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In this work, we investigate the properties of ion acoustic waves generated by negative heavy ions in a multi-component non-Maxwellian electrostatic plasma, consisting of electrons, positive and negative heavy ions, and a background population of dust particles. In the absence of external energy source and collisions, the ion acoustic waves are subject to Landau damping. We perform a collisionless linear instability analysis within a slow damping approximation and study the effect of various plasma conditions on the damping rate. Our model is highly relevant to multi-ion laboratory plasmas and has been applied to K– SF6 and K– C7F14 mixtures in particular. ispartof: Physics of Plasmas vol:24 issue:9 pages:093708-093717 status: published

A relativistic quantum-hydrodynamic plasma model is proposed, to model the propagation ofelectrostatic waves in an ultradense quantum electron-ion plasma in the presence of an ion beam. Adispersion relation is derived for harmonic waves, and the stability of electrostatic wavepackets isinvestigated. Three types of waves are shown to exist, representing a modified electron plasma(Langmuir-type) mode, a low-frequency ion acoustic mode, and an ion-beam driven mode, respectively.Stability analysis reveals the occurrence of an imaginary frequency part in three regions.The dependence of the instability growth rate on the ion beam parameters (concentration andspeed) has been investigated.

The energetic electron spectra formed during magnetic reconnection between two laser-produced plasma bubbles are investigated by use of two-dimensional particle-in-cell simulations. It is found that the evolution of such interaction between the two plasma bubbles can be separated into two distinct stages: the squeezing and reconnection stages. In the squeezing stage, when the two plasma bubbles expand quickly and collide with each other, the magnetic field in the inflow region is greatly enhanced. In the second stage, a thin current sheet is formed between the two plasma bubbles, and then magnetic reconnection occurs therein. During the squeezing stage, electrons are heated in the perpendicular direction by betatron acceleration due to the enhancement of the magnetic field around the plasma bubbles. Meanwhile, non-thermal electrons are generated by the Fermi mechanism when these electrons bounce between the two plasma bubbles approaching quickly and get accelerated mainly by the convective electric field associated with the plasma bubbles. During the reconnection stage, electrons get further accelerated mainly by the reconnection electric field in the vicinity of the X line. When the expanding speed of the plasma bubbles is sufficiently large, the formed electron energy spectra have a kappa distribution, where the lower energy part satisfies a Maxwellian function and the higher energy part is a power-law distribution. Moreover, the increase of the expanding speed will result in the hardening of formed power-law spectra in both the squeezing and reconnection stages.

We have carried out the research of plural three-wave resonances of space charge wave (SCW) harmonics in the transit section of the klystron type two-stream superheterodyne free-electron laser (TSFEL) with helical electron beam in cubic non-linear approximation. We have found out that two-stream instability critical frequency increases with increasing of two-stream electron beam input angle in the focusing longitudinal magnetic field. Due to this fact, the frequency domain in which plural three-wave parametric resonances of SCW harmonics take place increases. The two-stream instability growth rate also increases in helical electron beams with increasing of the beam input angle. Therefore, the saturation lengths in TSFELs with helical electron beams are shorter compared to TSFELs utilizing straight electron beams. We have shown that SCWs with broad frequency spectrum form in two-velocity helical relativistic electron beam due to plural three-wave parametric resonances. We have demonstrated that klystron-type TSFEL with helical electron beam can be used as a source of powerful multiharmonic electromagnetic waves in millimeter-infrared wavelength ranges.

In this paper, the electromagnetic-electrostatic coupling instability excited in the two-dimensional planar-layered plasma medium with median temperature (warm motional plasma beam) is investigated by applying the initial fluctuation propagating along the planar surfaces. The dielectric tensor, obtained by the Maxwell-fluid model, is used to find the dispersion relation (DR) and different excited modes in the system. Interacting modes are investigated, in detail, by focusing on the effect of temperature on the plasma beam instability aroused by coupling the thermal excited modes (thermal-extraordinary and electron plasma modes) in the systems with various amounts of beam density. The numerical analysis of the obtained DR shows that even though the temperature effect of the plasma beam has an important role on the suppression of streaming instabilities, it does not have a considerable effect on the behavior of the coupling instability in the fluid limitation.

International audience; The role of density perturbations of the background plasma in the development of Langmuir waves generated by beam-plasma instabilities is a very debated issue in space physics. The presence of clumpy electrostatic wave-packets (in particular Langmuir waves), from in situ observations, is indeed puzzling. Several processes have been proposed to explain the formation of waveforms, such as Stochastic Growth Theory and trapping in eigenmodes. Here we explore another mechanism considering the seeding of the beam-plasma instability by density holes. We have performed several 1D-1V Vlasov simulations in the electrostatic limit. We show that in the presence of a density hole, a large amplitude solitary wave-packet of Langmuir waves is formed and that it evolves towards clumpier waveforms. Moreover, the large-amplitude wave-packets generated near the hole can reach saturation and accelerate the electrons of the beam: their velocity distribution is strongly distorted, leading to a multi-peaked structure that generates new unstable modes having phase velocities both larger and smaller than the average speed of the beam. The relationship between the wave amplitude and the characteristics of the density hole is also described, showing how the electron beam may select specific holes to generate enhanced localised Langmuir wave-packets.

Propagation of charged particle beams in background plasma as a method of space charge neutralization has been shown to achieve high degrees of charge and current neutralization and therefore can enable nearly ballistic propagation and focusing of charged particle beams. Correspondingly, use of plasmas for propagation of charged particle beams has important applications for transport and focusing of intense particle beams in electric propulsion, inertial fusion and high energy density laboratory plasma physics. However, the streaming of beam ions through a background plasma can lead to development of the two-stream instability between the beam ions and the plasma electrons [1, 2]. The electric and magnetic self-fields enhanced by the two-stream instability can lead to defocusing of the ion beam and fast scattering of an electron beam. Using particle-in-cell (PIC) simulations, we study the scaling of the instability-driven selfelectromagnetic fields and consequent defocusing forces with the background plasma density and beam ion mass. We identify plasma parameters where the defocusing forces can be reduced.

We study supersonic flow of rarefied weakly ionized plasma at diverging magnetic field. While the flows of ions and neutral are treated by particle-based direct simulation Monte Carlo method, the electron is treated as a fluid, i.e., we carried out hybrid simulation. We calculate number density, velocity, temperature, and electric potential of charged particles and neutrals when the arc plasma flows out of the uniform magnetic field into lower pressure region in a steady state. We find the velocity increase just after passing the open magnetic field line, followed by deceleration due to collisions with residual molecules. We also find the temperature increase during the deceleration. In this acceleration/deceleration phenomena, the velocity difference between the neutrals and charged species are found, which also changes the electric potential. We discuss the mechanisms of potential formation along the plasma flow mainly by the pressure difference and the friction force between the charged particles and neutral species. The numerical results are, at least qualitatively, consistent with our previous experimental results.

Conditions for the onset of Alfven ion-cyclotron instability and the spatial structure of unstable modes in an axisymmetric mirror trap with oblique injection of fast atoms are studied. It is shown that the main contribution to instability comes from the inverse population of ions in the velocity space domain into which atoms are injected. Using the distribution function of fast ions obtained by approximately solving the Fokker-Planck equation, the instability threshold in terms of β⊥ is determined in the Wentzel-Kramers-Brillouin approximation as a function of the geometric parameters and the parameters of injection and target plasma. It is demonstrated that the stability threshold increases substantially when the radius of the hot plasma decreases to a size comparable with the Larmor radius of fast ions. It is shown that the perturbed fields near the axis and at the plasma periphery can rotate in opposite directions, which is important for the interpretation of experimental data.

The evolution of the momentum distribution of particles in a nonrelativistic laser plasma is studied in the context of the kinetic theory of plasma based on the construction of propagators for the plasma particle distribution functions. Damping of plasma waves and induced braking absorption accelerate particles in a plasma. Quantum indeterminacy in energy, which is associated with the interaction of particles with plasma waves and their collisions with one another, also affects their momentum distribution. In the semiclassical approximation, general analytic expressions are obtained for the momentum distribution functions.

Propagation of optical signals measured along the atmospheric plasma-jet column according to the operational voltage polarity is analyzed with the electrostatic plasma-diffusion wave in terms of the characteristic speeds of plasma fluids, such as the plasma drift u d , the gas flow u b , and the plasma diffusion u n . For the positive voltage, the ion wave propagates with the wave-packet velocity of u g ~ c s 2 /u n , where c s is the acoustic velocity along the whole column of plasma jet without any restrictions. The electron wave propagates backward with the group velocity of electron drift with u g ~ -u ed toward the high voltage electrode right after passing of the frontline of ion wave-packet. For the negative voltage, the ion wave propagates on the high ionization column with the wave-packet velocity of u g ~ c s 2 /u n . The electron wave propagates forward while its propagation mode varies from the group velocity of u g ~ c s 2 /u n on a region of high electric field to the velocity of electron drift with ug ~ +u ed on a low field region.

The magnetic field in the plasma jet propagating from the plasma pinch region along the axis of the chamber in a megajoule PF-3 plasma focus facility is studied. The dynamics of plasma with a trapped magnetic flow is analyzed. The spatial sizes of the plasma jet region in which the magnetic field concentrates are determined in the radial and axial directions. The magnetic field configuration in the plasma jet is investigated: the radial distribution of the azimuthal component of the magnetic field inside the jet is determined. It is shown that the magnetic induction vector at a given point in space can change its direction during the plasma flight. Conclusions regarding the symmetry of the plasma flow propagation relative to the chamber axis are drawn.

Vortices observed in ionized clouds of thunderstorm fronts have the nature of plasma vortices. In this work, the need to account for the electrostatic instability of plasma in the origination, intensification, and decay of plasma vortices in the atmosphere is shown. Moisture condensation results in mass-energy transfer under the inhomogeneous spatial distribution of aerosols. If a phase volume of natural oscillations is transformed in the frequency-wave vector space in inhomogeneous plasma, the damping of plasma oscillations promotes an increase in the pressure gradients normal to the geomagnetic field. Excitation of the gradient instabilities is probable in atmospheric plasma formations.

Is shown that in the nonmagnetized plasma, besides longitudinal Langmuir resonance can exist the transverse plasma resonance. The resonance indicated can exist in the confined plasma. It is known that with the nuclear explosions the electromagnetic radiation in the very wide frequency band is observed, up to the radio- frequency range. And if the emission in field of light range can be explained by the emission of separate atoms, then emission in the region of radio-frequency band can be caused only by collective processes, which occur in the confined plasma. The use of transverse resonance makes it possible to create resonators and band-pass filters, and also lasers on the collective plasma oscillations. Transverse plasma resonance can be used also for the warming-up of plasma and its diagnostics. Is introduced the concept of magnetoelectrokinetic waves.

By employing the anisotropic plasma distribution function, the stability of circularly polarized electromag- netic (EM) waves is studied in a relativistically hot electron- positron-ion (e-p-i) plasma, investigating two specific sce- narios. First, linear dispersion relations associated with the transverse EM waves are analyzed in different possible fre- quency regimes. The expression of the aperiodic hydrody- namic instability is obtained and numerically the transverse EM modes are shown to grow exponentially. Secondly, we have found that the transverse electromagnetic wave inter- act with a collisionless anisotropic e-p-i plasma and damp through the nonlinear Landau damping phenomena. Taking the effects of the latter into consideration, a kinetic nonlin- ear Schrodinger equation is derived with local and nonlo- cal nonlinearities, computing the damping rates. The present work should be helpful to understand the linear and non- linear properties of the intense EM waves in hot relativisti

To evaluate whether interchange motion can provide the transport for the formation of the cold-dense plasma sheet in the near-Earth region, we present an event of cold-dense plasma sheet observed by five THEMIS probes after the interplanetary magnetic field turned northward, as well as their comparisons with the simulation results from the Rice Convection Model (RCM) combined with a modified Dungey force-balanced magnetic field solver. The observations of cold-dense plasma at different locations show quite different characteristics: (1) closer to the flank, the appearance is more periodic and exhibits larger fluctuations in plasma moments and magnetic field; (2) further away from the flank, the cold plasma appears later; (3) in the mixture with the cold plasma, the decrease in high-energy particle fluxes becomes less significant further away from the flank; (4) there is energy-dispersion in the cold particles at some locations; and (5) near the magnetopause, the fluctuations have the characteristics of the Kelvin-Helmholtz (K-H) vortices and the colder-denser plasma is likely to have lower entropy. In the RCM simulations, lower entropy plasma consisting of colder-denser ions and electrons was periodically released locally at the outer boundary to represent the plasma created within a K-H vortex. This lower entropy perturbation is interchange unstable and the resulting interchange motion through the magnetosphere-ionosphere coupling pushes the colder-denser plasma radially inward. The simulated particle energy spectrums at different locations qualitatively reproduce the observations, strongly suggesting that the seemingly different characteristics of cold-dense plasma observed by different probes are all a result of the same interchange-related transport mechanism.

A theoretical investigation has been carried out on the growth rate of instability of the low-frequency electrostatic waves in a partially ionized four-component magnetodustyplasma in the presence of polarization force. Utilizing the method of linear mode analysis, the results of investigation have been presented. The findings of the investigation reveal that the polarization force, the external magnetic field and the dust temperature have a tendency to destabilize the the system by increasing the growth rate of instability. On the other hand, the positive dust mass causes the instability growth rate to decrease, thereby stabilizing the system.

Kelvin–Helmholtz instability plays a particularly important role in plasma transport at magnetospheric boundaries because it can control the development of a turbulent boundary layer, which governs the transport of mass, momentum, and energy across the boundary. Waves generated at the interface can also couple into body modes in the plasma sheet and inner magnetosphere where they can play an important role in plasma sheet transport and particle energization in the inner magnetosphere. Kinetic and electron-scale effects are important for the development of K–H instability, leading to secondary instabilities and plasma mixing. The development of vortices that entwine magnetosheath field lines with magnetospheric field lines also allows reconnection and the interchange of plasma blobs from open to closed field lines. Dawn-dusk asymmetries in Kelvin–Helmholtz development at planetary boundary layers may result from several effects including plasma corotation, kinetic effects, magnetic geometry, or asymmetric distribution of plasma. Examples are provided throughout the solar system illustrating the pervasive effects of the Kelvin–Helmholtz instability on plasma transport.

It is shown that the electric field may cause instability of low-frequency potential oscillations with a period of about 1 min in the D region of the ionosphere. This is related to the fact that the attachment rate of electrons to molecules is a nonmonotonic function of the temperature: it increases at low temperatures and decreases at high temperatures. The temperature corresponding to the maximum attachment rate is about 1000 K. The development of instability can result in the formation of quasi-steady layers of the electron density with a characteristic spatial period of several tens of meters. Such inhomogeneities can affect the propagation of radio waves with wavelengths on the order of or shorter than 10 m.

Amplification of plasma oscillations in a homogeneous plasma by reducing its concentration is considered. The frequency of plasma oscillations decreases upon a decrease in the plasma concentration, and the resonant velocity of the plasma electrons, which is equal to the wave phase velocity, also decreases. Due to this, the number of resonant electrons exponentially increases in the equilibrium plasma. Since the energy of plasma oscillations is mainly determined by the contribution of the resonant electrons, this energy also increases exponentially.

The Kelvin-Helmholtz (KH) instability is studied in a two dimensional strongly coupled dusty plasma medium using a fluid approach as well as through a molecular dynamic (MD) simulation. For the fluid description the generalized hydrodynamic (GH) model which treats the strongly coupled dusty plasma as a visco-elastic fluid is adopted. For the MD studies the ensemble of particles are assumed to interact through a Yukawa potential. Both the approaches predict a stabilization of the KH growth rate with an increase in the strong coupling parameter. The present study also delineates the temporal evolution and the interaction of transverse shear waves with the collective dynamics of the dusty plasma medium within the framework of both these approaches.

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.

A fluid description is used to study the properties of two-stream instability due to interaction of a non-relativistic electron beam with quantum magnetized plasma and transverse wiggler magnetic field. It is assumed that the background plasma provides charge and current neutralization of the electron beam. The dispersion relation is obtained by solving and linearizing fluid-Maxwell equations. The resulting dispersion equation is analyzed numerically over a wide range of system parameters. The results of quantum and classical treatments are compared numerically, with including the effects of wiggler on the dispersion relation. It is found that the transverse wiggler magnetic field can strongly improve the instability of quantum plasma as well as classical plasma.

In this contribution, we have presented two techniques for the determination of plasma equilibrium position in IR-T1 tokamak: relaxation and optical methods. An analysis method of tokamak plasma equilibrium by a relaxation method with a specified magnetic axis is 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 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, radio frequency heating, or by neutral beam injection heating. In the se...

We have performed extensive one dimensional particle-in-cell (PIC) simulations to explore generation of electrostatic waves driven by two-stream instability (TSI) that arises due to the interaction between two symmetric counterstreaming electron beams. The electron beams are considered to be cold, collisionless and magnetic-field-free in the presence of neutralizing background of static ions. Here, electrons are described by the non-extensive q-distributions of the Tsallis statistics. Results shows that the electron holes structures are different for various q values such that: (i) for q > 1 cavitation of electron holes are more visible and the excited waves were more strong (ii) for q q = 0.5 the holes are not distinguishable. Furthermore, time development of the velocity root-mean-square (VRMS) of electrons for different q-values demonstrate that the maximum energy conversion is increased upon increasing the non-extensivity parameter q up to the values q > 1. The normalized total energy history for a arbitrary entropic index q = 1.5, approves the energy conserving in our PIC simulation.

The convective amplification of filamentation instability (FI) of electromagnetic waves traveling along the density ramp of a magnetized plasma is investigated. The generalized amplification factor of the instability in the presence of a DC–magnetic field is derived by obtaining the governing equations of the instability and using the slow-coupling technique to obtain an analytical expression for the amplification factor in weakly magnetized plasma. The result shows enhancement of the convective FI gain by the magnetic field, where the enhancement is stronger for lower equilibrium plasma density values.

The effect of plasma wavebreaking has been proposed to obtain single-pulse output for backward Raman amplification in plasma. However, some experiments indicate that the scheme may not be effective. In this paper, we propose the effect of Landau damping for this purpose. According to the theoretical analysis, the single pulse is generated by setting a proper plasma temperature to fully Landau damp the secondary spikes. Although the main pulse will also be partly suppressed by the damping, the effective efficiency can be enhanced. Moreover, the scheme is numerically demonstrated feasible by using the parameters of Princeton experiment [1] , [2] . Additionally, the temperature to produce single-pulse output can keep below the critical temperature at various ratios of the plasma frequency to the pump pulse frequency.

Magnetorotational instability of a weakly ionized accretion disk with an admixture of charged dust grains in a magnetic field with the axial and toroidal components is analyzed. The dispersion relation for perturbations perpendicular to the disk plane is derived with allowance for both the Hall current and the finite transverse plasma conductivity. It is shown that dust grains play an important role in the disk magnetic dynamics. Due to the effect of dust grains, the Hall current can reverse its direction as compared to the case of electron-ion plasma. As a result, the instability threshold shifts toward the short-wavelength range. Under certain conditions, electromagnetic fluctuations of any length can become unstable. It is established that the instability criterion for waves of any scale length is satisfied within a finite interval of the density ratio between the dust and electron plasma components. The width of this interval and the instability growth rate as functions of the plasma parameters and the configuration of the magnetic field in the disk are analyzed.

The growth rate of aperiodic instability of transverse and longitudinal-transverse electromagnetic field perturbations in plasma with an anisotropic bi-Maxwellian electron velocity distribution is studied. The boundaries of the instability domains in wave vector space are found, and the growth rates of field perturbations with configurations different from that corresponding to the maximum growth rate are determined.

The stability of a dusty plasma of low pressure non-self-sustained discharge is studied. It is shown that aperiodic recombination instability can be developed in plasma in a wide wavenumber range. The physical mechanism of instability is discussed. The dependence of conditions of instability development and its increment on discharge parameters is analyzed.

Laminar separation bubbles generated on a flat plate by an adverse pressure gradient are investigated using direct numerical simulations (DNSs). Two-dimensional periodic forcing is applied at a blowing/suction slot upstream of separation. Control of separation through forcing with various frequencies and amplitudes is examined. For the investigation of absolute instability mechanisms, baseflows provided by two-dimensional Navier–Stokes calculations are analysed by introducing pulse disturbances and computing the three-dimensional flow response using DNS. The primary instability of the time-averaged flow is investigated with a local linear stability analysis. Employing a steady flow solution as baseflow, the nonlinear and non-parallel effects on the self-sustained disturbance development are illustrated, and a feedback mechanism facilitated by the upstream flow deformation is identified. Secondary instability is investigated locally using spatially periodic baseflows. The flow response to pulsed forcing indicates the existence of an absolute secondary instability mechanism, and the results indicate that this mechanism is dependent on the periodic forcing. Results from three-dimensional DNS provide insight into the global instability mechanisms of separation bubbles and complement the local analysis. A forcing strategy was devised that suppresses the temporal growth of three-dimensional disturbances, and as a consequence, breakdown to turbulence does not occur. Even for a separation bubble that has transitioned to turbulence, the flow relaminarizes when applying two-dimensional periodic forcing with proper frequencies and amplitudes.

A detailed theoretical analysis is carried out of the hose instability of relativistically strong laser pulses propagating in a plasma, whose duration is less than the period of a plasma wake wave. An analytic expression is obtained for the displacement of the mass center of a wave pulse, and the effect of this instability on the modification of the spectrum of laser radiation is analyzed for a wide range of initial parameters. It is shown that the development of instability is characterized by a power-law (rather than exponential) time dependence along the propagation path and does not deteriorate the self-compression of laser pulses.

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 ...

Analysis related to the onset and evolution of the electron two-stream instability (ETSI) near a surface with a continuous photoemission flux is presented. With the help of a particle-in-cell simulation code, it is shown that when a surface emits photoelectrons due to exposure to ultraviolet photons (or due to similar mechanisms), it may lead to the onset of the ETSI due to the relative bulk velocity difference between the photoelectrons and the plasma electrons. It is shown that the ETSI thus developed is sustained through the lifetime of the plasma and prevents thermalization of the electrons, which leads to a distortion in the electron velocity distribution function (EVDF) resulting a high energy tail, at least near the surface. We have shown that the resultant EVDF can be highly Lorentzian with a spectral index of ∼1.5. The simulation results are supported with the corresponding theory, which are found to be in good agreement.

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 Jeans instability of infinite homogeneous plasma has been investigated in the presence of magnetic field considering the effect of radiative heat -loss function and quantum correction.In the presentapproach, it is initiated that the criterion of Jeans instability is modified due to radiative heat -loss function and quantumeffectin the longitudinal mode of propagation, while in transverse mode, it is affected by the presence of magnetic field. The

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.

Using the 16-moment equations that take into account heat fluxes in anisotropic collisionless plasma, the properties of magnetohydrodynamic (MHD) instabilities are investigated. For all instabilities occurring in the MHD approach (the normal incompressible firehose instability, the second compressible almost longitudinal firehose instability, and the almost transverse mirror instability of slow magnetosonic modes, as well as thermal instability caused by the heat flux directed along the magnetic field), their kinetic analogs are considered. The kinetic dispersion relation in the low-frequency range in the vicinity of the ion thermal velocity is analyzed. The flow of plasma ions along the magnetic field is taken into account. The thresholds and instability growth rates obtained in the MHD and kinetic approaches are found to be in good agreement. This indicates that the 16-moment MHD equations adequately describe the dynamics of collisionless plasma.

The quadratic nonlinear theory of multiharmonic interactions of space charge wave harmonics which increasing owing to the effect of two-stream instability in a two-stream relativistic electron beam is constructed. The multiple three-wave parametric resonance interactions take into consideration. The analysis of the influence of two-stream relativistic beam parameters on the frequency spectrum form of growing multiharmonic space charge wave excited in the investigated system is carried out

The excitation of drift waves by an electron current parallel to the magnetic field is investigated in a nonuniform plasma composed of electrons, positive ions, negative ions, and massive, negatively charged dust. Electrostatic drift waves with frequencies smaller than the ion gyrofrequencies and wavelengths larger than the ion gyroradii are considered. Linear kinetic theory is used, and collisions of charged particles with neutrals are taken into account. The present results may be relevant to laboratory collisional magnetoplasmas containing negative ions and dust.

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.

A self-consistent model of radio-frequency (RF) plasma generation in stellarators in the ion cyclotron frequency range is described. The model includes equations for the particle and energy balance and boundary conditions for Maxwell’s equations. The equation of charged particle balance takes into account the influx of particles due to ionization and their loss via diffusion and convection. The equation of electron energy balance takes into account the RF heating power source, as well as energy losses due to the excitation and electron-impact ionization of gas atoms, energy exchange via Coulomb collisions, and plasma heat conduction. The deposited RF power is calculated by solving the boundary problem for Maxwell’s equations. When describing the dissipation of the energy of the RF field, collisional absorption and Landau damping are taken into account. At each time step, Maxwell’s equations are solved for the current profiles of the plasma density and plasma temperature. The calculations are performed for a cylindrical plasma. The plasma is assumed to be axisymmetric and homogeneous along the plasma column. The system of balance equations is solved using the Crank-Nicholson scheme. Maxwell’s equations are solved in a one-dimensional approximation by using the Fourier transformation along the azimuthal and longitudinal coordinates. Results of simulations of RF plasma generation in the Uragan-2M stellarator by using a frame antenna operating at frequencies lower than the ion cyclotron frequency are presented. The calculations show that the slow wave generated by the antenna is efficiently absorbed at the periphery of the plasma column, due to which only a small fraction of the input power reaches the confinement region. As a result, the temperature on the axis of the plasma column remains low, whereas at the periphery it is substantially higher. This leads to strong absorption of the RF field at the periphery via the Landau mechanism.

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.

[1] In this paper, we study the foreshock turbulence evolution in high β region via both Cluster observation on 29 March 2002 and 1-D hybrid simulation. The quasi-sinusoidal and the irregular wave trains are both detected in this event. The former one is believed to be generated by ion-ion right-hand nonresonant instability due to the right-hand polarization and antisunward propagation in the plasma frame. Since the ion distribution associated with the wave train is more “intermediate” rather than “diffused”, we suggest that the wave train reported in this paper can be viewed as a “midstep” of “isolated” and “irregular”. From the quasi-sinusoidal to the irregular waveform, the corresponding polarizations appear to transit: right-hand wave of higher frequency (wave number) is substituted by a left-hand wave with lower frequency (wave number) in spacecraft frame. Then the 1-D hybrid simulation is applied for two cases with various velocities to study such polarization transition. By comparing observation results with the simulation, such polarization transition and “inversed cascade” (wave energy transferring from large wave number to small wave number) can be understood as the consequence of decay instability. Although decay instability cannot be initiated in high beta (β > 1) plasma in magnetohydrodynamic theory, such β dependence can be modified by ion kinetic effect. Moreover, it is found that in simulation no matter which right-hand instability is dominant in early stage, left-hand wave will be the prime component of magnetic field disturbance in the final stage.

The effect of two negative ions on the Landau damping and stellar solar wind driven instability is analyzed using kinetic theory for the Lorentzian plasmas. It is investigated that the dispersion relations, damping rates and instability growths are appreciably modified in the presence of Generalized Lorentzian or kappa distributed function and additional negative ion in our plasma system. A quantitative measurement of the threshold value of the streaming velocity is also determined to estimate the condition of the growing instability.

Conditions for the propagation of a slow extraordinary wave in dense magnetized plasma are found. A solution to the set of relativistic hydrodynamic equations and Maxwell’s equations under the plasma resonance conditions, when the phase velocity of the nonlinear wave is equal to the speed of light, is obtained. The deviation of the wave frequency from the resonance frequency is accompanied by nonlinear longitudinal-transverse oscillations. It is shown that, in this case, the solution to the set of self-consistent equations obtained by averaging the initial equations over the period of high-frequency oscillations has the form of an envelope soliton. The possibility of excitation of a nonlinear wave in plasma by an external electromagnetic pulse is confirmed by numerical simulations.