Showing papers on "Relativistic plasma published in 1994"
TL;DR: In this paper, the results of an analytical description and of a particle-in-cell simulation of the interaction of an ultrashort, relativistically intense laser pulse, obliquely incident on a nonuniform overdense plasma, are presented and several novel features are identified.
Abstract: The results of an analytical description and of a particle‐in‐cell simulation of the interaction of an ultrashort, relativistically intense laser pulse, obliquely incident on a nonuniform overdense plasma, are presented and several novel features are identified. The absorption and reflection of the ultraintense electromagnetic laser radiation from a sharp‐boundary plasma, high harmonic generation, and the transformation into low‐frequency radiation are discussed. In the case of weak plasma nonuniformity the excitation of nonlinear Langmuir oscillations in the plasma resonance region and the resulting electron acceleration are investigated. The vacuum heating of the electrons and the self‐intersection of the electron trajectories are also studied. In the case of a sharp‐boundary plasma, part of the energy of the laser pulse is found to be converted into a localized, relativistically strong, nonlinear electromagnetic pulse propagating into the plasma. The expansion of the hot electron cloud into the vacuum region and the action of the ponderomotive force of the laser pulse in the localized longitudinal electric field of the Langmuir oscillations lead to ion acceleration. The energy increase of a minority population of multicharged ions is found to be much greater than that of the ambient ions.
403 citations
TL;DR: In this article, it was shown that the charged particles can be trapped by relativistic plasma waves, a necessary condition for obtaining the maximum amount of energy theoretically possible for such schemes.
Abstract: THE aim of new approaches for high-energy particle acceleration1 is to push the acceleration rate beyond the limit (∼100 MeV m−1) imposed by radio-frequency breakdown in conventional accelerators. Relativistic plasma waves, having phase velocities very close to the speed of light, have been proposed2–6 as a means of accelerating charged particles, and this has recently been demonstrated7,8. Here we show that the charged particles can be trapped by relativistic plasma waves—a necessary condition for obtaining the maximum amount of energy theoretically possible for such schemes. In our experiments, plasma waves are excited in a hydrogen plasma by beats induced by two collinear laser beams, the difference in whose frequencies matches the plasma frequency. Electrons with an energy of 2 MeV are injected into the excited plasma, and the energy spectrum of the exiting electrons is analysed. We detect electrons with velocities exceeding that of the plasma wave, demonstrating that some electrons are 'trapped' by the wave potential and therefore move synchronously with the plasma wave. We observe a maximum energy gain of 28 MeV, corresponding to an acceleration rate of about 2.8 GeV m−1.
121 citations
TL;DR: In this article, an analytical and numerical study of the evolution of the Weibel instability in relativistically hot electron-positron plasmas is presented, where appropriate perturbations on the electromagnetic fields and the particle orbits are determined analytically and used as initial conditions in the numerical simulations to excite a single unstable mode.
Abstract: Analytical and numerical studies of the evolution of the Weibel instability in relativistically hot electron–positron plasmas are presented. Appropriate perturbations on the electromagnetic fields and the particle orbits, corresponding to a single unstable mode, are determined analytically and used as initial conditions in the numerical simulations to excite a single unstable mode. A simple estimate of the saturation amplitude is also obtained analytically. Numerical simulations are carried out when a single unstable mode is favorably excited. Comparisons of the simulation results with the analytical ones show very good agreement. Also observed in the simulations are mode competition, mode suppression, and the difference in the long‐term evolution between the magnetized and unmagnetized plasmas. For relativistic unmagnetized plasmas, energy‐like global constraints, which are conservation laws in addition to the conservation of energy and momentum, are derived. Numerical simulations of the multimode evolut...
79 citations
TL;DR: If the out flow velocity from the resistive region approaches the relativistic Alfven speed, the outflow density increase from Lorentz contraction allows a much faster inflow and thus a faster rate of magnetic energy dissipation than in the nonrelativistic regime.
Abstract: We study the relativistic generalizations of two-dimensional Sweet-Parker and Petschek reconnection models in the context of a relativistic pair plasma. The solutions show that if the outflow velocity from the resistive region approaches the relativistic Alfven speed, the outflow density increase from Lorentz contraction allows a much faster inflow and thus a faster rate of magnetic energy dissipation than in the nonrelativistic regime. We briefly suggest applications of this result.
77 citations
76 citations
TL;DR: In this paper, the principle of electron acceleration by relativistic electron plasma waves driven by the optical mixing of laser light in a plasma was demonstrated, which corresponds to an effective accelerating electric field gradient of approximately 1.7 GeV/m.
Abstract: Experimental results are presented to demonstrate the principle of electron acceleration by relativistic electron plasma waves driven by the optical mixing of laser light in a plasma. Electrons injected at 12.5 MeV have been accelerated to 29.0 MeV over a plasma length of approximately 1 cm. This corresponds to an effective accelerating electric field gradient of approximately 1.7 GeV/m.
49 citations
TL;DR: In this paper, the authors derived the KdV equation for one-dimensional ion acoustic solitons in a plasma consisting of finite temperature drifting ions and nonrifting electrons.
Abstract: Propagation of ion acoustic solitons in a plasma consisting of finite temperature drifting ions and nondrifting electrons has been studied. It is shown that in addition to the electron inertia and weak relativistic effects, the ion temperature also modifies the soliton behavior. By including the finite ion temperature, limit for the ion drift velocity u0 for which the ion acoustic solitons are possible, is obtained. The solitons can exist for vTe≤u0≤‖u0 max‖, where vTe is the electron thermal velocity and u0 max is the maximum value of the ion drift velocity. The maximum value of this velocity is decided by the ion temperature. Under the limiting conditions, the Korteweg–deVries (KdV) equation is derived for one‐dimensional ion acoustic soliton. Expressions are obtained for the soliton phase velocity, peak soliton amplitude, soliton width, and the soliton energy. The present results correspond to those of the previous investigations under appropriate plasma conditions.
49 citations
TL;DR: In this article, the existence conditions for relativistic nonlinear Langmuir and ion-acoustic waves depend on the relativism effect, the particular energy, and the ion mass to electron mass ratio.
Abstract: Large amplitude Langmuir and ion‐acoustic waves in a weakly relativistic two‐fluid plasma are analyzed by the pseudopotential method. The existence conditions for relativistic nonlinear Langmuir waves depend on the relativistic effect, the particular energy, and the ion mass to electron mass ratio. The allowable range of the normalized potential depends on the relativistic effect. It is shown that the Mach number has the significant effect for the formation of relativistic nonlinear ion‐acoustic waves rather than the ratio of the ion‐acoustic velocity to the velocity of light. The allowable range of the normalized potential depends on the Mach number. The present investigation predicts new findings of relativistic nonlinear Langmuir and ion‐acoustic waves in plasmas in which high‐speed electrons and ions coexist.
34 citations
TL;DR: In this article, the effect of ion temperature on the conditions for existence of solitary waves in a relativistic plasma is studied using Sagdeev's pseudopotential approach.
Abstract: Effect of ion temperature on the conditions for existence of solitary waves in a relativistic plasma is studied using Sagdeev’s pseudopotential approach. It is shown that the ion temperature puts a restriction on the values of V, the soliton velocity. It is also shown that for small amplitude and cold ions, the present results agree with the existing published results. Numerical solutions of the equation of motion derived from the pseudopotential are obtained to see the effect of ion temperature on the width and amplitude of the ion‐acoustic solitary waves.
32 citations
TL;DR: In this paper, the propagation in a plasma of a high-intensity electromagnetic wave inducing both relativistic mass increase and ponderomotive expulsion of electrons is analyzed via two-dimensional simulations.
Abstract: The propagation in a plasma of a high‐intensity electromagnetic wave inducing both relativistic mass increase and ponderomotive expulsion of electrons is analyzed via two‐dimensional simulations. The time/space evolution of the wave is modeled by an axisymmetric scalar wave equation in which the plasma frequency is an instantaneous and local function of the wave energy; the incident irradiance is assumed to be constant in time. The specific features of relativistic focusing are first discussed. The ponderomotive effect enforces the focusing process by expelling the plasma electrons, creating density bumps and sharp density gradient on the edge of the light beam; the nonlinear focusing is faster and stronger confirming the paraxial/Gaussian beam core analysis presented in Part I [Phys. Fluids B 5, 3539 (1993)]. In contrast to Part I, the light is guided in a sharp‐edged density channel. The influence of the radial density inhomogeneity is then examined by using both convex (basin shape) and concave (bump shape) profiles. The self‐focusing threshold power is increased for concave profiles. For convex profiles, the natural refraction helps the self‐focusing observation but weakens the light‐guiding trend previously observed. Finally, new features characterizing wave self‐focusing, such as self‐steepening and light reflection, are shown.
31 citations
TL;DR: In this article, the results from three-dimensional electromagnetic particle simulations of an electron-positron plasma with a relativistic electron beam (γ=2) are presented.
Abstract: Results from three‐dimensional electromagnetic particle simulations of an electron–positron plasma with a relativistic electron beam (γ=2) are presented. As part of the initial conditions, a poloidal magnetic field is specified, consistent with the current carried by the beam electrons. The beam undergoes pinching oscillations due to the pressure imbalance. A transverse two‐stream instability is excited with large helical perturbations. In the process, background electrons and positrons are heated and accelerated up to relativistic energy levels. Only background electrons are accelerated farther along the z direction due the synergetic effects by both the damped transverse mode and the accompanying electrostatic waves caused by the breakdown of the helical perturbations.
TL;DR: In this article, the nonlinear evaluation of the electromagnetic waves under the condition of extreme rotation of the plasma of a rotating neutron star is studied. And the behavior of the solitons and pulsar radiation is discussed.
Abstract: The nonlinear evaluation of the electromagnetic waves under the condition of extreme rotation of the plasma is studied. Solitons are found to generate in the electron–positron plasma of a rotating neutron star. The behavior of the solitons and pulsar radiation is discussed.
TL;DR: In this article, the beating between two colinear Nd−YLF and Nd•YAG lasers in a homogeneous plasma generates intense relativistic plasma waves associated with a high longitudinal electric field of the order of 1 GV/m.
Abstract: The beating between two colinear Nd‐YLF and Nd‐YAG lasers in a homogeneous plasma generates intense relativistic plasma waves associated with a high longitudinal electric field of the order of 1 GV/m. It is shown that these electron waves couple with ion waves in the regime of modulational instability. Electric field amplitude and saturation time obtained by Thomson scattering are in agreement with theoretical predictions taking this mechanism into account.
TL;DR: In this paper, it was shown that the longitudinal dispersion relation in warm isotropic Maxwellian plasmas has two real roots with superluminal phase speed below a characteristic wave number kc determined by the plasma frequency and the plasma temperature.
Abstract: Using the relativistic Vlasov equation and the appropriate Maxwell–Boltzmann–Juttner distribution for the unperturbed plasma thermal equilibrium state, it is demonstrated that the longitudinal dispersion relation in warm isotropic Maxwellian plasmas has two real roots with superluminal phase speed below a characteristic wave number kc that is determined by the plasma frequency and the plasma temperature. The superluminal oscillations undergo no Landau damping. The relativistically correct analysis leads to markedly different results than previous nonrelativistic work which incorrectly yielded a nonzero imaginary part of the roots for all phase speeds.
TL;DR: In this paper, a fluid model is used to study the effects of background plasma in an electromagnetic pumped free-electron laser with an axial guide field, and the growth rate is formulated for the Raman regime.
Abstract: A fluid model is used to study the effects of background plasma in an electromagnetically pumped free‐electron laser with an axial guide field. The dispersion relation is derived, and the growth rate is formulated for the Raman regime. Numerical calculations are also carried out for both fast electromagnetic wave and whistler wigglers propagating opposite to the relativistic electron beam. In the case of a fast wave wiggler, the background plasma can enhance the growth rate considerably, and a much larger growth rate can be obtained around cyclotron resonance ωi∼Ω0, where ωi is the angular frequency of pump wave, and Ω0 represents the cyclotron frequency of the background plasma electrons. However, in the case of a whistler wiggler, the growth rate decreases rapidly as the plasma density increases, and a considerable decrease also occurs when ωi is near Ω0.
TL;DR: In this paper, an explanation for cyclotron emission induced by fast ions in tokamak plasmas is given for the emission observed at low harmonics in deuterium-deuterium experiments in the Joint European Torus [e.g., Phys. Rev. 60, 33].
Abstract: An explanation, supported by numerical simulations and analytical theory, is given for the harmonic cyclotron emission induced by fast ions in tokamak plasmas—in particular, for the emission observed at low harmonics in deuterium–deuterium and deuterium–tritium experiments in the Joint European Torus [e.g., Phys. Rev. Lett. 60, 33 (1988)]. It is shown that the first proton harmonic, whose field energy amplitude scales as the 0.84 power of the proton density, is one of the highest spectral peaks, whereas the first alpha harmonic is weak. The relative spectral amplitudes of different harmonics are compared. The results are consistent with the experimental observations. The simulations verify that the instabilities are caused by a weak relativistic mass effect. Simulation also shows that a nonuniform magnetic field leads to no appreciable change in the growth rate and saturation amplitude of the waves.
Journal Article•
TL;DR: In this article, the first detection of linearly polarized radio emission of the starburst galaxy M 82 at λλ6.2 and 3.6 cm is reported, and a rotation measure analysis allows the delineation of the magnetic field structure in the synchrotron halo.
Abstract: The first detection of linearly polarized radio emission of the starburst galaxy M 82 at λλ6.2 and 3.6 cm is reported. A rotation measure analysis allows the delineation of the magnetic field structure in the synchrotron halo. Also, our polarization images at these 2 wavelengths are sensitive to magneto-ionic material at the lowest density levels. The overall appearance of the magnetic field orientation strongly suggests a connection of the field lines with the streaming motions of the synchrotron emitting plasma, i.e. the magnetic field is controlled by the motion of the relativistic plasma and is convected into the M 82 halo. In particular, the northern halo exhibits a poloidal field structure, in agreement with earlier results
TL;DR: In this paper, the acceleration and heating of a relativistic electron beam induced by nonlinear Landau damping of intense electromagnetic waves in a plasma are investigated theoretically based on kinetic wave equations and momentum-space diffusion equations derived from relativistically Vlasov-Maxwell equations.
Abstract: Acceleration and heating of a relativistic electron beam induced by nonlinear Landau damping of intense electromagnetic waves in a plasma are investigated theoretically based on kinetic wave equations and momentum‐space diffusion equations derived from relativistic Vlasov–Maxwell equations. Two electromagnetic waves excite nonresonantly a beat‐wave driven relativistic electron plasma wave with a phase velocity near the speed of light [vp=c(1−γ−2p)1/2, γp=ω/ωpe]. This wave interacts nonlinearly with the electron beam and accelerates effectively it to a highly relativistic energy γpmec2. When the beat‐wave frequency equals the electron plasma frequency, the beam acceleration and the beat‐wave energy density become maximum, and they are equal to those by stimulated Raman scattering.
01 Jul 1994
TL;DR: In this paper, the pair production optical depth in relativistically expanding sources for more general cases, including shells of finite thickness and arbitrary opening angle, was investigated and the new limits on required velocity for given beaming angles and thickness will place realistic constraints on gamma-ray burst source models.
Abstract: Four bright gamma‐ray bursts detected by BATSE have also been detected at higher energies by EGRET. All are consistent with power‐law spectra extending to energies as high as, in the case of GRB930131, 1 GeV. The optical depth to photon‐photon pair production in these sources is extremely large for distances more than a few pc away if the radiation is emitted isotropically in the observer’s frame. While it has been shown that the pair production optical depth can be dramatically reduced if the source is moving with a relativistic bulk Lorentz factor Γ, calculations have been limited to cases of a beam with opening angle 1/Γ. The beaming angles required for optically thin sources are so small for Galactic halo or cosmological distances that the implied number of non‐repeating sources is unreasonably high. Spherical expansion has also been considered but only in the case of an infinitely thin shell. We have investigated the pair production optical depth in relativistically expanding sources for more general cases, including shells of finite thickness and arbitrary opening angle. The new limits on required velocity for given beaming angles and thickness will place realistic constraints on gamma‐ray burst source models.
TL;DR: In this paper, the permittivity tensor of a non-uniform medium is calculated for the collective curvature radiation from relativistic plasma placed in the strong curvilinear magnetic field.
Abstract: In the frame of ray optics it is shown how to calculate the permittivity tensor of a non-uniform medium. This tensor describes correctly the resonances between particles and electromagnetic waves. The resonances in the inhomogeneous media take into account not only the radiations existing in the uniform media (Cherenkov and cyclotron radiations) but also the bremsstrahlung and transition radiation which are due to the media inhomogeneity. We consider the collective curvature radiation from the relativistic plasma placed in the strong curvilinear magnetic field.
TL;DR: In this paper, the influence of relativistic effect on the propagation of a modified electron acoustic double layer and a small-amplitude rarefactive (MEA) soliton is investigated.
Abstract: Considering an unmagnetized plasma consisting of relativistic drifting electrons and nondrifting thermal ions and by using reductive perturbation method, a usual Korteweg–de Vries (KdV) equation and a generalized form of KdV equation are derived. It is found that while the former governs the dynamics of a small‐amplitude rarefactive modified electron acoustic (MEA) soliton, the latter governs the dynamics of a weak compressive modified electron acoustic double layer. The influences of relativistic effect on the propagation of such a soliton and double layer are examined. The relevance of this investigation to space plasma is pointed out.
TL;DR: Observed total erosion rates are in agreement with the theoretical inductive and magnetic erosion rates when they are summed and were enhanced when the beam radius was larger than the channel.
Abstract: A relativistic electron beam has propagated 91 m in a laser-ionized plasma channel across applied magnetic fields much larger than the geomagnetic field. Beam currents ranged from 0.3 to 1.0 kA and transverse magnetic fields from 0.1 to 4.0 G. Beam degradation in the form of a shortening of the current pulse (erosion) was observed. The two erosion processes were inductive and magnetic erosion. Observed total erosion rates are in agreement with the theoretical inductive and magnetic erosion rates when they are summed. Magnetic erosion was enhanced when the beam radius was larger than the channel.
Journal Article•
TL;DR: In this article, a self-consistent nonlinear theory of resistive wall instability was developed for a relativistic electron beam propagating through a grounded cylindrical resistive tube.
Abstract: A self‐consistent nonlinear theory of resistive‐wall instability is developed for a relativistic electron beam propagating through a grounded cylindrical resistive tube. The theory is based on the assumption that the frequency of the resistive‐wall instability is lower than the cutoff frequency of the waveguide. The theory is concentrated on study of the beam current modulation directly related to the resistive‐wall klystron, in which a relativistic electron beam is modulated at the first cavity and propagates downstream through the resistive wall. Because of the self‐excitation of the space charge waves by the resistive‐wall instability, a highly nonlinear current modulation of the electron beam is accomplished as the beam propagates downstream. A partial integrodifferential equation is obtained in terms of the initial energy modulation (e), the self‐field effects (h), and the resistive‐wall effects (κ). Analytically investigating the partial integrodifferential equation, a scaling law of the propagation...
TL;DR: In this article, a Pierce-type dispersion relation is derived for the interaction of an intense relativistic electron beam with a cylindrical slow-wave structure of arbitrary corrugation depth.
Abstract: A Pierce‐type dispersion relation is derived for the interaction of an intense relativistic electron beam with a cylindrical slow‐wave structure of arbitrary corrugation depth. It is shown that near a resonance, the Pierce parameter can be expressed in terms of the vacuum dispersion function and the beam current. The dispersion relation is valid in both the low‐current (Compton) regime and the high‐current (Raman) regime. The dispersion characteristics of the interaction, such as the linear instability growth rate and bandwidth, are analyzed for both regimes.
TL;DR: In this article, a class of exact one dimensional solutions for modulated light pulses coupled to electron plasma waves in a relativistic cold plasma is discussed, and numerical results for isolated envelope solitons propagating close to the velocity of light and the nonlinear relationship between their group velocity, amplitude and frequency are investigated.
Abstract: We discuss a class of exact one dimensional solutions for modulated light pulses coupled to electron plasma waves in a relativistic cold plasma and which are of great interest from the point of view of particle and photon accelerators. Numerical results are presented for isolated envelope solitons propagating close to the velocity of light and the nonlinear relationship between their group velocity, amplitude and frequency are investigated.
TL;DR: In this paper, the effect of the relativistic mass shift on the cyclotron frequency, which plays an important role in the electron cycloton range of frequencies, was not taken into account, and the object of this work is to remedy this omission.
Abstract: In a recent article Cairns et al. [Phys. Fluids B 3, 2953 (1991)] gave a method for the derivation of full wave equations describing propagation through a cyclotron resonance in an inhomogeneous plasma. The simplicity of this method compares favorably with previous derivations, and the damping resulting from the variation in the magnetic field across a Larmor orbit, described by Lashmore‐Davies and Dendy [Phys. Fluids B 1, 1565 (1989)], is included. The effect of the relativistic mass shift on the cyclotron frequency, which plays an important role in the electron cyclotron range of frequencies, was not taken into account, however, and the object of the present work is to remedy this omission. It is shown how equations, valid in the weakly relativistic regime, may be obtained in a rather straightforward way. Results obtained by a number of earlier workers are recovered and can be extended.
TL;DR: In this paper, a detailed study of the surface representing the X mode for perpendicular propagation is made, with special attention given to the connection between this mode and Gross-Bernstein modes, and non-transcendental approximations to the relativistic refractive indices for X and O modes can be given.
Abstract: The dispersion of electron cyclotron waves in a weakly relativistic Maxwellian plasma is investigated. It is shown that the apparently very complicated picture of the coupling of the extraordinary (X) mode to Bernstein waves can be accounted for in a simple way by considering the refractive indices as Riemann-like surfaces in the Clemmow-Mullaly-Allis (CMA) parameter space, ( omega p2/ omega 2, omega c/ omega ), and by introducing a few topological concepts from the analysis of complex functions. A detailed study is made of the surface representing the X mode for perpendicular propagation, with special attention given to the connection between this mode and Gross-Bernstein modes. For perpendicular propagation non-transcendental approximations to the relativistic refractive indices for X and O modes can be given. We show that these approximations are good up to approximately 25 keV and, at frequencies up to the second harmonic of the electron cyclotron frequency, the X mode approximation also accounts correctly for the connection of the X mode to Bernstein modes. The accuracy and the numerical efficiency of the approximations make them well suited for routine calculations for millimetre wave applications in fusion plasmas, including the analysis of X mode and O mode reflectometry.
Patent•
07 Mar 1994
TL;DR: In this article, a device that frequency upshifts an impinging electromagnetic wave, facilitating signal pulse compression, consisting of a semiconductor block or waveguide containing an optically induced relativistic plasma wave which interacts with an applied or self generated electromagnetic signal, is described.
Abstract: A device that frequency up-shifts an impinging electromagnetic wave, facilitating signal pulse compression, consisting of a semiconductor block or waveguide containing an optically induced relativistic plasma wave which interacts with an applied or self generated electromagnetic signal.
TL;DR: In this paper, the dispersion relation of the diocotron instability is derived and used to investigate stability properties for a broad range of system parameters including the ratio a/d of the beam thickness (2a) to the conductor gap (2d) and the charge neutralization f.
Abstract: Properties of the diocotron instability in a relativistic sheet electron beam propagating through a rectangular conducting wall are investigated within the framework of a macroscopic cold fluid model. The electron beam is assumed to be partially neutralized by the positive immobile ions with the fractional charge neutralization f. The eigenvalue equation is obtained for low‐frequency perturbations in standing waves. The dispersion relation of the diocotron instability is derived and used to investigate stability properties for a broad range of system parameters including the ratio a/d of the beam thickness (2a) to the conductor gap (2d) and the charge neutralization f. The dispersion relation indicates that the system is stabilized by increasing the neutralization f to 1/γ2b, where γb is the characteristic value of the beam relativistic factor. It is also shown that the diocotron perturbations are completely stabilized by increasing the beam thickness to more than one‐half the conductor gap (i.e., a/d≳0.5...