Equilibrium profiles for RF-plasma sources with ponderomotiveforces

An analysis is given of the influence of the electron ponderomotive force on the equilibrium plasma profiles of partially ionized, radio frequency discharge sources, The ponderomotive force can be written as a gradient of a potential varying with the square of the RF field in the plasma and is largest for electrons, The impact of this electron ponderomotive force on density and electrostatic potential profiles is demonstrated using a one-dimensional analytic model with supporting numerical solutions and a two dimensional fluid simulation. For nearly collisionless plasmas the ponderomotive force is valid when ω_ce^h/ω<1 where ω_ce ^h is the electron cyclotron frequency due to the RF magnetic field and ω is the RF driving frequency, In processing plasmas with parameters that satisfy this validity criteria, the equilibrium density profiles are weakly modified, For nearly collisionless processing plasmas with parameters such that ω_ce^h /ω>1, the ponderomotive force, is modified by other nonlinear force terms that need to be evaluated     

Generation of magnetic fields by the non-stationary ponderomotive force of electromagnetic waves in plasmas with streaming electrons

It is shown that the non-stationary ponderomotive force of large amplitude electromagnetic waves in plasmas with streaming electrons can spontaneously create magnetic fields. The present result may account for the magnetic fields in laser-produces plasmas, in cosmic plasmas, as well as in galactic and inter-galactic spaces.     

Ion acceleration by the space charge electric force arising from the radiation pressure in a magnetized electron–positron plasma

It is shown that ions can be accelerated by the space charge electric force arising from the separation of electrons and positrons due to the ponderomotive force of the magnetic field-aligned circularly polarized electromagnetic (CPEM) wave in a magnetized electron–positron–ion plasma. The ion acceleration critically depends on the external magnetic field strength. The result is useful in understanding differential ion acceleration in magnetized electron–positron–ion plasmas, such as those in magnetars and in some laboratory experiments that aim to mimic astrophysical environments.     

Electron acceleration by net inverse bremsstrahlung of a laser wave in a uniform magnetic field and longitudinal electric waves

The nonzero net dc (ponderomotive force) acting on high-energy beam electrons due to net inverse bremsstrahlung (the absorption by inverse bremsstrahlung minus the emission by stimulated bremsstrahlung) of the electromagnetic wave in a uniform magnetic field and longitudinal electric waves is calculated by using quantum kinetics in accordance with the correspondence principle. It is found that the ponderomotive force can be far stronger than the Lorentz force of the laser wave for an electron-energy range far beyond the free electron lasing regime.     

Nonlinear interaction of the radiation with the pondermotive force deformated plasmas

The interaction of the powerful p-polarised radiation with the plasmas is studied. It is obtained the picture of the space and time evolution of the electromagnetic field in the plasmas and the picture of the particle's redistribution connected with the ponderomotive force of the plasma field and with the hydrodynamic motion as well. The dynamics of the electromagnetic field absorption and the distribution of the absorbed energy between the cold and hot electrons are investigated. The role of such general processes in the effect of second harmonic generation is demonstrated.     

Dynamical behaviour of transverse plasmons in pair plasmas

This paper analytically investigates the nonlinear behaviour of transverse plasmons in pair plasmas on the basis of the nonlinear governing equations obtained from Vlasov--Maxwell equations. It shows that high frequency transverse plasmons are modulationally unstable with respect to the uniform state of the pair plasma. Such an instability would cause wave field collapse into a localized region. During the collapse process, ponderomotive expulsion is greatly enhanced for the increase of wave field strength, leading to the formation of localized density cavitons which are significant for the future experimental research in the interaction between high frequency electromagnetic waves and pair plasmas.     

Magnetic field generation from Alfven waves propagating along helical lines of force

A static induced magnetization of Alfven waves (IMAW) due to the inverse Faraday effect is defined and studied. The Alfven waves are assumed to propagate along helical lines of force of a force-free ambient magnetic field. This induced magnetization follows from the magnetic moment of ordered gyrating motion of charges in the presence of electromagnetic waves and an ambient field. The helicity of the force-free field is found to decrease due to this IMAW. This effect is expected to be important in the physics of magnetization of the sun and pulsars, and also in laboratory devices for the generation of plasmas and their heating.     

The time-dependent ponderomotive force

In this paper, we review stress tensor, fluid theory, kinetic and Lie transform approaches for determining the ponderomotive force induced by high-frequency wavepackets in plasmas. After outlining the historical development of the ponderomotive force, stress tensor approaches will be presented. Here important concepts such as split-ups and symmetry of the stress tensors will be discussed. In the next section we compare several fluid theory derivations. Here the plasma dynamics is described in the oscillation-centre picture and necessitates the introduction of a velocity renormalization in the momentum equation. Next kinetic approaches of ponderomotive forces in Vlasov plasmas will be presented. Single-particle and Lie transform methods are then presented. Here we derive the ponderomotive forces and the wave-induced magnetization current from the ponderomotive Hamiltonian. Finally we discuss the present status of the ponderomotive force and suggest topics for further research.     

Ponderomotive nongradient force acting on a relativistic particle crossing an inhomogeneous electromagnetic wave

The ponderomotive force acting on a relativistic charged particle crossing an inhomogeneous electromagnetic wave is investigated numerically and analytically. The initial velocity of the particle is perpendicular to the electric field vector of the wave and to the direction of its propagation. The wave has zero gradient in the direction of propagation and is inhomogeneous in both transverse directions. It is shown that the ponderomotive force acting on the particle is parallel to the wave vector. The magnitude of the force is determined not only by the extent of wave inhomogeneity in the direction of the translational motion of particle, but also by its inhomogeneity in the transverse direction. It is found that the trajectory of a particle is determined by the action of ponderomotive forces as well as by its drift in a nonuniform field.     

Chirping and spreading of ultrashort laser pulses in underdense plasmas

A linear theory on the propagation of ultrashort pulses including only a few cycles in underdense plasmas is presented. It is shown that the dispersion in plasmas causes severe distortions in the pulse shape, including pulse chirping and spreading. The analytical calculations coincide very well with those obtained by particle-in-cell (PIC) simulations. The upper limit of the peak amplitude of the pulses, above which the linear theory breaks down due to the setting in of nonlinear effects of both the relativistic electron-mass increase and ponderomotive force, is also examined by PIC simulations. At certain high amplitudes, it is found that the ultrashort laser pulses can propagate like solitons.     

Ion larmour radius effect on rf ponderomotive forces and induced poloidal flow in tokamak plasmas

Analytical approximations are used to clarify the effect of Larmour radius on rf ponderomotive forces and on poloidal flows induced by them in tokamak plasmas. The electromagnetic force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation. The first part, called the gradient electromagnetic stress force, is combined with fluid dynamic (Reynolds) stress force, and gyroviscosity is included into viscosity force to model finite ion Larmour radius effects in the momentum response to the rf fields in plasmas. The expressions for the relative magnitude of different forces for kinetic Alfven waves and fast waves are derived.     

The Ponderomotive Force on a Charge q,Moving in an Electromagnetic Field

Equations of motion of a single charged particle are derived to second order in E where E is an electromagnetic field. By averaging over the wave-period we find the ponderomotive force on the particle. This force may lead to a transport of matter as is also the case in ordinary hydrodynamics. There the effect is called acoustic streaming. We also suggest that the well-known Landau damping may be considered as beeing due to a ponderomotive force.     

Quantum Kinetic Theory for Laser Plasmas. Dynamical Screening in Strong Fields

A quantum kinetic theory for correlated charged-particle systems in strong time-dependent electromagnetic fields is developed. Our approach is based on a systematic gauge-invariant nonequilibrium Green's functions formulation. Extending our previous analysis [1] we concentrate on the selfconsistent treatment of dynamical screening and electromagnetic fields which is applicable to arbitrary nonequilibrium situations. The resulting kinetic equation generalizes previous results to quantum plasmas with full dynamical screening and includes many-body effects. It is, in particular, applicable to the interaction of dense plasmas with strong electromagnetic fields, including laser fields and x-rays. Furthermore, results for the modification of the plasma screening and the longitudinal field fluctuations due to the electromagnetic field are presented.     

Excitation of multiple wakefields by short laser pulses in quantum plasmas

We present a theoretical investigation of the excitation of multiple electrostatic wakefields by the ponderomotive force of a short electromagnetic pulse propagating through a dense plasma. It is found that the inclusion of the quantum statistical pressure and quantum electron tunneling effects can qualitatively change the classical behavior of the wakefield. In addition to the well-known plasma oscillation wakefield, with a wavelength of the order of the electron skin depth (λe=c/ωpe, which in a dense plasma is of the order of several nanometers, where c is the speed of light in vacuum and ωpe is the electron plasma frequency), wakefields in dense plasmas with a shorter wavelength (in comparison with λe) are also excited. The wakefields can trap electrons and accelerate them to extremely high energies over nanoscales.     

Compression of laser radiation in plasmas using electromagnetic cascading

Compressing high-power laser beams in plasmas via generation of a coherent cascade of electromagnetic sidebands is described. The technique requires two copropagating beams detuned by a near-resonant frequency Omega approximately < omega(p). The ponderomotive force of the laser beat wave drives an electron plasma wave which modifies the refractive index of plasma so as to produce a periodic phase modulation of the laser field with the beat period tau(b) = 2pi/Omega. A train of chirped laser beat notes (each of duration tau(b)) is thus created. The group velocity dispersion of radiation in plasma can then compress each beat note to a few-laser-cycle duration. As a result, a train of sharp electromagnetic spikes separated in time by tau(b) is formed. Depending on the plasma and laser parameters, chirping and compression can be implemented either concurrently in the same plasma or sequentially in different plasmas.     

Resonant Joule phenomena in a magnetoplasma

The present state of research of resonant Joule interactions of collisional plasmas with electromagnetic waves, including both the problems of plasma heating and wave dynamics, is reviewed. The controlled development of non-linear wave processes in gaseous and solid-body plasmas in radiowave and microwave ranges via resonant heating is discussed. The series of thermal bistability effects, produced by electron-temperature hysteresis near Langmuir and cyclotron resonances, is considered. The geometrical resonances of absorption in layered structures and bounded volumes are illustrated. Localization of dissipation phenomena near resonant regions in heterogeneous and anisotropic magnetoplasmas is analyzed. Relativistic and quantum effects in resonant collisional attenuation of waves in a plasma are shown. Some analogous tendencies in Joule wave phenomena are marked in plasmas characterized by very different physical conditions-from laboratory devices up to cosmic objects.     

Extraordinary Electromagnetic Waves in Weakly Relativistic Degenerate Spin-1/2 Magnetized Quantum Plasmas

By using the relativistic quantum magnetohydrodynamic model, the extraordinary electromagnetic waves in magnetized quantum plasmas are investigated with the effects of particle dispersion associated with the quantum Bohm potential effects, the electron spin-1/2 effects, and the relativistic degenerate pressure effects. The electrons are treated as a quantum and magnetized species, while the ions are classical ones. The new general dispersion relations are derived and analyzed in some interesting special cases. Quantum effects are shown to affect the dispersion relations of the extraordinary electromagnetic waves. It is also shown that the relativistic degenerate pressure effects significantly modify the dispersive properties of the extraordinary electromagnetic waves. The present investigation should be useful for understanding the collective interactions in dense astrophysical bodies,such as the atmosphere of neutron stars and the interior of massive white dwarfs.     

High-frequency surface waves in quantum plasmas with electrons relativistic degenerate and exchange-correlation effects

The propagation characteristics of high-frequency surface waves are studied in spin-1/2 quantum plasmas by considering the electron relativistic degenerate and exchange-correlation effects. Using the quantum fluid equations of magnetoplasmas in the presence of the quantum Bohm potential, spin magnetization energy, relativistic degenerate pressure, and exchange-correlation effects, a generalized dispersion relation is derived. The analytical and numerical results show that the relativistic degenerate and exchange-correlation effects significantly modify the propagation properties of high-frequency surface waves. It is found that under the influence of exchange-correlation effects, the frequency spectrum of high-frequency surface waves will be down-shifted. It is also indicated that the dispersion curve shifts up with the increase of relativistic gamma factor. Furthermore, the phase speed of the high-frequency surface waves increases with increasing electron number density. The current research is helpful to understand the propagation of the high-frequency surface waves in quantum plasmas, such as those in dense astrophysical environment.     

Light magnetoabsorption in systems with quantum confinement in the field of resonant laser radiation

Near-gap light magnetoabsorption is investigated in systems with quantum confinement in the presence of IR laser radiation. It is shown that if the frequency of laser radiation is equal to the cyclotron frequency, the magnetoabsorption line shape can be fully determined by the IR radiation intensity. The frequency dependence of interband absorption of a weak electromagnetic wave can be changed significantly in the case where the laser radiation frequency is equal to the quantum-confinement frequency in parabolic quantum wells and the polarization vector is parallel to the confinement axis.     

Arbitrary magnetosonic solitary waves in spin 1/2 degenerate quantum plasma

Linear and nonlinear compressional magnetosonic waves are studied in magnetized degenerate spin-1/2 Fermi plasmas. Starting from the basic equations of a quantum magnetoplasma we develop the system of quantum magnetohydrodynamic (QMHD) equations. Spin effects are incorporated via spin force and macroscopic spin magnetization current. Sagdeev potential approach is employed to derive the nonlinear energy integral equation which admits the rarefactive solitary structure in the subAlfvenic region. The quantum diffraction due to Bohm potential does not affect the amplitude of soliton but has a direct effect on its width. The width of soliton is broadened with the increase in the quantization of the system due to quantum diffraction. However, the nonlinear wave amplitude is reduced with the increase in the value of magnetization energy due to electron spin-1/2 effects. The degeneracy effect due to quantum plasma beta enhances the amplitude of magnetosonic soliton. The importance of the work relevant to compact astrophysical bodies is pointed out.