rotation on the resonant instability of surface electrostatic-ion-cyclotron wave is kinetically investigated in a semi-bounded warm magnetized dusty plasma. The dispersion relation and the temporal growth rate of the surface electrostatic-ion-cyclotron wave are derived by the specular-reflection boundary condition including the magnetic field and dust rotation effects. It is found that the instability domain decreases with an increase of the rotation frequency of elongated dust grain. It is also found that the dependence of the propagation wave number on the temporal growth rate is more significant for small ion cyclotron frequencies. In addition, it is shown that the scaled growth rate increases with an increase of the strength of magnetic field. The variation of the domain and magnitude of temporal growth rate due to the change of plasma parameters is also discussed.

Considering a class of solutions where the density perturbations are functions of time, but not of space, we derive a new exact large amplitude wave solution for a cold uniform electron plasma. Thi ...

Plateau-Rayleigh instability describes the infinite falling stream of fluid breaks into smaller droplets. With the development of nanotechnology, more and more attention is being drawn to Plateau-Rayleigh instability. This surface tension-driven instability performs well in the preparation of the nanoparticles, especially in photonics applications, such as optical micro-resonators in nano-biosensing systems. In this article, we mainly adopt the thermal fluid coupling method. The effect of temperature field on instability is studied with the aid of numerical simulation. In addition, the radius of the inner fluid column, the thickness of the outer fluid, and the temperature gradient are also studied to explore how the factors influence the Plateau-Rayleigh instability. The wavelength of the instability is characterized by droplet diameter, which is formed through the process caused by Plateau-Rayleigh instability.

In this paper, the mechanism of two-phase flow instability in parallel narrow channels is studied theoretically, and the characteristic of the flow instability is discussed in detail. Due to the significant confining effect of the narrow channel on the vapor–liquid interface, the two-phase flow resistance in the narrow channel is probably different from that in conventional channel. Therefore, the vapor confined number ( N conf ), defined by the size of narrow channel and bubble detachment diameter, is considered in the “Chisholm B model” to investigate the two-phase flow pressure drop. The flow instability boundaries are plotted in parameter plane with phase-change-number ( N pch ) and subcooling-number ( N sub ) under different working conditions. It is found that the predicted result agrees well with the experimental result. According to the predicted result, the oscillation behaviors near the flow instability boundary indicate that the Supercritical Hopf bifurcation appears in high sub-cooled region and the Subcritical Hopf bifurcation appears in low sub-cooled region. Also, a detailed analysis about the effects of key parameters on the characteristic of two-phase flow instability and the flow instability boundary is proposed, including the effects of inlet subcooling, heating power, void distribution parameter and drift velocity.

The acceleration of electrons by a plasma wave in the presence of density ripple in plasma has been investigated. Plasma density ripple can excite higher harmonics of different phase velocities of the fundamental plasma wave. The combined role of the different harmonics of the plasma wave contributes significantly in electrons energy gain during acceleration by the fundamental plasma wave. Our calculation shows that the plasma electrons gain considerable energy during the acceleration by the plasma waves in the presence of a density ripple in plasma. The initial electron energy and the ripple density play an important role for the acceleration of an electron.

The quantum mechanical effect on the plasma two-stream instability is studied based on the dielectric function approach. The analysis suggests that the degenerate plasma relevant to the inertial confinement fusion behaves differently from classical plasmas when the electron drift velocity is comparable to the Fermi velocity. For high wave vector comparable to the Fermi wave vector, the degenerate quantum plasma has larger regime of the two-stream instabilities than the classical plasma. A regime, where the plasma waves with the frequency larger than 1.5 times of the Langmuir wave frequency become unstable to the two-stream instabilities, is identified.

We consider a cold plasma in order to find new large-amplitude wave solutions in the long-wavelength limit. Accordingly we derive two generic coupled equations which describe the energy exchange be ...

A theoretical investigation on amplification of electrostatic ion acoustic wave in magnetically confined plasma has been presented in this paper. This investigation considers nonlinear wave–particle interaction process, called plasma maser effect, in presence of drift wave turbulence supported by magnetically confined inhomogeneous plasma. The role of associated nonlinear dissipative force in this effect in a confined plasma has been analyzed. The nonlinear force, which arises as a result of resonant interaction between electrons and modulated fields, is shown to drive the instability. Using the ion fluid equation and the ion equation of continuity, the nonlinear dispersion relation of a test ion acoustic wave has been derived, and the growth rate of ion acoustic wave in presence of low frequency drift wave turbulence has been estimated using Helimak data.

The streaming of an intense ion beam relative to background plasma can cause the development of fast electrostatic collective instabilities. The plasma waves produced by the two-stream instability modify the ion beam current neutralization and produce non-linear average forces which can lead to defocusing of the ion beam. Recently, a theoretical model describing the average de-focusing forces acting on the beam ions has been developed, and the scalings of the forces with beam-plasma parameters have been identified (Startsev et al. in press [1] ). These scalings can be used in the development of realistic ion beam compression scenarios in present and next-generation ion-beam-driven high energy density physics and heavy ion fusion experiments. In this paper the results of particle-in-cell simulations of ion beam propagation through neutralizing background plasma for NDCX-II parameters are presented. The simulation results show that the two-stream instability can play a significant role in the ion beam dynamics. The effects of velocity tilt on the development of the instability and ion beam compressibility for typical NDCX-II parameters are also simulated. It is shown that the two-stream instability may be an important factor in limiting the maximum longitudinal compression of the ion beam.

In this paper, we propose energy-conserving numerical schemes for the Vlasov-Amp\`{e}re (VA) systems. The VA system is a model used to describe the evolution of probability density function of charged particles under self consistent electric field in plasmas. It conserves many physical quantities, including the total energy which is comprised of the kinetic and electric energy. Unlike the total particle number conservation, the total energy conservation is challenging to achieve. For simulations in longer time ranges, negligence of this fact could cause unphysical results, such as plasma self heating or cooling. In this paper, we develop the first Eulerian solvers that can preserve fully discrete total energy conservation. The main components of our solvers include explicit or implicit energy-conserving temporal discretizations, an energy-conserving operator splitting for the VA equation and discontinuous Galerkin finite element methods for the spatial discretizations. We validate our schemes by rigorous derivations and benchmark numerical examples such as Landau damping, two-stream instability and bump-on-tail instability.

Compressibility effects on Rayleigh–Taylor instability in inhomogeneous plasma rotating uniformly in an external vertical magnetic field have been investigated. Using the exponential density distribution and in the presence of a fixed boundary condition, the linear growth rate is obtained for a finite compressible plasma layer. As well as the linear growth rate of a heavy compressible plasma layer supported by a lighter one is obtained. It is shown that, in the case of a finite compressible plasma layer and in the absence of an external magnetic field the system is always instable, while in the presence of an external magnetic field the system capitulates to the stability role that plays it. In the case of two compressible plasma layers, the compressibility (the ratio of specific heat values) has a stabilizing role that increases with the presence of an external vertical magnetic field. While the equilibrium pressure at the interface has an instability effect on the growth rates.

A direct energy conversion scheme to convert plasma kinetic energy into pulsed electrical energy, based on magnetic flux compression (MFC) by an inertial fusion plasma sphere, has been examined earlier. The plasma sphere, expanding across a magnetic field, is subject to the Magnetic Rayleigh–Taylor (MRT) instability. Therefore, 2D MHD simulations have been performed to analyze the MRT instability and its implications for the proposed MFC system. The simulation takes into account the effects of MFC and geometric divergence due to spherical plasma expansion. Single-mode sinusoidal perturbation evolution exhibits linear exponential growth followed by a non-linear phase towards stagnation time. We also note that near the time of stagnation, the growth in amplitude of the modes, although exponential in nature, is much lower than the growth predicted by linear theory. Furthermore, the instability amplitudes are not large enough for αin ⩽ 0.1λin to severely disturb the smooth MFC during the first expansion phase. However, the growth of modes with αin ⩾ λin causes plasma jetting, especially for longer λ modes, and can lead to significant reduction in MFC efficiency.

Parametric instability of a cylindrical thin shell with periodically time-varying rotating speeds is studied in the paper. Energy formulation based upon Love's thin shell theory and the assumed mode method is utilized to obtain the governing equations of a rotating cylindrical shell under simply supported condition. Considering the time-varying rotating speeds, the second order differential equations of the system have time-periodic gyroscopic and stiffness coefficients. The multiple scales method is utilized to obtain the boundaries of both primary and combination instabilities analytically. The primary instability occurs when the excitation frequency is near twice of the natural frequency. The excitation frequency close to the sum of two natural frequencies might lead to the occurrence of combination instability. Numerical simulations are conducted to verify the analytical results. It is shown that the primary instability regions for each mode always appear in the periodically rotating cylindrical shell. Their widths increase continually with excitation amplitude of the time-periodic rotating speed. For certain modes, the combination instability region might not exist. The conditions for its existence are obtained analytically and verified by numerical simulations. Increasing the constant rotating speed would greatly enhance the instability regions. Moreover, it might also cause the appearance of combination instability region.

A possible scheme for increasing the injection efficiency in laser plasma accelerators is proposed. It allows an improvement of both the number of captured electrons and the energy spread. The operation in linear regime is discussed. The plasma channel is divided into two stages: the modulating stage with a variable plasma density for pre-bunching the beam and the accelerating stage with a constant plasma density. The variation of the plasma density in the bunching stage and the matching between the stages are discussed.

The Rayleigh-Taylor instability is a fundamental instability of an interface between two fluids of different densities, which occurs when the light fluid is pushing the heavy fluid. During the nonlinear stages, the growth of the Rayleigh-Taylor instability is greatly affected by three-dimensional effects. To investigate three-dimensional effects on the Rayleigh-Taylor instability, we introduce a new method of computation of the flow of two incompressible and immiscible fluids and implement a time-dependent pressure boundary condition that relates to a time-dependent density field at the domain boundary. Through numerical examples, we observe the two-layer roll-up phenomenon of the heavy fluid, which does not occur in the two-dimensional case. And by studying the positions of the bubble front, spike tip, and saddle point, we show that the three-dimensional Rayleigh-Taylor instability exhibits a stronger dependence on the density ratio than on the Reynolds number. Finally, we perform a long time three-dimensional simulation resulting in an equilibrium state.

The stability of coasting ion beams against residual gas electrons accumulating in the beam potential is studied. We analyze the instability threshold intensities for ion beams of different charge state and mass using the linear centroid theory. Numerical simulations are used to study the thresholds for realistic transverse beam distributions. The effect of Coulomb collisions between beam ions and electrons is analyzed analytically and numerically using the Langevin equations. We show that at low residual gas pressures Coulomb collisions limit the neutralization degree of the ion beam to values below the instability threshold.

Recent 3D studies on plasma blobs (coherent structures found in the edge region of magnetic confinement devices) have demonstrated that the drift wave instability can strongly limit the blob’s coherency and cross field convective nature that is predicted by 2D theory. However, the dominant unstable drift wave modes that effect plasma blobs were found to exist in parameter regimes that only marginally satisfied several of the major assumptions considered for the validity of the reduced collisional fluid equations used in the study. Namely, the neglect of electron heat flow, finite electron mean free path effects, and thermal ions. A follow up study demonstrated how the drift wave instability might change if a set of equations that does not suffer from the limitations mentioned above were considered. In the present paper, the results of this later work are used to discuss the limitations on using the collisional fluid equations for 3D studies of plasma blobs.

This paper presents an investigation of the propagation of rippled laser beam in a collisionless plasma and its effect on and the excitation of electron plasma wave and particle acceleration, when relativistic and ponderomotive nonlinearities are simultaneously operative. Electron plasma wave (EPW) coupling with rippled laser beam arises on account of the relativistic change in the electron mass and the modification of the background electron density due to ponderomotive nonlinearity. When the electron plasma wave gets coupled to the rippled laser beam, a large fraction of the pump energy gets transferred to EPW and this excited EPW can accelerate the electrons. Analytical expressions for the growth rate of the laser spike in plasma, beam width of the rippled laser beam and excited electron plasma wave have been obtained using paraxial ray approximation. These coupled equations are solved analytically and numerically to study the growth of laser spike in plasma and its effect on the self focusing of rippled laser beam in plasma, amplitude of the excited electron plasma wave and particle acceleration. The result shows that the effect of including ponderomotive nonlinearity significantly affects the growth of laser spike in plasma, excitation of electron plasma wave as well as the number of energetic electrons in particle acceleration process. The results are presented for typical laser plasma parameters.

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.

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 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.

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.

A linear MHD instability of the electric current sheet, characterized by a small normal magnetic field component, varying along the sheet, is investigated. The tangential magnetic field component is modeled by a hyperbolic function, describing Harris-like variations of the field across the sheet. For this problem, which is formulated in a 3D domain, the conventional compressible ideal MHD equations are applied. By assuming Fourier harmonics along the electric current, the linearized 3D equations are reduced to 2D ones. A finite difference numerical scheme is applied to examine the time evolution of small initial perturbations of the plasma parameters. This work is an extended numerical study of the so called “double gradient instability”, – a possible candidate for the explanation of flapping oscillations in the magnetotail current sheet, which has been analyzed previously in the framework of a simplified analytical approach for an incompressible plasma. The dispersion curve is obtained for the kink-like mode of the instability. It is shown that this curve demonstrates a quantitative agreement with the previous analytical result. The development of the instability is investigated also for various enhanced values of the normal magnetic field component. It is found that the characteristic values of the growth rate of the instability shows a linear dependence on the square root of the parameter, which scales uniformly the normal component of the magnetic field in the current sheet.

The spatial structure and stability properties of the coupled Alfven and drift compressional modes in a space plasma are studied in a gyrokinetic framework in a model taking into account field-line curvature and plasma and magnetic field inhomogeneity across the magnetic shells. The perturbation is found to be localized in two transparent regions, the Alfven and drift compressional transparent regions, where the wave vector radial component squared is positive. Both regions are bounded by the resonance and cut-off surfaces, where the wave vector radial component turns into infinity and zero, respectively. An existence of the drift compressional resonance is one of the most important results of this work. It is argued that on the surface of this resonance the longitudinal and azimuthal components of the wave's magnetic field have a pole and logarithmic singularities, respectively. The instability conditions and expressions for the growth rate of the coupled modes have been obtained. In the Alfvenic transparent region, an instability occurs in the presence of the negative plasma temperature gradient. This instability does not lead to a non-stationary wave behavior: all the energy gained from the resonance particles was finally absorbed owing to any dissipation process. In a drift compressional transparent region, a necessary condition for the instability is the growth of the temperature with the radial coordinate. The growth rate is almost independent of the radial coordinate, which means that the wave energy gained from the particles cannot disappear. It will lead to an ever increasing wave amplitude, and no stationary picture for the unstable drift compressional mode is possible.

Proceedings of the 19th International Conference on Plasma-Surface Interactions in Controlled Fusion; International audience; The transition between the core and scrape-off layer of a tokamak corresponds to a marked momentum shear layer, owing to sheath acceleration on limiters which drives near-sonic flows along the plasma magnetic field in the scrape-off layer, and a parallel shear flow instability can possibly be triggered. The possibility of this instability driven by the velocity gradient is investigated numerically, using a minimum model of particle and parallel momentum transport in the edge of a tokamak, in a computational domain modelling a limiter plasma with background turbulence modelled as an effective diffusion. It is found that unstable regions can exist in the vicinity of a limiter, in agreement with experimental findings, when momentum radial transport - and therefore coupling between SOL and core flows - is sufficiently weak. Instability is reinforced by core rotation, and is found to be maximum downstream of the limiter (with respect to the core plasma flow).

Negative plasma potentials were obtained in DC hot filament unmagnetized electropositive argon plasma for sufficiently low neutral pressure. Double layers provide ion and electron confinement near the walls. The potential profiles from the center of the plasma to the potential minima are quite similar in shape to those observed when the plasma has positive plasma potentials. The primary electrons emitted from the filaments are important for charge conservation and for modification of the Bohm criteria but are not important for current balance.

We investigate the problem of linear temporal instability of the modes that satisfy the dyad resonance conditions and the associated nonlinear wave interactions in jets driven by either a constant or a variable external electric field. A mathematical model, which is developed and used for the temporally growing modes with resonance and their nonlinear wave interactions in electrically driven jet flows, leads to equations for the unknown amplitudes of such waves. These equations are solved for both water and glycerol jet cases, and the expressions for the dependent variables of the corresponding modes are determined. The results of the generated data for these dependent variables versus time indicate, in particular, that the instability resulted from the nonlinear interactions of such modes is mostly quite strong but can also lead to significant reduction in the jet radius.

Energy exchange between waves and resonant (usually energetic) particles is an essential feature of wave–particle interactions in plasma. If the resonant interaction in a magnetized unstable plasma involves two or more cyclotron resonances, the wave excitation can, at the same time, mediate the energy transfer between different populations of energetic particles. This effect, which is particularly pronounced in a marginally unstable plasma, is discussed by example of whistler–electron interactions in connection with particle energization in the Earthʼs radiation belts. The process under discussion is similar, although not identical, to alpha channeling known in the physics of tokamak plasma.

Modulation instability of an intense right-hand elliptically polarized laser beam propagating through magnetized 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 magnetized plasma by the Lorentz transformation. The Karpman equation is firstly 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 magnetized plasma is studied and the temporal growth rate of the instability is derived. The analysis shows that the peak growth rate of self-modulation instability is increased due to the axial magnetization of plasma. It is also shown that the growth rate of modulation instability is increased significantly near the critical surface in a laser–plasma.

The effect of magnetic fields in different direction, on the instability of thermocapillary convection in a rectangular cavity, with differentially heated side walls, filled with two viscous fluids, is investigated in the absence of gravity. The computational results show that, the electromagnetic damping of the hydrothermal wave instability under z-direction magnetic field is the most efficient, that of y-direction magnetic field is the second, and the magnetic field parallel to the x-direction results in the weakest damping. Furthermore, for imposing on any magnetic fields in arbitrary orientation, the hydrothermal wave instability can be fully suppressed when the magnetic field intensity is enough large.

A non-local theory is developed to study the Rayleigh–Taylor instability in an inhomogeneous dusty plasma in the presence of a uniform magnetic field. Using the fluid equations and the dynamics of charged dust grains, an eigenmode equation is derived to study the stability of the mode. Typical space parameters in the vicinity of Saturn are used to investigate the stability of the mode. The growth rate of the Rayleigh–Taylor is found to be drastically higher in a dusty plasma than in a pure plasma. This might have a wider consequence in explaining the origin of low-frequency modes in various situations in the space atmosphere. The effects of the dust charge, and the dust density on the growth rate of the instability are also studied.

We examine the drift instability of a magnetized 2D electron plasma in a weak periodic potential, taking account of a steady current. In this, we treat a strong magnetic field inducing Landau quantization, and analyze both the inter- and intra-Landau band aspects of the magneto-plasmon spectrum within the framework of the random phase approximation, determining the occurrence of magnetoplasmon instability as a function of drift speed.

The plasma instability process during internal gravity wave propagation through the ionospheric E region is considered. The growth rate of the instability has been found and it has been shown that it depends on perturbation wavelength, gravity wave parameters and direction of propagation. The conditions for the instability are favorable when the vorticity of the associated neutral motion becomes antiparallel to the geomagnetic field. In the proposed instability mechanism plasma irregularities could seed the large-scale sporadic E layer structuring because they are generated in situ as a part of the same neutral wind structure that serves to initiate the formation of the layer.

In the present work, the generation of large-scale zonal flows and magnetic field by short-scale collision-less electron skin depth order drift-Alfven turbulence in the ionosphere is investigated. The self-consistent system of two model nonlinear equations, describing the dynamics of wave structures with characteristic scales till to the skin value, is obtained. Evolution equations for the shear flows and the magnetic field is obtained by means of the averaging of model equations for the fast-high-frequency and small-scale fluctuations. It is shown that the large-scale disturbances of plasma motion and magnetic field are spontaneously generated by small-scale drift-Alfven wave turbulence through the nonlinear action of the stresses of Reynolds and Maxwell. Positive feedback in the system is achieved via modulation of the skin size drift-Alfven waves by the large-scale zonal flow and/or by the excited large-scale magnetic field. As a result, the propagation of small-scale wave packets in the ionospheric medium is accompanied by low-frequency, long-wave disturbances generated by parametric instability. Two regimes of this instability, resonance kinetic and hydrodynamic ones, are studied. The increments of the corresponding instabilities are also found. The conditions for the instability development and possibility of the generation of large-scale structures are determined. The nonlinear increment of this interaction substantially depends on the wave vector of Alfven pumping and on the characteristic scale of the generated zonal structures. This means that the instability pumps the energy of primarily small-scale Alfven waves into that of the large-scale zonal structures which is typical for an inverse turbulent cascade. The increment of energy pumping into the large-scale region noticeably depends also on the width of the pumping wave spectrum and with an increase of the width of the initial wave spectrum the instability can be suppressed. It is assumed that the investigated mechanism can refer directly to the generation of mean flow in the atmosphere of the rotating planets and the magnetized plasma.

To achieve maximum energy density, an intense ion beam must be compressed radially and longitudinally while its space-charge is neutralized by background plasma. An ion beam propagating through background plasma may be subject to the electrostatic two-stream instability and the electromagnetic Weibel instability. The electrostatic two-stream instability may lead to longitudinal bunching of the beam pulse, and eventual longitudinal beam heating. Consequently, this could degrade the longitudinal compression of the beam pulse. Similarly, the electromagnetic Weibel instability may cause transverse filamentation of the beam, which may degrade transverse compression. In this paper, we use an eikonal (Wentzel–Kramer–Brillouin, WKB) approach to analyze the space–time development of the two-stream and Weibel instabilities during transverse and longitudinal compression of an intense heavy ion beam pulse propagating through neutralizing background plasma.

This study presents several observations of the Cluster spacecraft on September 24, 2003 around 15:10 UT, which show necessary prerequisites and consequences for the formation of the so-called modified-two-stream instability (MTSI). Theoretical studies suggest that the plasma is MTSI unstable if (1) a relative drift of electrons and ions is present, which exceeds the Alfven speed, and (2) this relative drift or current is in the cross-field direction. As consequences of the formation of a MTSI one expects to observe (1) a field-aligned electron beam, (2) heating of the plasma, and (3) an enhancement in the B-wave spectrum at frequencies in the range of the lower-hybrid-frequency (LHF). In this study we use prime parameter data of the CIS and PEACE instruments onboard the Cluster spacecraft to verify the drift velocities of ions and electrons, FGM data to calculate the expected LHF and Alfven velocity, and the direction of the current. The B-wave spectrum is recorded by the STAFF instrument of Cluster. Finally, a field aligned beam of electrons is observed by 3D measurements of the IES instrument of the RAPID unit. Observations are verified using a theoretical model showing the build-up of a MTSI under the given circumstances.

Under influence of external gravity generated by Galactic all components excluding ISM, a magnetized gas disk may experience both Parker and convective instabilities. Growth rate of the convective instability increases with decreasing perturbation wavelength, and the convective motion makes sheet-like structures all over before the Parker instability forms structures of any meaningful size in the disk. Yet the Parker instability is thought to be an ideal route to form large-scale condensations in the Galaxy. In search of a means to curb convective activities in the Galactic ISM disk, the external gravity is replaced by self-gravity as a driving force of the Parker instability and the gravitational instability is invoked to reinforce the Parker instability. Perturbation of interchange mode is known to trigger convective instability in such disk and the one of undular mode to activate the Parker instability, while the gravitational instability can be triggered by both modes. Therefore, the resulting Jeans instability would help the Parker instability to overcome disrupting behavior of the convection. Dynamical properties of the disk can be characterized by ratio α of magnetic to gas pressure, adiabatic exponent γ, scale height H of the ISM, and disk thickness za. A linear stability analysis has been done to the disk, and the maximum growth rate of the Parker–Jeans instability is compared with that of the convective instability. The latter may or may not be higher than the former, depending on the disk parameters. The Parker–Jeans instability has chances to override the convective instability, when the disk is thicker than a certain value. In the disk thinner than the critical one, the Jeans instability can always suppress the convection. Since the growth rate of the convective instability is proportional to local gravitational acceleration, thereby in the general Galactic gravity, the convective instability works actively only in upper regions, we expect chaotic features to appear in regions of low density far from Galactic mid-plane.

We use a three-dimensional macro-particle code (implicit-particle simulation) to examine the evolution of a small magnetic flux rope, where “small” means that its radius is close to the kinetic length scale of protons or electrons. Small flux ropes have been observed in the dayside ionospheres of Venus and Mars. In our simulations, we assume that the initial low- β force-free flux rope is maintained by the electron current: an electron beam flows in the flux rope along the magnetic field lines. The simulation results show that electrostatic two-stream (Buneman) instability is generated around the flux rope axis where the velocity of the electron beam is higher than the electron thermal velocity or the acoustic velocity. Electrons there are heated considerably in the direction parallel to the magnetic field by the instability, and an electron hot tube is formed. The magnetic field deviates from the initial force-free field although the helical structure of the magnetic field is maintained. These results indicate that the electron hot tubes will be evidence of flux rope formation in the low- β region, i.e., in the interaction region between the solar wind and the ionosphere, if they are found by high-resolution observations in the upper ionosphere.

A kinetic model which takes into account gas jet photoionization by an ultrashort linearly polarized EUV/X-ray free electron laser (FEL) pulse, a self-generated low frequency electric field, and elastic electron scattering on atoms is introduced to study the photoionization two-stream (PITS) instability. The evolution of PITS instability is described in terms of an integral equation for electron density perturbations. This paper presents a generalization of previous theories of the PITS instability in collisionless plasmas. The instability is produced by the anisotropy of photoionized electrons and is strongly affected by electron–atom collisions. Relaxation of the PITS instability is studied for different relations between the FEL pulse duration, the instability growth time, and the electron collision time.