Measurements of broadband electrostatic wave emIssons in conjunction with particle distributions in the earth's magnetosphere, have provided motivation for a number of studies of waves in plasmas with two electron components. One such wave-the electron-acoustic wave-arises when the two electron components have widely disparate temperatures (Watanabe & Taniuti 1977), and has a characteristic frequency that lies between the ion and electron plasma frequencies. Because of this broadband nature and because it is predominantly electrostatic, it provides a likely candidate for the explanation of the electrostatic component of "cusp auroral hiss" observed in the dayside polar cusp at between 2 and 4 earth radii as well as the broadband electrostatic noise (BEN) observed in the dayside polar regions and in the geomagnetic tail. The electron-acoustic wave and its properties provide the subjects for much of the investigation undertaken in this thesis. The thesis is divided into two parts. Part I is concerned with certain aspects of the linear theory of the electron-acoustic wave and is based on a kinetic description of the plasma. The dispersion relation for plane electrostatic waves obtained via linearisation of the Vlasov-Poisson system is studied in detail using analytical and numerical/geometrical techniques, and conditions under which the electron-acoustic wave arises are expounded. This work represents an extension of earlier works on Langmuir waves (Dell, Gledhill & Hellberg 1987) and the electron-acoustic wave (Gary & Tokar 1985). The effects of electron drifts and magnetization are investigated. These result, respectively, in a destabilization of the electron-acoustic wave and a modification of the dispersive properties. In this plasma configuration the model more closely replicates the conditions to be found in the terrestrial polar regions. We extend the parameter regimes considered in earlier works (Tokar &Gary 1984) and in addition, identify another electron sound branch related to the electron-cyclotron wave/instability. Effects of ion-beam destabilization of the electron-acoustic wave are also investigated briefly with a view to explaining BEN in the geomagnetic tail and also to provide a comparison with the electron-driven instability. In part II the nonlinear electron-acoustic wave is studied by employing a warm hydrodynamic model of the plasma components. We first consider weak nonlinearity and employ the asymptotic reductive perturbation technique of Washimi &Taniuti (1966) to render the hydrodynamical equations in the form of simpler evolutionary equations describing weakly-nonlinear electron-acoustic waves. These equations admit solitary-wave or soliton solutions which are studied in detail. Wherever possible we have justified our small amplitude results with full numerical integration of the original hydrodynamical equations. In so doing we extended the range of validity of our results to arbitrary wave amplitudes and also find some interesting features not directly predicted by the small amplitude wave equations. In this respect we were able to determine the important role played by the cool- to-hot electron temperature ratio for soliton existence. This important effect is in accordance with linear theory where the electron temperature ratio is found to be critical for electron-acoustic wave existence. The effects of magnetization on electron-acoustic soliton propagation is examined. We found that the magnetized electron-acoustic solitons are governed by a Korteweg-de Vries-Zakharov-Kusnetsov equation. In addition, it is shown that in very strong magnetic fields ion magnetization can become important yielding significant changes in the soliton characteristics. Multi-dimensional electron-acoustic solitons, which have greater stability than their plane counterparts, are also briefly discussed. Employing a weakly-relativistic hydrodynamic model of the plasma, the effect of a cool, relativistic electron beam on such soliton parameters as width, amplitude and speed is studied in detail. Both small- and large amplitude solitons are considered. The arbitrary-amplitude theory of Baboolal et al. (1988) is generalised to include relativistic streaming as well as relativistic thermal effects. The importance of the cool electron (beam)to- hot electron temperature in conjunction with the beam speed is pointed out. Finally, we derive a modified Korteweg-de Vries (mKdV) equation in an attempt to establish whether electron-acoustic double layers are admitted by our fluid model. Although double layers formally appear as stationary solutions to the mKdV equation, the parameter values required are prohibitive. This is borne out by the full fluid theory where no double layer solutions are found. / Thesis (Ph.D.)-University of Natal, Durban, 1991.

Thesis (Ph. D.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains v, 152 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

This thesis presents results on the description of plasma waves in terms of wavepackets. The wave field is decomposed into a distribution of wavepackets in a space of position, wavevector, time, and frequency. A complex structure joining each pair of Fourier conjugate variables into a single complex coordinate allows the efficient derivation of equations of motion for the phase space distribution by exploiting its analytic properties. The Wick symbol calculus, a mathematical tool generalizing many convenient properties of the Fourier transform to a local setting, is used to derive new exact phase space equations which maintain full information on the phase of the waves and include effects nonlocal in phase space such as harmonic generation. A general purpose asymptotic expansion of the Wick symbol product formula is used to treat dispersion, refraction, photon acceleration, and ponderomotive forces. Examples studied include the nonlinear Schrödinger equation, mode conversion, and the Vlasov equation. The structure of partially coherent wave fields is understood in terms of zeros in the phase space distribution caused by dislocations in its complex phase which are shown to be correlated with the field entropy. Simulations of plasma heating by crossing electron beams are understood by representing the resulting plasma waves in phase space. The local coherence properties of the beam driven Langmuir waves are studied numerically.

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Plasmas confined by a dipole magnetic field exhibit interchange and entropy mode turbulence causing bursty intermittent transport of particles and energy [1]. On the Collisionless Terrella Experiment (CTX), this turbulence is dominated by low-frequency, long-wavelength modes with amplitudes and phases that vary chaotically in time [2]. We present a new paradigm for characterizing this turbulence by measuring the time-evolution of the fluctuation power spectrum and the instantaneous bispectrum using the continuous wavelet transform [3, 4] and computing the statistical properties of turbulent wave kinetics. We observe that both the fluctuation power and the energy transfer by three-wave coupling, or bispectrum, between these fluctuations can be intermittent. When antenna are used to actively launch waves into the turbulence, the intermittency of the driven waves decreases, while the intermittency of other waves increases. Similarly, application of active feedback [5] to amplify the turbulence decreases the intermittency of the wave energy, while suppressing feedback increases this intermittency. Measurements based on this new paradigm show that the transfer of wave energy to larger and smaller scales in a turbulent plasma is not steady but occurs in short and intense bursts, analogous to the better-known short bursts of particle transport in magnetized plasma.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19508号 / 理博第4168号 / 新制||理||1599(附属図書館) / 32544 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 田口 聡, 教授 家森 俊彦, 教授 余田 成男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Electron Bernstein waves are a mode of oscillation in a plasma, thought a candidate for providing radiofrequency heating and non-inductive current drive in spherical tokamaks. Previous studies of these modes have relied on neglecting or simplifying the contribution made by relativistic effects. This work presents fully relativistic numerical results that show the mode's dispersion relation for a wide range of parameters. Relativistic effects are shown to shift the location of the resonance as in previous studies, but the effects beyond this are shown to matter only in high temperature (10-20keV) plasmas. At these higher temperatures however, the fully relativistic model differs markedly. The assumption that the mode is electrostatic is looked at, and found to be inadequate for describing fully the electron Bernstein modes dispersion relation. Simple estimates that neglect toroidal effects show current drive efficiency is expected to be an order of magnitude higher than that for conventional electron cyclotron current drive using the O or X modes. It is shown for a number of model tokamaks that heating the center of the plasma and driving current using EBWs is impossible launching from the outside due to strong damping of the wave at higher cyclotron harmonics. Results from a code based on a more complicated semi-analytic model of current drive, that includes toroidal effects and calculates the average current drive over the magnetic surface, confirm the higher expected current drive efficiency, and the code is shown to give good agreement with a Fokker-Planck code. The higher values of perpendicular refractive index associated with the EBWs are shown to mitigate the deleterious effects of trapping on current drive efficiency to a small extent. The details of the magnetic field are found to be unimportant to the calculation beyond determing where the wave is absorbed. The codes written to produce these results are outlined before each set of results. The last of these is considerably faster than conventional Fokker-Planck codes and a useful tool in studying electron cyclotron current drive in the future.

This work deals with the linear analysis of plasma waves, especially with the methods of solution of a hot plasma dispersion relation. There are cited some results achieved in the space plasma research and mapped current numerical methods of their analysis. Besides, this work introduces a new numeric procedure, computer code PDRS (Plasma Dispersion Relation Solver), which allows finding solution of a dispersion function of a cold or hot plasma with general distribution function. It also demonstrates the usage of the PDRS methods on real examples of waves in space plasma based on the spacecraft Cluster measurement.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1978. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 110-111. / B.S.