Quantum-kinetic calculation for net acceleration of high-energy electrons by a transverse undulating magnetic field and an electromagnetic wave

The average force acting on a highly relativistic electron beam traveling in a laser wave and a transverse undulating magnetic field (magnetic wiggler) is calculated using quantum kinetics. The quantum-kinetic calculation shows that the net dc force due to net inverse bremsstrahlung in the magnetic wiggler (“inverse free electron lasing”) increases linearly with the beam energy, and can be greater than the Lorentz force of the laser wave.     

High intensity laser plasma interaction

Basic mechanisms, linear and non-linear, are reviewed. Light absorption may take place linearly through inverse bremsstrahlung. Together with usual heat transport by electrons it leads to a linear gas dynamical regime whose main formulas are given. When absorption occurs non-linearly, by resonance in a density gradient or through wave-wave couplings, several non-linear regimes may show up. They are investigated in connection with the ponderomotive force, soliton formation, wavebreaking, … The processes responsible for harmonic generation are given special developments.     

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.     

Feasibility of a plasma-filled inverse free electron laseraccelerator

A high power millimeter (mm) wave, in the presence of a magnetic wiggler, produces a large longitudinal ponderomotive force that can accelerate electrons. When a plasma of density n~n_cr, where n _cr is critical density, is introduced in the interaction region, the ponderomotive force resonantly drives a plasma wave that accelerates electrons to higher energies. However, propagation of the mm wave requires a guide magnetic field; O-mode requiring less field than the X-mode. The plasma wave in this situation goes over to the upper hybrid (UH) mode. A parabolic plasma density profile with minimum on axis provides guiding for the mm wave as well as the UH wave, the latter being more strongly localized than the former. The UH wave, for typical parameters, can accelerate electrons to several tens of megaelectronvolts     

Net acceleration of high-energy electrons by net inverse Bremsstrahlung of a laser wave in a uniform magnetic field and a transverse undulating magnetic field

The nonzero net dc force acting on relativistic beam electrons traveling in a uniform magnetic field, a laser wave, and transverse undulating magnetic field (magnetic wiggler) is calculated by using quantum-kinetics in accordance with the correspondence principle. It is found that the average of this force can be as strong as the Lorentz force of the laser wave in an electron energy region beyong energies for free electron lasing, and decreases linearly with the inverse of the electron energy far beyond this energy region.     

Relativistic Derivation of the Ponderomotive Force Produced by Two Intense Laser Fields

The ponderomotive force plays a fundamental role in the absorption of laser light on self-consistent plasma density profiles, in multiple-photon ionization, and in intense field electrodynamics. The relativistic corrections to the ponderomotive force of a transversely polarized electromagnetic wave lead to an approximately 20-percent reduction in the single particle ponderomotive force produced by a 10-?m 1016-W/cm2 laser field. Recent experimental investigations are based on using two intense laser fields to produce desired laser-matter interactions. This paper presents the first derivation of the nonlinear relativistic ponderomotive force produced by two intense laser fields. The results demonstrate that relativistic ponderomotive forces are not additive.     

Wavenumber oscillations of a linear electron plasma testwave in the presence of a standing large-amplitude wave

A linear electron plasma testwave coexisting with a standing large-amplitude wave shows wavenumber oscillations which may be explained by stationary axial plasma density variations being produced by the pump wave via the ponderomotive force.     

Ionization by a pulsed plasma surface wave

The ionization mechanism is studied of a pulsed surface wave generating a microwave discharge. When the plasma is dominated by collisions, it is found that the velocity of the ionization front depends on the ponderomotive force due to the field gradient in the front.     

Stabilization effect of Weibel modes due to inverse bremsstrahlung absorption in laser fusion plasma using Krook collisions model

In this work, the Weibel instability due to inverse bremsstrahlung absorption in laser fusion plasma has been investigated. The stabilization effect due to the coupling of the self-generated magnetic field by Weibel instability with the laser wave field is explicitly showed. The main result obtained in this work is that the inclusion of self-generated magnetic field due to Weibel instability to the inverse bremsstrahlung absorption causes a stabilizing effect of excited Weibel modes. We found a decrease in the spectral range of Weibel unstable modes. This decrease is accompanied by a reduction of two orders in the growth rate of instability or even stabilization of these modes. It has been shown that the previous analyses of the Weibel instability due to inverse bremsstrahlung have overestimated the values of the generated magnetic fields. Therefore, the generation of magnetic fields by the Weibel instability due to inverse bremsstrahlung should not affect the experiences of an inertial confinement fusion.     

Quantum effects on magnetization due to ponderomotive force in cold quantum plasmas

The quantum effects on the magnetization due to the ponderomotive force are investigated in cold quantum plasmas. It is shown that the ponderomotive force of the electromagnetic wave induces the magnetization and cyclotron motion in quantum plasmas. We also show that the magnetic field would not be induced without the quantum effects in plasmas. It is also found that the quantum effect enhances the cyclotron frequency due to the ponderomotive force related to the time variation of the field intensity. In addition, it is shown that the magnetization diminishes with an increase of the frequency of the electromagnetic field.     

Ponderomotive transport of a variable-charge granule in a dusty plasma in the field of an intense ion-sound wave

The ponderomotive force acting on a variable-charge granule in a dusty plasma from an intense ion-sound wave is considered. Allowance for oscillations of the granule charge in the field of an ion-sound wave makes it possible to reveal new components of this force that are proportional to the wave vector of the field and the cube of its amplitude. These components do not vanish in the case of a uniform field and also lead to a directed transport of the dust plasma fraction.     

Fully relativistic theory of the ponderomotive force in an ultraintense standing wave

A relativistic field-gradient (ponderomotive) force in a laser standing wave ceases to exist in a familiar form; e.g., the adiabatic Hamiltonian is not separable into kinetic and potential energies for electrons moving in the antinode planes. We show that the force in the direction across the initial motion of an electron reverses its sign and makes the high-field areas attractive for electrons, opposite to a regular ponderomotive force. The reversal occurs at a relativistic-scale incident momentum, and represents the only effect known so far that pins down a distinct borderline between relativistic and nonrelativistic motion.     

Cross-focusing of two laser beams in a plasma

Cross-focusing of two copropagating laser beams in a plasma is investigated using paraxial ray theory. If the lasers have a frequency difference equal to the electron plasma frequency, they can drive a large amplitude plasma wave. The ponderomotive force due to the plasma wave forces the plasma electrons outwards thereby generating a parabolic density profile giving rise to cross-focusing. The results show a decrease in threshold for focusing by two orders of magnitude as compared to focusing due to the ponderomotive force of the laser beams.     

Microwave ponderomotive action on the inhomogeneous collisionless and collisional plasmas

The nonlinear interaction of a high-power microwave (MW) with an unmagnetized inhomogeneous plasma is investigated in collisionless and collisional regimes. The electron density distribution and the nonlinear wave equation in an inhomogeneous plasma are obtained by taking into account the ponderomotive force due to the high-power MW. It is shown that the electron density distribution becomes very steepened in the presence of the ponderomotive force. In the collisional regime, the expression for electron temperature is also found by considering ohmic heating. It is indicated that the amplitude of oscillations of the electron temperature and dielectric permittivity increases and the wavelength of these oscillations decreases with increasing energy flux, hence modulation occurs.     

Stochastic Behavior of Particles in a Circularly Polarized Standing Wave

The particle motion in a standing left circularly polarized wave is studied. For wave frequency lower than the ion cyclotron frequency ?ci, the slow varying trajectory is given by the ponderomotive force FNL=q2?|E|2/[m?(?-?ci)]. However, for ? close to ?ci, stochastic trajectories occur. These stochastic trajectories are due to the overlapping of closed orbits due to each of the propagating waves which form the standing wave.     

Relativistic ponderomotive forces

The interaction of a relativistic classical electron with an inhomogeneous electromagnetic field is investigated. In second-order perturbation theory the motion is separated into fast and slow motions, and the relativistic Newtonian equation is averaged over the fast oscillations. The rate of change obtained for the slow component of the electron momentum is interpreted as a relativistic ponderomotive force. The result is generalized to the relativistic case of the wellknown expression for the Gaponov-Miller force acting on an electron at rest. The expressions obtained for the relativistic ponderomotive forces are very complicated in the general case. They simplify in the limit of a stationary field (pulses of long duration) and a small gradient. The most typical and simplest special case of an inhomogeneous field—a stationary plane-focused beam—is investigated. The main difference between relativistic ponderomotive forces and their nonrelativistic limit is they have multiple components. In addition to the usual force directed along the gradient of the field, the relativistic case is also characterized by force components that do not have the form of the gradient of a potential and are parallel to the wave vector and the direction of the field polarization. It is shown that when a relativistic electron travels in a direction close to the direction of the wave vector of a focused laser beam, these components can greatly exceed the gradient force. A force directed along the field polarization vector arises even when the gradient of the field in this direction is zero. Zh. éksp. Teor. Fiz. 116, 1198–1209 (October 1999)     

Ponderomotive Force Effects due to a Circularly Polarized Electromagnetic Wave

The modifications in the time-averaged plasma particle distribution functions in the presence of a large amplitude electromagnetic wave are studied. It is shown that the ponderomotive force is responsible for tail formation, non-zero particle currents and heat fluxes. Explicit results, which describe those effects, are derived.     

Ponderomotive effects in intense pumping wave action on electron and plasma bunches

Ponderomotive effects that arise when an intense plane pumping wave acts on low-concentration electron and plasma bunches are theoretically studied within the framework of a one-dimensional model. Using the Lagrange variables, an electron (plasma) bunch under the action of a pumping field can be represented as a gas comprising macroparticles with ponderomotive and Coulomb interactions. The ponderomotive force at small interparticle distances is attractive, that is, directed oppositely to the Coulomb force; it cannot, however, completely balance the latter. The constructed model is used to study superradiance, which arises when an intense pumping wave acts on an extended electron bunch. Radiation is then scattered in the form of narrow pulses whose amplitude is proportional to the total number of particles in the bunch. In addition, we describe acceleration of a neutral plasma layer, narrow on the wavelength scale, in the field of an intense wave and radiation field-induced partial contraction of an electron bunch with an incompletely compensated charge.     

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.     

Nonlinear propagation of neutrinos in a strongly magnetized medium

The nonlinear propagation of an intense neutrino flux in an electron-positron plasma with equilibrium density and magnetic field inhomogeneities is considered. It is found that the neutrinos are nonlinearly coupled with electrostatic and electromagnetic disturbances due to weak Fermi interaction and ponderomotive forces. The process is governed by a Klein-Gordon equation for the neutrino flux and a wave equation for the plasma oscillations in the presence of the ponderomotive force of the neutrinos. This pair of equations is then used to derive a nonlinear dispersion relation which exhibits that nonthermal electrostatic and electromagnetic fluctuations are created on account of the energy density of the neutrinos. The relevance of our investigation to the anomalous absorption of neutrinos in a nonuniform magnetized medium is pointed out.