Beam-plasma interaction in randomly inhomogeneous plasmas and statistical properties of small-amplitude Langmuir waves in the solar wind and electron foreshock (original) (raw)
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Plasma density fluctuations in solar corona and Langmuir wave generation by an electron beam
Astronomy & Astrophysics, 2001
The problem of beam propagation in a plasma with small scale and low intensity inhomogeneitiesis investigated. It is shown that the electron beam propagates in a plasma as a beam-plasma structure andis a source of Langmuir waves. The plasma inhomogeneity changes the spatial distribution of the waves. Thespatial distribution of the waves is fully determined by the distribution of plasma inhomogeneities. The possibleapplications to the theory of radio emission associated with electron beams are discussed.
Journal of Geophysical Research: Space Physics, 2017
Langmuir amplitude modulation in association with type III radio bursts is a well-known phenomenon since the beginning of space observations. It is commonly attributed to the superposition of beam-excited Langmuir waves and their backscattered counterparts as a result of parametric decay. The dilemma, however, is the discrepancy between fast beam relaxation and long-lasting Langmuir wave activity. Instead of starting with an unstable electron beam, our focus in this paper is on the nonlinear response of Langmuir oscillations that are driven after beam stabilization by the still persisting current of the (stable) two-electron plasma. The velocity distribution function of the second population forms a plateau (index h) with a point at which f h v ∼ 0 associated with weak damping over a more or less extended wave number range k. As shown by particle-in-cell simulations, this so-called plateau plasma drives primarily Langmuir oscillations at the plasma frequency (e) with k = 0 over long times without remarkable change of the distribution function. These Langmuir oscillations act as a pump wave for parametric decay by which an electron-acoustic wave slightly below e and a counterstreaming ion-acoustic wave are generated. Both high-frequency waves have nearly the same amplitude, which is given by the product of plateau density and velocity. Beating of these two wave types leads to pronounced Langmuir amplitude modulation, in reasonable agreement with solar wind and terrestrial foreshock observations made by the Wind spacecraft.
Advances in Space Research, 1997
Recent theoretical work on foreshock Langmuir wave generation has emphasized the importance of proximity to the solar wind/electron foreshock boundary. Waves generated near the boundary decouple quickly from the tenuous beam and evolve by wave-wave interactions; deeper in the foreshock, the effect of damping and beam bunching should be more pronounced. We compare observed electron distributions and wave intensities to study the effect of various cutoff distributions. The distribution of wave amplitudes is consistent with stochastic growth theory which implies that the distribution function should only be observed as unstable very infrequently. 01997 COSPAR. Published by Elsevier Science Ltd.
Waveforms of Langmuir turbulence in inhomogeneous solar wind plasmas
Journal of Geophysical Research: Space Physics, 2014
Modulated Langmuir waveforms have been observed by several spacecraft in various regions of the heliosphere, such as the solar wind, the electron foreshock, the magnetotail, or the auroral ionosphere. Many observations revealed the bursty nature of these waves, which appear to be highly modulated, localized, and clumped into spikes with peak amplitudes typically 3 orders of magnitude above the mean. The paper presents Langmuir waveforms calculated using a Hamiltonian model describing self-consistently the resonant interaction of an electron beam with Langmuir wave packets in a plasma with random density fluctuations. These waveforms, obtained for different profiles of density fluctuations and ranges of parameters relevant to solar type III electron beams and plasmas measured at 1 AU, are presented in the form they would appear if recorded by a satellite moving in the solar wind. Comparison with recent measurements by the STEREO and WIND satellites shows that their characteristic features are very similar to the observations.
Annales Geophysicae, 2004
We present the statistics of Langmuir wave amplitudes in the Earth's foreshock using Cluster Wideband Data (WBD) Plasma Wave Receiver electric field waveforms from spacecraft 2, 3 and 4 on 26 March 2002. The largest amplitude Langmuir waves were observed by Cluster near the boundary between the foreshock and solar wind, in agreement with earlier studies. The characteristics of the waves were similar for all three spacecraft, suggesting that variations in foreshock structure must occur on scales greater than the 50-100 km spacecraft separations. The electric field amplitude probability distributions constructed using waveforms from the Cluster WBD Plasma Wave Receiver generally followed the log-normal statistics predicted by stochastic growth theory for the event studied. Comparison with WBD receiver data from 17 February 2002, when spacecraft 4 was set in a special manual gain mode, suggests nonoptimal auto-ranging of the instrument may have had some influence on the statistics.
Nonlinear interactions of langmuir waves in a weakly inhomogeneous plasma
Journal of Applied Mechanics and Technical Physics, 1972
Kinetic equations for the scattering of the waves of the one-dimenslonal spectrum by plasma particles are obtained for a weakly inhomogeneous plasma. The equation for the evolution of the spectrum of the short waves [k 2 > (me/mi) De-2] trapped in the inhomogeneities of the plasma density differs significantly from the kinetic equation for the waves in a homogeneous plasma. The problem of localization on the spectrum of the Langmuir waves in regions near the minima of the plasma density is also considered. A solution of the kinetic equation for the waves, which describes this process, is obtained. A number of papers [1-3] have dealt with the influence of a weak inhomogeneity of plasma density on the effective interaction of particles and waves in a plasma. The presence of an inhomogeneity in real experiments may greatly distort the dynamics of such processes in comparison with the model conditions of the homogeneous plasma. Thus, in [1] it is indicated that an appreciable change takes place in the spectrum of the Langmuir waves generated by an electron beam as a result of the existence of a weak inhomogeneity in the plasma density in the beam propagation direction. The method of [1] can be applied to an analysis of the nonlinear interaction of Langmuir waves of a one-dimensional spectrum. Following [1], we consider a one-dimensional inhomogeneity of the plasma density in the form n (x) = no (x0) + an (z) (0.1)
Nonlinear Evolution of Beam-Plasma Instability in Inhomogeneous Medium
The Astrophysical Journal, 2010
The problem of electron-beam propagation in inhomogeneous solar wind is intimately related to the solar type II and/or type III radio bursts. Many scientists have addressed this issue in the past by means of quasi-linear theory, but in order to fully characterize the nonlinear dynamics, one must employ weak-turbulence theory. Available numerical solutions of the weak-turbulence theory either rely on only one nonlinear process (either decay or scattering), or when both nonlinear terms are included, the inhomogeneity effect is generally ignored. The present paper reports the full solution of weak-turbulence theory that includes both decay and scattering processes, and also incorporating the effects of density gradient. It is found that the quasi-linear effect sufficiently accounts for the primary Langmuir waves, but to properly characterize the back-scattered Langmuir wave, which is important for eventual radiation generation, it is found that both nonlinear decay and scattering processes make comparable contributions. Such a finding may be important in the quantitative analysis of the plasma emission process with application to solar type II and/or type III radio bursts.
On the amplitude of intense Langmuir waves in the terrestrial electron foreshock
Journal of Geophysical Research, 1997
Waveforms of large-amplitude Langmuir oscillations were recorded by the Wind spacecraft in the Earth's upstream electron foreshock region. We present some statistics of the waveforms and discuss them in the context of various saturation mechanisms. In particular, it is found that the value of Epeak/Erm s is not large, as previously suggested, and that the largest-amplitude Langmuir waveforms are generally somewhat sinusoidal and lack structure on small spatial scales. The measured probability distribution of electric field amplitude and dimensionless energy suggest that some stochastic process may play a role in wave generation. The values of dimensionless energy needed to arrest Langmuir wave collapse occur with very small probability and the value of Epeak/Erm s for large fields suggests that, statistically, Langmuir wave collapse is not an important process in the terrestrial foreshock. Introduction Despite many years of observational and theoretical work, the generation and saturation of Langmuir waves in the solar wind upstream of the Earth's bow shock remains an interesting, even controversial, problem. The flux of accelerated solar wind electrons upstream from the bow shock is thought to generate a beam-like "cutoff" distribution due to time-of-flight effects [Filbert and Kellogg, 1979]; this should exist irrespective of, and in addition to, other processes which may generate beams near the foreshock-solar wind boundary (e.g., fast Fermi processes [Wu, 1984; Leroy and Mangehey, 1984]). This beam is then unstable to Langmuir waves as well as beam modes [e.g., Cairns, 1989]. The fast Fermi process, which operates most efficiently at quasiperpendicular shocks, has been shown to generate an energetic ring beam [Krauss-Vatban and Burgess, 1991] and ring beams can generate Langmuir waves as well as electromagnetic radiation [Kainer and MacDowall, 1996]. There are various proposed saturation mechanisms for the Langmuir waves. In the strong turbulence scenario, the electric field pressure of the wave modifies the ambient plasma, thereby changing the dispersion properties of the wave. This definition of strong turbulence incorporates such effects as the modulational Copyright 1997 by the American Geophysical Union. Paper number 97JA00938. 014g-O227/97/97JA-00938509.00 instability, reactive parametric decay instability, and Langmuir soliton collapse. Goldman [1984], Melrose [1991], and Robinson [1997] offer good reviews of these Zakharov, V. E., Collapse of Langmuir waves, Soy. Phys. JETP, 35, 908, 1972.
Turbulence and Microprocesses in Inhomogeneous Solar Wind Plasmas
Fluids, 2019
The random density fluctuations observed in the solar wind plasma crucially influence on the Langmuir wave turbulence generated by energetic electron beams ejected during solar bursts. Those are powerful phenomena consisting of a chain of successive processes leading ultimately to strong electromagnetic emissions. The small-scale processes governing the interactions between the waves, the beams and the inhomogeneous plasmas need to be studied to explain such macroscopic phenomena. Moreover, the complexity induced by the plasma irregularities requires to find new approaches and modelling. Therefore theoretical and numerical tools were built to describe the Langmuir wave turbulence and the beam’s dynamics in inhomogeneous plasmas, in the form of a self-consistent Hamiltonian model including a fluid description for the plasma and a kinetic approach for the beam. On this basis, numerical simulations were performed in order to shed light on the impact of the density fluctuations on the b...
Czechoslovak Journal of Physics, 2006
The propagation of a cloud of hot electrons in a plasma and generation of Langmuir waves are investigated using numerical simulation of quasilinear equations. It is shown that for an initially stable hot electron beam instability proceeds as a result of advection and generated Langmuir waves are completely reabsorbed by next arriving slower electrons and reabsorption is maximal near the upper velocity boundary of the plateau at the electron distribution function. However, for unstable injection of the beam a part of waves fails to be reabsorbed and remains at the site of injection. The level and spatial extent of these waves depend on the slope of the initial distribution function. For multi-beam injection the number of regions at the site of injection with high level of waves, depends on the temperature of the beams and their separation in the velocity space.