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In this paper, we have studied the influence of magnetic quantization of orbital motion of the electrons on the profile of linear and nonlinear ion-acoustic waves, which are propagating in the ultra-relativistic dense magneto quantum plasmas. We have employed both Thomas Fermi and Quantum Magneto Hydrodynamic models (along with the Poisson equation) of quantum plasmas. To investigate the large amplitude nonlinear structure of the acoustic wave, Sagdeev-Pseudo-Potential approach has been adopted. The numerical analysis of the linear dispersion relation and the nonlinear acoustic waves has been presented by drawing their graphs that highlight the effects of plasma parameters on these waves in both the linear and the nonlinear regimes. It has been noticed that only supersonic ion acoustic solitary waves can be excited in the above mentioned quantum plasma even when the value of the critical Mach number is less than unity. Both width and depth of Sagdeev potential reduces on increasing the magnetic quantization parameter η. Whereas the amplitude of the ion acoustic soliton reduces on increasing η, its width appears to be directly proportional to η. The present work would be helpful to understand the excitation of nonlinear ion-acoustic waves in the dense astrophysical environments such as magnetars and in intense-laser plasma interactions. [ABSTRACT FROM AUTHOR]

Proton-driven plasma wakefield acceleration has been demonstrated in simulations to be capable of accelerating particles to the energy frontier in a single stage, but its potential is hindered by the fact that currently available proton bunches are orders of magnitude longer than the plasma wavelength. Fortunately, proton micro-bunching allows driving plasma waves resonantly. In this paper, we propose using a hollow plasma channel for multiple proton bunch driven plasma wakefield acceleration and demonstrate that it enables the operation in the nonlinear regime and resonant excitation of strong plasma waves. This new regime also involves beneficial features of hollow channels for the accelerated beam (such as emittance preservation and a uniform accelerating field) and long buckets of stable deceleration for the drive beam. The regime is attained at a proper ratio between plasma skin depth, driver radius, hollow channel radius, and micro-bunch period. [ABSTRACT FROM AUTHOR]

For linear Langmuir waves, it is well known that the energy exchanges generally lead to a continuous dissipation, on average, from the electric form to the kinetic one. Many papers have estimated these exchanges and indeed shown that the classical Landau value γL, characterizing the electric field damping, can be derived from this estimation. The paper comes back to this demonstration and its implicit assumption of “forgetting the initial conditions.” The limits of the usual energy calculations have become much apparent recently when non-Landau solutions, decreasing with damping rates smaller than γL, have been evidenced [Belmont et al., Phys. Plasmas 15, 052310 (2008)]. Taking advantage of the explicit form provided in this paper for the perturbed distribution function, the dissipation process is revisited here in a more general way. It is shown that the energy calculations, when complete (i.e., when the role of the initial conditions is not excluded by the very hypotheses of the calculations), are indeed in full agreement with the existence of non-Landau solutions; Landau damping, by the way, appears as a particular mode of dissipation, in which the ballistic transport of the initial plasma perturbation leads to negligible effects. Two approaches are presented for this demonstration, Eulerian and Lagrangian, the first one starting from the Vlasov equation and the second from the dynamics of the individual particles. The specific role of the so-called resonant particles is investigated in both formalisms, which provides complementary pictures of the microphysics involved in the energy transfers between field and particles for Landau as well as for non-Landau solutions. [ABSTRACT FROM AUTHOR]

In a recent series of papers, the present authors developed a kinetic theory for low-frequency turbulence propagating parallel to the ambient magnetic field. Making use of this theory, it was shown that low-frequency Alfvénic turbulence may cascade to ion-cyclotron frequency range and beyond by nonlinear three-wave decay processes. The significance of such a finding is that it may lead to the proton heating by cyclotron resonance. However, the actual proton heating process was not demonstrated. The present paper complements the previous works by including the proton heating in the discussion. It is found that the left-hand circularly polarized Alfvén-cyclotron turbulence leads to a moderate heating of the protons in the perpendicular direction and cooling in the parallel direction. It is also found that ion-acoustic turbulence is generated by the decay instability process. Finally, the heating rate is shown to increase in inverse proportion to the time scale of the wave source. [ABSTRACT FROM AUTHOR]

In a recent paper by Kuhn et al. [Phys. Plasmas 13, 013503 (2006)], it has been demonstrated that in a plasma, the polytropic coefficient γ is a spatially varying quantity rather than a global constant as usually assumed in fluid theory. Assuming cold ion sources and using the asymptotic two-scale approximation (in which the ratio of the Debye length over the characteristic presheath length, [variant_greek_epsilon], is set to zero), it was found that the γ profile exhibits a sharp peak (with values roughly between 6 and 8) at the plasma-sheath boundary. In the present paper, it is shown that in a finite [variant_greek_epsilon] approach, this sharp peak is smoothed to a regular maximum, which for increasing [variant_greek_epsilon] (e.g., decreasing plasma density) decreases and finally disappears. In any case, assumptions like γ=1 and/or γ=3, which are customarily encountered in the context of fluid approaches, are disproved. Although the present results were obtained for collisionless plasmas, it is reasonable to assume that the behavior uncovered holds qualitatively for any plasma with cold ion sources. In addition to calculating time-independent theoretical solutions by means of an analytic-numerical approach, we primarily employ particle-in-cell (PIC) computer simulations, which intrinsically represent a time-dependent approach. It is confirmed that, although extreme care is required to separate physical from numerical effects, the PIC simulation method is a highly suitable tool also for future investigations of more demanding physical scenarios assuming, e.g., warm ion sources and other more complex aspects that cannot be treated realistically by analytic-numerical means alone. In addition, the extension from time-independent analytic-numerical calculation to time-dependent simulation permits us also to investigate the effect of collective plasma oscillations on the ion velocity distribution function (VDF). Although the ion VDFs obtained in our PIC simulations visibly differ in some details from the time-independent theoretical ones, the related ion-temperature and γ profiles turn out to fit their theoretical counterparts very well over significant parameter ranges. Hence, the two methods may to some extent be applied as alternative ones in future investigations on the plasma-sheath transition. [ABSTRACT FROM AUTHOR]

Recently, magnetic fields of 0.7(±0.1) gigaGauss (GG) have been observed in the laboratory in laser plasma interactions. From scaling arguments, it appears that a few gigaGauss magnetic fields may be within reach of existing petawatt lasers. In this paper, the equations of state (EOS) are calculated in the presence of these very large magnetic fields. The appropriate domain for electron degeneracy and for Landau quantization is calculated for the density-temperature domain relevant to laser plasma interactions. The conditions for a strong Landau quantization, for a magnetic field in the domain of 1–10 GG, are obtained. The role of this paper is to formulate the EOS in terms of those that can potentially be realized in laboratory plasmas. By doing so, it is intended to alert the experimental laser-plasma physics community to the potential of realizing Landau quantization in the laboratory for the first time since the theory was first formulated. [ABSTRACT FROM AUTHOR]

The nonlinear processes governing the resonant interaction of a packet of lower hybrid waves with a radially bounded electron beam spiraling in a magnetized plasma are investigated. In particular, the paper tries to answer the fundamental following questions: What are the causes of the beam bunching and the main agents of the beam self-organization occurring during the nonlinear waveparticle evolution? What is the influence of the wave packet on the stability of the formed bunches? This paper shows that, owing to the presence of wave energy dissipation out of the bounded beam volume, a competition takes place between the beam relaxation and the particle bunching processes, leading to the structuring of the beam over long distances from the injection point. In particular, two main mechanisms govern the behavior of the particles in resonance with the waves: First, the process of particle bunching which gives rise to dynamically stable and long living bunches of particles which keep resonance and strong correlations with several waves of the packet while continuously decelerated (Cherenkov resonance is considered) in the frame moving with the initial parallel beam velocity and, second, a process of particle diffusion in the velocity space concerning particles which do not experience trapping by waves or which leave a bunch through the action of large stochastic oscillations. This diffusion process cannot be well described in the frame of the weak turbulence theory, as it is noticeably perturbed by the presence of a large number of small unstable bunches which appear, merge together and disappear during the system's evolution. [ABSTRACT FROM AUTHOR]

The comment questions the formulation of the κ velocity distribution function used in our paper as compared to a slightly different form used by the authors. The difference in the distribution function necessarily leads to different number densities, thermal pressures, etc. We show that the restriction with their distribution function is that the macroscopic temperature (or average kinetic energy) is the same for all spatially uniform systems with a family of κ distributions including the Maxwellian case. The distribution function used in our paper and widely adopted in various studies of nonthermal systems, however, does not impose such a constraint; in particular, the temperature has κ dependence reflecting the kinetic nature of different statistical systems. The points made in the comment are trivial and misleading. [ABSTRACT FROM AUTHOR]

In this paper, we consider an unmagnetized plasma consisting of warm adiabatic ions, superthermal electrons, and thermal positrons. Nonlinear cylindrical and spherical modified Korteweg-de Vries (KdV) equations are derived for ion acoustic waves by using reductive perturbation technique. It is observed that an increasing positron concentration decreases the amplitude of the waves. Furthermore, the effects of the superthermal parameter (k) on the ion acoustic waves are found. [ABSTRACT FROM AUTHOR]

This paper addresses the formation of nongyrotropic current sheets resulting from slow external driving. The medium is a collisionless plasma with one spatial dimension and a three-dimensional velocity space. The study is based on particle simulation and an analytical approach. Earlier results that apply to compression of an initial Harris sheet are generalized in several ways. In a first step a general sufficient criterion for the presence of extra ion and electron currents due to nongyrotropic plasma conditions is derived. Then cases with antisymmetric magnetic and electric fields are considered. After establishing consistency of the criterion with the earlier case, the usefulness of this concept is illustrated in detail by two further particle simulations. The results indicate that the formation of nongyrotropic current sheets is a ubiquitous phenomenon for plasmas with antisymmetric fields that have evolved slowly from initial gyrotropic states. A fourth case concerns a plasma with a unidirectional magnetic field. Consistent with the general criterion, the observed final state is fluidlike in that it is approximately gyrotropic. Momentum balance is shown to include a contribution that results from accumulation of an off-diagonal pressure tensor component during the evolution. Heat flux also plays an important role. [ABSTRACT FROM AUTHOR]

Resonance zones in the Earth’s dipole magnetosphere are determined for electron cyclotron resonance with obliquely propagating very-low-frequency chorus, extremely-low-frequency hiss, electromagnetic ion cyclotron, and magnetosonic waves. The resonance zones, which are presented in (L,λ) space, where L is magnetic shell and λ is magnetic latitude, depend on the assumed particle density distributions inside and outside the plasmasphere, the specified wave bands, and the electron kinetic energy. This work is a companion paper of Ni and Summers [Phys. Plasmas 17, 042902 (2010)], which considers strictly field-aligned wave propagation. Inclusion of the wave normal angle parameter adds an extra degree of freedom to the calculations, and emphasizes the need for global observational data on the wave spectral properties. Comparison of resonance zones with global wave distributions is a useful aid in the modeling of radiation belt electron dynamics. Resonance zones are also of potential use in the interpretation of observational data on particles and waves at given points in space. [ABSTRACT FROM AUTHOR]

Wave-particle interactions are a key influence on radiation belt particle dynamics. Here electron cyclotron resonance with very-low-frequency chorus, extremely-low-frequency hiss, and electromagnetic ion cyclotron waves in the Earth’s dipole magnetosphere is analyzed. In this first of two companion papers, it is assumed that wave propagation is field aligned. The aim of this investigation is to carry out a detailed examination of “resonance zones” in (L,λ) space (where L denotes magnetic shell and λ the magnetic latitude). These zones are regions in which electron cyclotron resonance occurs for a given wave mode and waveband. Identification of resonance zones is a useful aid in the construction of realistic models of radiation belt electron dynamics, and is hence also useful in the interpretation of observational data. [ABSTRACT FROM AUTHOR]

Reconnections of magnetic fields over the solar surface are expected to generate abundant magnetohydrodynamic (MHD) discontinuities and shocks, including slow shocks and rotational discontinuities. However, the generation of fast shocks by magnetic reconnection process is relatively not well studied. In this paper, magnetic reconnection in a current sheet is studied based on two-dimensional resistive MHD numerical simulations. Magnetic reconnections in the current sheet lead to the formation of plasma jets and plasma bulges. It is further found that the plasma bulges, the leading part of plasma jets, in turn lead to the generation of fast shocks on flanks of the bulges. The simulation results show that during the magnetic reconnection process, the plasma forms a series of structures: plasma jets, plasma bulges, and fast shocks. As time increases, the bulges spread out along the current sheet (±z direction) and the fast shocks move just ahead of the bulges. The effects of initial parameters ρs/ρm, β∞, and trec on the fast shock generation are also examined, where ρs/ρm is the ratio of plasma densities on two sides of the initial current sheet, β∞=P∞/(B∞2/2μ0), P∞ is the plasma pressure and B∞ is the magnetic field magnitude far from the current sheet, and trec is the reconnection duration. In the asymmetric case with ρs/ρm=2, β∞=0.01 and trec=1000, the maximum Alfvén Mach number of fast shocks (MA1 max) is MA1 max≅1.1, where MA1=Vn1/VA1, and Vn1 and VA1 are, respectively, the normal upstream fluid velocity and the upstream Alfvén speed in the fast shocks frame. As the density ratio ρs/ρm (=1–8) and plasma beta β∞ (=0.0001–1) increase, MA1 max varies slightly. For the case with a large plasma beta β∞ (=5), the fast shock is very weak. As the reconnection duration trec increases, the bulges lead to generation of fast shocks with a higher MA1 max. The present results can be applied to the mechanism of coronal heating by fast shocks. [ABSTRACT FROM AUTHOR]

In this paper a new method of determining the energy spread of a relativistic electron beam from a laser-driven plasma wakefield accelerator by measuring radiation from an undulator is presented. This could be used to determine the beam characteristics of multi-GeV accelerators where conventional spectrometers are very large and cumbersome. Simultaneous measurement of the energy spectra of electrons from the wakefield accelerator in the 55–70 MeV range and the radiation spectra in the wavelength range of 700–900 nm of synchrotron radiation emitted from a 50 period undulator confirm a narrow energy spread for electrons accelerated over the dephasing distance where beam loading leads to energy compression. Measured energy spreads of less than 1% indicates the potential of using a wakefield accelerator as a driver of future compact and brilliant ultrashort pulse synchrotron sources and free-electron lasers that require high peak brightness beams. [ABSTRACT FROM AUTHOR]

A recent paper [L.-N. Hau and W.-Z. Fu, Phys. Plasmas 14, 110702 (2007)] deals with certain mathematical and physical properties of the kappa distribution. We comment on the authors’ use of a form of distribution function that is different from the “standard” form of the kappa distribution, and hence their results, inter alia for an expansion of the distribution function and for the associated number density in an electrostatic potential, do not fully reflect the dependence on κ that would be associated with the conventional kappa distribution. We note that their definition of the kappa distribution function is also different from a modified distribution based on the notion of nonextensive entropy. [ABSTRACT FROM AUTHOR]

When an ion beam with sharp edge propagates through a background plasma, its current is neutralized by the plasma return current everywhere except at the beam edge over a characteristic transverse distance Δx⊥∼δpe, where δpe=c/ωpe is the collisionless skin depth and ωpe is the electron plasma frequency. Because the background plasma electrons neutralizing the ion beam current inside the beam are streaming relative to the background plasma electrons outside the beam, the background plasma can support a two-stream surface-mode excitation. Such surface modes have been studied previously assuming complete charge and current neutralization, and have been shown to be strongly unstable. In this paper we study the detailed stability properties of this two-stream surface mode for an electron flow velocity profile self-consistently driven by the ion beam. In particular, it is shown that the self-magnetic field generated inside the unneutralized current layer, which has not been taken into account previously, completely eliminates the instability. [ABSTRACT FROM AUTHOR]

The present paper is concerned with analytic models of warm plasma dispersion relations for electromagnetic waves propagating parallel to the ambient magnetic field. Specifically, effects of finite betas on two slow modes, namely, the left-hand circularly polarized ion-cyclotron mode and the right-hand circularly polarized whistler mode, are investigated. Analytic models of the warm plasma dispersion relations are constructed on the basis of conjecture and upon comparisons with numerically found roots. It is shown that the model solutions are good substitutes for actual roots. The significance of the present work in the context of nonlinear plasma research is discussed. [ABSTRACT FROM AUTHOR]

Nondiffusive anomalous momentum transport in toroidal plasmas occurs through symmetry breaking mechanisms. In this paper the contribution of sheared E×B flows to parallel momentum transport [R. R. Dominguez and G. M. Staebler, Phys Fluids B 5, 3876 (1993)] is investigated with nonlinear gyrokinetic simulations in toroidal geometry. The background perpendicular shear is treated independently from the parallel velocity shear to isolate a nondiffusive, nonpinch contribution to the parallel momentum flux. It is found that the size of the term depends strongly on the magnetic shear, with the sign reversing for negative magnetic shear. Perpendicular shear flows are responsible for both symmetry breaking and suppression of turbulence, resulting in a shearing rate at which there is a maximum contribution to the momentum transport. The E×B momentum transport is shown to be quenched by increasing flow shear more strongly than the standard linear quench rule for turbulent heat diffusivity. [ABSTRACT FROM AUTHOR]

The transport of parallel momentum by small scale fluctuations is intrinsically linked to symmetry breaking in the direction of the magnetic field. In tokamaks, an up-down asymmetry in the equilibrium proves to be an efficient parallel symmetry breaking mechanism leading to the generation of a net radial flux of parallel momentum by the electrostatic turbulence [Y. Camenen et al., Phys. Rev. Lett. 102, 125001 (2009)]. This flux is neither proportional to the toroidal rotation nor to its gradient and arises from an incomplete cancellation of the local contributions to the parallel momentum flux under the flux surface average. The flux of parallel momentum then depends on the asymmetry of the curvature drift and on the extension of the fluctuations around the low field side midplane. In this paper, the mechanisms underlying the generation of the flux of parallel momentum are highlighted and the main dependences on plasma parameters investigated using linear gyrokinetic simulations. [ABSTRACT FROM AUTHOR]

In this paper the formation and the dynamics of ion thermal double layers (ITDLs) in a magnetized plasma, composed of positive and negative ions as well as a fraction of stationary charged (positive or negative) dust impurities have been studied. Using plasma hydrodynamics and Poisson equations for the two ion species, a modified Zakharov–Kuznetsov equation has been derived. The effects of the external magnetic field, the concentration of charged dust impurities, and the negative to positive ion temperature ratio on the ITDLs structure are investigated. [ABSTRACT FROM AUTHOR]

To increase the power level of the sources of coherent electromagnetic radiation at frequencies from 100 GHz up to the terahertz range it makes sense to develop devices with a spatially extended interaction space. Sheet-beam and multiple-beam devices belong to the category. In the present paper the small-signal theory of traveling-wave tubes with sheet-beam and multiple sheet-beam configurations is developed. It is shown that in such tubes the wave coupling on electron beams may occur even in small-signal regimes. The wave coupling and its role for amplification of forward and excitation of backward waves in such amplifiers is studied. Also the effect of transverse nonuniformity of the electromagnetic field on the device operation is analyzed and illustrated by several examples. [ABSTRACT FROM AUTHOR]

Velocity distribution functions with an excess of superthermal particles are commonly observed in space plasmas, and are effectively modeled by a kappa distribution. They are also found in some laboratory experiments. In this paper we obtain existence conditions for and some characteristics of ion-acoustic solitary waves in a plasma composed of cold ions and κ-distributed electrons, where κ>3/2 represents the spectral index. As is the case for the usual Maxwell–Boltzmann electrons, only positive potential solitons are found, and, as expected, in the limit of large κ one recovers the usual range of possible soliton Mach numbers, viz., 1

The electron distributions detected in the solar wind feature varying degrees of anisotropic high-energy tail. In a recent work the present authors numerically solved the one-dimensional electrostatic weak turbulence equations by assuming that the solar wind electrons are initially composed of thermal core plus field-aligned counterstreaming beams, and demonstrated that a wide variety of asymmetric energetic tail distribution may result. In the present paper, the essential findings in this work are tested by means of full particle-in-cell simulation technique. It is found that the previous results are largely confirmed, thus providing evidence that the paradigm of local electron acceleration to high-energy tail by self-consistently excited Langmuir turbulence may be relevant to the solar wind environment under certain circumstances. However, some discrepancies are found such that the nearly one-sided energetic tail reported in the numerical solution of the weak turbulence kinetic equation is not shown. [ABSTRACT FROM AUTHOR]

A novel particle simulation code, the electromagnetic spacecraft environment simulator (EMSES), has been developed for the self-consistent analysis of spacecraft-plasma interactions on the full electromagnetic (EM) basis. EMSES includes several boundary treatments carefully coded for both longitudinal and transverse electric fields to satisfy perfect conductive surface conditions. For the longitudinal component, the following are considered: (1) the surface charge accumulation caused by impinging or emitted particles and (2) the surface charge redistribution, such that the surface becomes an equipotential. For item (1), a special treatment has been adopted for the current density calculated around the spacecraft surface, so that the charge accumulation occurs exactly on the surface. As a result, (1) is realized automatically in the updates of the charge density and the electric field through the current density. Item (2) is achieved by applying the capacity matrix method. Meanwhile, the transverse electric field is simply set to zero for components defined inside and tangential to the spacecraft surfaces. This paper also presents the validation of EMSES by performing test simulations for spacecraft charging and peculiar EM wave modes in a plasma sheath. [ABSTRACT FROM AUTHOR]

The behavior of plasma in magnetic field is, as a rule, defined by nonlinear interaction of numerous oscillations and exhibits a complex turbulent pattern. Such state of plasma cannot described by linear and quasilinear theories. This paper reflects on the history of studying turbulence in magnetized plasma. In 1964, Kadomtsev (1928–1998) suggested [B. B. Kadomtsev, Vopr. Teor. Plazmy 4, 188 (1964)] that for estimation of coefficients of turbulent transport of plasma across the magnetic field, only the results of linear approximation of plasma instabilities can be used. Examples of experimental validation of the suggested approach, in particular regarding properties of turbulent positive column of discharge in a strong magnetic field, of ionization turbulence of weakly ionized plasma in crossed E, H, fields, and of turbulence of wall plasma in tokamaks, are discussed. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of the mode structure on the Coriolis pinch effect [A. G. Peeters, C. Angioni, and D. Strintzi, Phys. Rev. Lett. 98, 265003 (2007)]. It is shown that the Coriolis drift effect can be compensated for by a finite parallel wave vector, resulting in a reduced momentum pinch velocity. Gyrokinetic simulations in full toroidal geometry reveal that parallel dynamics effectively removes the Coriolis pinch for the case of adiabatic electrons, while the compensation due to the parallel dynamics is incomplete for the case of kinetic electrons, resulting in a finite pinch velocity. The finite flux in the case of kinetic electrons is interpreted to be related to the electron trapping, which prevents a strong asymmetry in the electrostatic potential with respect to the low field side position. The physics picture developed here leads to the discovery and explanation of two unexpected effects: First the pinch velocity scales with the trapped particle fraction (root of the inverse aspect ratio), and second there is no strong collisionality dependence. The latter is related to the role of the trapped electrons, which retain some symmetry in the eigenmode, but play no role in the perturbed parallel velocity. [ABSTRACT FROM AUTHOR]

This paper presents a set of model collision operators, which reproduce the neoclassical equilibrium and comply with the constraints of a full-f global gyrokinetic code. The assessment of these operators is based on an entropy variational principle, which allows one to perform a fast calculation of the neoclassical diffusivity and poloidal velocity. It is shown that the force balance equation is recovered at lowest order in the expansion parameter, the normalized gyroradius, hence allowing one to calculate correctly the radial electric field. Also, the conventional neoclassical transport and the poloidal velocity are reproduced in the plateau and banana regimes. The advantages and drawbacks of the various model operators are discussed in view of the requirements for neoclassical and turbulent transport. [ABSTRACT FROM AUTHOR]

In earlier works the Krook model for nonlocal electron energy transport in laser produced plasmas was examined. This paper extends the earlier work by treating spherical configurations, specifically laser driven implosions. Additions to the theory due to spherical geometry are worked out. As in the planar case, the nonlocal effects manifest themselves both as flux limitation and preheat. Nonlocal transport does have an effect on the fusion gain of laser pellet implosions. [ABSTRACT FROM AUTHOR]

Period multiplication and chaos behaviors in atmospheric glow discharges are important to understand atmospheric glow plasma stability and to optimize its applications. In this paper, we study the period-two discharge characteristics in argon atmospheric dielectric-barrier discharges using a one-dimension fluid model. Under certain conditions, period-two discharges can occur at different excitation frequencies and exhibit different current and voltage behaviors. When the discharge current becomes highly symmetrical the period-two discharge can reach to a steady state, which sustains over a broad frequency range. At the sufficiently high excitation frequency, the period-two discharge in atmospheric argon shows noticeably different behaviors from the discharges generated at kilohertz frequency. The spatial characteristics of period-two discharge as well as the influence of driving frequency on period-two discharge behaviors are also investigated. [ABSTRACT FROM AUTHOR]

To reduce the dimensions of relativistic backward wave oscillators (RBWOs) operating in the low frequency regime of less than 2 GHz, the theory of transversal and longitudinal mode selections are introduced in this paper. The transversal mode selection is achieved using the property of “surface wave” of the coaxial slow-wave structure (SWS) to excite the quasi transverse electromagnetic (quasi-TEM) mode without the higher transverse magnetic (TM) modes and it is proved that the coaxial SWS may decrease the transversal dimension of the SWS sections. In addition, the S-parameter method is employed to investigate the longitudinal resonant characteristic of the finite-length SWS, and the scheme of longitudinal mode selection is put forward. It is proposed that the introduction of a well-designed coaxial extractor to slow-wave devices can help to achieve the longitudinal mode selection and reduce the period number of the SWS, which not only can make the devices more compact, but also can avoid the destructive competition between various longitudinal modes, therefore can enhance the efficiency and stabilize the frequency. To sum up, the physical mechanisms of transversal and longitudinal mode selections ensure that the microwave is produced with a single mode and a narrow band. Based on the above discussion, a compact L-band coaxial RBWO is investigated and optimized in detail with the particle-in-cell KARAT code (V. P. Tarakanov, Berkeley Research Associates, Inc., 1992). In simulation, the L-band coaxial RBWO, driven by a 700 kV, 11 kA electron beam, comes to a nonlinear steady state in 20 ns. High-power microwave of quasi-TEM mode is generated with an average power of 2.66 GW, a frequency of 1.6 GHz, and power conversion efficiency of 34.5% in durations of 30–60 ns. [ABSTRACT FROM AUTHOR]

It is often assumed that quantum effects will be significant only in the low temperature and high density plasmas. In this paper this assumption is challenged by considering the quantum contribution to the Landau damping of electron plasma waves in normal temperature and high density plasmas. Starting from the linearized Vlasov equation which contains the Bohm quantum potential, the dispersion relation of electron plasma waves propagating in a quantum plasma is derived. A linear Landau damping rate and equations for this process are also deduced. Result indicates that quantum effects enlarge effective frequency of plasmas, which is attributed to an increase in charge or number density of plasma electrons. As a result, Debye length is reduced, and the Debye screening effect becomes obvious. So the quantum behavior appears screening effect here. Landau damping rate is reduced by quantum effects and the exchange of energy between particles and waves is retarded. [ABSTRACT FROM AUTHOR]

A second order Korteweg–deVries (KdV) equation that describes the evolution of nonlinear electrostatic waves in fully relativistic two-fluid plasmas is derived without any assumptions restricting the magnitudes of the flow velocity and the temperatures of each species. In the derivation, the positive and negative species of plasmas are treated with equal footings, not making any species specific assumptions. Thus, the resulting equation, which is expressed in transparent form symmetric in particle species, can be applied to any two-fluid plasmas having arbitrarily large flow velocity and ultrarelativistically high temperatures. The phase velocity of the nonlinear electrostatic waves found in this paper is shown to be related to the flow velocity and the acoustic wave velocity through the Lorentz addition law of velocities, revealing the relativistic nature of the formulation in the present study. The derived KdV equation is applied to some limiting cases, and it is shown that it can be reduced to existing results in nonrelativistic plasmas, while there are some discrepancies from the results in the weak relativistic approximations. [ABSTRACT FROM AUTHOR]

The possibility of the nonlinear decay of a localized perturbation into the ion-acoustic solitons is studied. The present paper is a theoretical attempt to model the experimental soliton excitation [S. Yi et al., Phys. Plasmas 4, 2436 (1997)] in which solitons are excited by a grid modulating near the ion plasma frequency. It has been reported that a localized wave was created near the grid that would decay nonlinearly into the ion-acoustic soliton and a wave packet [T. E. Sheridan et al., Phys. Plasmas 5, 3165 (1998)]. For this purpose, an unbounded plasma composed of the cold positively charged ions and hot electrons is considered. Electron trapping is included in the model as the result of their nonlinear resonant interaction with the localized potential well. A Gaussian initial perturbation is used to model the localized perturbation. The numerical calculation through a modified Korteweg–de Vries equation simulates the decay of the initial Gaussian perturbation into several ion-acoustic solitons and a wave packet. It is shown that the electron trapping has an essential influence on the decay process. [ABSTRACT FROM AUTHOR]

A Zakharov–Kuznetsov (ZK) equation, a modified ZK (mZK) equation, and a coupled ZK (cZK) equation for small but finite amplitude dust acoustic waves in a magnetized two-ion-temperature dusty plasma with dust size distribution have been investigated in this paper. The variations of the linear dispersion relation and group velocity, nonlinear solitary wave amplitude, and width with an arbitrary dust size distribution function are studied numerically. We conclude that they all increase as the total number density of dust grains increases, and they are greater for unusual dusty plasma (the number density of larger dust grains is greater than that of smaller dust grains) than that of usual dusty plasma (the number density of smaller dust grains is greater than that of larger dust grains). It is noted that the frequency of the linear wave increases as the wave number along the magnetic direction increases. Furthermore, the width of the nonlinear waves increases but its amplitude decreases as the wave number along the magnetic direction increases. [ABSTRACT FROM AUTHOR]

This paper presents the model equation governing the nonlinear dynamics of the kinetic Alfvén wave (KAW) in the low-β plasmas (β≪me/mi) and intermediate-β plasmas (me/mi≪β≪1), where β is thermal pressure to background magnetic pressure ratio, me/mi is the electron to ion mass ratio. When the ponderomotive and Joule heating nonlinearities are incorporated in the KAW dynamics, the model equation turns out to be a modified nonlinear Schrödinger equation. Numerical solution of this has been obtained when the incident pump KAW is having a small perturbation. Energy exchange between main KAW and perturbation and the resulting filamentary structures of the KAW have been studied. More detail diagnostics reveal that the dynamics of the wave is chaotic. We have presented a simplified model also to explain some of the features of this evolution. Nonlinear saturation of the instability in the form of localized structures and the resulting power spectra of the magnetic field has also been studied. [ABSTRACT FROM AUTHOR]

In recent experiments of strongly coupled complex plasmas (SCCPs), trapping-like phenomena of micro-sized dust particles were observed during propagation of large-amplitude dust-density waves. A small number of particles were observed being trapped and carried along with the waves. In the present paper, we study the similar trapping phenomena in two-dimensional SCCPs by using Brownian dynamics simulation. The trapping process and its new features arising from strong-coupling effects are investigated. In particular, similarities and differences between trapping in weakly coupled plasmas and SCCPs are discussed in detail. [ABSTRACT FROM AUTHOR]

A one-dimensional version of the second-order transition model based on the sheared flow amplification by Reynolds stress and turbulence suppression by shearing is presented. The model discussed in this paper includes a form of the Reynolds stress which explicitly conserves momentum. A linear stability analysis of the critical point is performed. Then, it is shown that the dynamics of weakly unstable states is determined by a reduced equation for the shear flow. In the case in which the flow damping term is diffusive, the stationary solutions are those of the real Ginzburg-Landau equation. [ABSTRACT FROM AUTHOR]

A physical mechanism and nonlinear mathematical formalism for study of generation and further amplification of the vortical electric field in the magnetized plasma are proposed. A modulation instability process in a plasma medium is considered in a strong constant magnetic field. The plasmon condensate is modulated not by a low-frequency ionic sound as is usually done, but by the beating of two high-frequency transverse electromagnetic waves propagating along the external magnetic field. Conditions in which aperiodic instability occurs are found and its increment is defined. This instability leads to a decrease in the scale of Langmuir turbulence along the external magnetic field and to the generation of electromagnetic fields. Dissipative property of the medium increases an amplitude threshold of the pumping waves. It is shown that for sufficiently large amplitudes of pumping waves the effect described in the paper is the defining nonlinear process. [ABSTRACT FROM AUTHOR]

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

An electron injector concept for a laser-plasma accelerator was developed by E. Esarey et al. [Phys. Rev. Lett. 79, 2682 (1997)] and G. Fubiani et al. [Phys. Rev. E 70, 016402 (2004)]; it relies on the use of counterpropagating ultrashort laser pulses. In the latter work, the scheme is as follows: the pump laser pulse generates a large-amplitude laser wakefield (plasma wave). The counterpropagating injection pulse interferes with the pump laser pulse to generate a beatwave pattern. The ponderomotive force of the beatwave is able to inject plasma electrons into the wakefield. In this paper, this injection scheme is studied using one-dimensional Particle-in-Cell simulations. The simulations reveal phenomena and important physical processes that were not taken into account in previous models. In particular, at the collision of the laser pulses, most plasma electrons are trapped in the beatwave pattern and cannot contribute to the collective oscillation supporting the plasma wave. At this point, the fluid approximation fails and the plasma wake is strongly inhibited. Consequently, the injected charge is reduced by one order of magnitude compared to the predictions from previous models. [ABSTRACT FROM AUTHOR]

This paper reviews the concepts, recent history, and current challenges for realizing ultracompact particle accelerators based on surfing on plasma waves. Ideas that seemed fanciful when first proposed by John Dawson in the late 1970s have now come to fruition as a result of the development of ultrashort high-power laser and particle beam drivers, tunnel-ionized plasma sources, and one-to-one particle simulation capability. Breakthroughs in the past 2 years have dramatically advanced the field. Laser-driven gas jets now produce 100 MeV beams of electrons that are monoenergetic and that have transverse beam quality and brightness exceeding that in conventional accelerators. Electron-beam driven plasma waves driven by the 28 GeV electron beam of the Stanford Linear Accelerator Center have been used to accelerate electrons in the tail of the beam by more than 10 GeV in less than 30 cm. The prospects for extending both of these schemes to the energy frontier (currently 50 GeV) and beyond are discussed. [ABSTRACT FROM AUTHOR]

Plasma neutralization of an intense ion pulse is of interest for many applications, including plasma lenses, heavy ion fusion, cosmic ray propagation, etc. An analytical electron fluid model has been developed to describe the plasma response to a propagating ion beam. The model predicts very good charge neutralization during quasi-steady-state propagation, provided the beam pulse duration τb is much longer than the electron plasma period 2π/ωp, where ωp=(4πe2np/m)1/2 is the electron plasma frequency, and np is the background plasma density. In the opposite limit, the beam pulse excites large-amplitude plasma waves. If the beam density is larger than the background plasma density, the plasma waves break. Theoretical predictions are compared with the results of calculations utilizing a particle-in-cell (PIC) code. The cold electron fluid results agree well with the PIC simulations for ion beam propagation through a background plasma. The reduced fluid description derived in this paper can provide an important benchmark for numerical codes and yield scaling relations for different beam and plasma parameters. The visualization of numerical simulation data shows complex collective phenomena during beam entry and exit from the plasma. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The inhomogeneous plasma parametric decay instability (PDI) is studied in the present paper both experimentally and theoretically for different types of pump wave frequency modulation. It is shown that the theory conclusion on weak sensitivity of inhomogeneous plasma PDI to the pump frequency modulation holds only for modulation faster than the decay wave transient time. In the case of slower modulation, both harmonic and stochastic, the PDI resonant enhancement may take place instead. The expression for amplification in the resonance is derived and several mechanisms of the singularity saturation are studied. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The theory of beat wave excitation in a slightly inhomogeneous plasma is presented. While the theory is general it applies directly to the experiments performed in Alaska by the ionospheric heating facilities HIPAS [High Power Auroral Simulation, Radio Sci. 25, 1269 (1990)] and HAARP [High Frequency Active Auroral Research Project, Geophys. Res. Lett. 25, 257 (1998)]. A ray tracing (WKB) formalism appropriate for computations is developed. The computational implementation of this formalism and extensive results will be presented in a follow up to this paper. Also the beat wave excitation of upper-hybrid waves is investigated analytically. The complicated trajectories of these waves in the plasma are described. When this beat wave reaches the plasma wave resonance it can, in the HIPAS-HAARP experiments, attain nonlinear amplitude. The electrostatic upper-hybrid waves are trapped around the density maximum of the ionosphere. This trapping is investigated in detail. Beat wave pumping of the trapped modes is possible using HAARP and HIPAS or with split beams from HAARP. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A theoretical and experimental study of Trivelpiece–Gould waves propagating in a magnetized plasma column is presented in this paper. In the experiments, these waves are excited by a radio frequency (rf) source, which also serves to create the plasma. Observation of nonlinear effects includes space and time recurrence effects, a wave spectrum containing a large number (up to 25) harmonics, and low-frequency sidebands. The theoretical model explains the recurrence effects as a consequence of multiple nonlinear interactions between the fundamental wave and its harmonics. A good agreement is found between theory and the experiments. [ABSTRACT FROM AUTHOR]

When an electromagnetic wave is linearly converted into an electrostatic wave, large enhancement of the wave amplitude occurs, due to the large ratio between the group velocities. The objective of this paper is to study the structure of the electrostatic wave field when such a mode conversion takes place in a magnetized plasma, and compare the amplitude enhancement with that of an unmagnetized plasma. In a magnetized plasma, the electric field of an electrostatic wave in the plasma resonance region is in the generic case governed by a third-order differential equation first discussed by Piliya and Fedorov [Zh. Eksp. Teor. Fiz. 57, 1198 (1969)]. The validity and interpretation of this equation is discussed. Full wave solutions obtained numerically are exhibited, and compared with the unmagnetized case. In particular, scaling laws describing how the maximum electric field amplitude for given energy flux depends on the magnetic field parameters are obtained. [ABSTRACT FROM AUTHOR]