Wave coupling across a shock wave in a viscous plasma
Electron-acoustic, ion-acoustic and electromagnetic plane waves coupling at shock front in two fluid ionized viscous plasma
Francis, S. H.↗
SEARCH · Engineering Papers
Results for “ion-acoustic waves”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Long wavelength irregularities in the equatorial electrojet
The radar interferometer technique is used at Jicamarca to study in detail irregularities with wavelengths of a few kilometers generated in the unstable equatorial electrojet plasma during strong type 1 conditions. In-situ rocket observations of the same instability process are discussed in a companion paper. These large scale primary waves travel essentially horizontally and have large amplitudes. The vertical electron drift velocities driven by the horizontal wave electric fields reach or exceed the ion-acoustic velocity even though the horizontal phase velocity of the wave is considerably smaller. A straightforward extension to the long wavelength regime of the usual linear theory of the electrojet instability explains this and several other observed features of these dominant primary waves.
Kudeki, E.↗
Microscale instabilities in stream interaction regions
The microstructure of solar wind stream interaction regions is considered theoretically with emphasis on the role of several electrostatic kinetic instabilities which may be important within the stream interface and the compression region. Inside of 1 AU, the interface is likely to be stable against the electrostatic streaming instabilities considered. Between 1 and 2 AU, the interface will excite the magnetized ion-ion instability. The compression region is also found to be unstable beyond 1 AU where the modified two-stream instability, beam-cyclotron instability, and ion-acoustic instability are important in determining the structure of the compressive pulses as they evolve into forward and reverse shocks. It is concluded that the modified two-stream instability and beam-cyclotron instability predominately play a role in heating the electrons to the threshold for the ion-acoustic instability. Various electrostatic plasma waves, ranging in frequency from the lower-hybrid to harmonics of the electron cyclotron frequency, would be produced by these instabilities. Their signature should also be seen by high time resolution measurements of the temperature of the various plasma species.
Eviatar, A.↗
Parametric interaction and spatial collapse of beam-driven Langmuir waves in the solar wind
Observations are presented of the parametric decay and spatial collapse of Langmuir waves driven by an electron beam streaming into the solar wind from the Jovian bow shock. Long wavelength Langmuir waves upstream of the bow shock are effectively converted into short wavelength waves no longer in resonance with the beam. The conversion is shown to be the result of a nonlinear interaction involving the beam-driven pump, a sideband emission, and a low level of ion-acoustic turbulence. The beam-driven Langmuir wave emission breaks up into a complex sideband structure with both positive and negative Doppler shifts. In some cases, the sideband emission consists of isolated wave packets with very short duration bursts, which are very intense and are thought to consist of envelope solitons which have collapsed to spatial scales of only a few Debye lengths.
Gurnett, D. A.↗
Role of ion acoustic instability in magnetic reconnection
We report on a first-principles numerical study of magnetic reconnection in plasmas with different initial ion-to-electron temperature ratios. In cases where this ratio is significantly below unity, we observe intense wave activity in the diffusion region, driven by the ion-acoustic instability. Our analysis shows that the dominant macroscopic effect of this instability is to drive substantial ion heating. In contrast to earlier studies reporting significant anomalous resistivity, we find that anomalous contributions due to the ion-acoustic instability are minimal. These results shed light on the dynamical impact of this instability on reconnection processes, offering new insights into the fundamental physics governing collisionless reconnection.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Progress and problems in the theory of type III solar radio emission
The experimental and theoretical status of type III solar radio emission is considered in detail. Very recent developments which are relevant to the underlying plasma physics are emphasized. In particular, the identity of the submegahertz emissions as fundamental, or second harmonic, the degree of correlation between emissivities, electron streams, and plasma (Langmuir) waves, paradoxes concerned with the time-ordering of these phenomena, and the role of background density irregularities and ion-acoustic turbulence in the solar wind, are discussed. From the theoretical point of view, the current picture of the underlying Langmuir turbulence, including such effects as the interaction between Langmuir waves and stream electrons, induced scatter off ions, and strong turbulence effects such as modulational instability and soliton collapse, is discussed.
Goldman, M. V.↗
Magnetic field reconnection in a collisionless plasma
A reasonably consistent model of steady-state magnetic-field-line reconnection in a collisionless plasma is constructed by incorporating ion-acoustic anomalous resistance into the hydromagnetic flow in the vicinity of the x-type neutral line. The Petschek-Vasyliunas (1975) reconnection theory is applied, and properties of the ion-acoustic instability are reviewed for the case of comparable ion and electron temperatures. Nonlinear saturation of the instability is examined, the saturation wave intensity is determined as a function of electron drift speed and electron/ion temperature ratio, and the computed wave intensities are used to estimate the steady electric field in the neutral region. Ion-acoustic anomalous resistance is shown to limit the electron drift speed to slightly above the marginally stable value. A model for the resistive-diffusion region is constructed which incorporates the properties of ion-acoustic anomalous resistance, and an approximate solution for the external flow region is matched to the resistive-region solution. It is found that the two solutions are sensibly matched only for a restricted range of upstream plasma parameters. Limitations and possible extensions of the model are discussed.
Coroniti, F. V.↗
Anomalous resistivity resulting from electrostatic ion cyclotron turbulence
The paper considers the generation of electrostatic ion cyclotron turbulence in an isothermal isotropic magnetized plasma where the drift velocity is below that of the ion-acoustic threshold. The saturated turbulence spectrum is found to be that which results from anomalous nonlinear wave damping related to stochastic ion-orbit diffusion in configuration space. An expression is obtained for the collective electrical resistivity resulting from current-driven electrostatic ion cyclotron turbulence.
Ionson, J. A.↗
Nature and the nonlinear evolution of electrostatic waves associated with the AMPTE solar wind releases
The nonlinear evolution of the electrostatic waves observed during the AMPTE (Active Magnetosphere Particle Tracer Explorers) solar wind releases is investigated. Previous linear studies indicate two distinct sets of instabilities may be responsible for the generation. One set consists of ion-acoustic type instabilities which are insensitive to the presence of a background magnetic field, while the other group corresponds to the modified two stream instabilities and requires the solar wind flow to be across the ambient magnetic field. To establish which set of instabilities is more viable a detailed linear Vlasov theory has been conducted by numerically solving the full electromagnetic dispersion relation. In addition both the plasma wave as well as the magnetic field measurements by the IRM (Ion Release Module) spacecraft were used to correlate the frequency and the power of the observed waves with the magnitude and the direction of the solar wind magnetic field. The results of these analyses indicate that the ion-acoustic type instabilities have growth rates that are an order of magnitude or more larger than those of the modified two stream instabilities. Results show that both the solar wind protons and the released ions may be heated and accelerated in the directions oblique to the solar wind flow velocity.
Omidi, N.↗
On the marginally stable saturation spectrum of unstable type I equatorial electrojet irregularities
Formulation of a self-consistent convective nonlinear theory of type I irregularities in the equatorial electrojet. It is found that a combination of three mechanisms - convective amplification, quasi-linear polarization electric field reduction, and nonlinear particle orbit diffusion damping - accounts for radar backscatter observations of a ubiquitous marginally stable (or 'constant ion-acoustic Doppler shift') saturation spectrum better than any of the three mechanisms treated separately. In particular, no spatially homogeneous theory without wave refraction can account for the observations. Wave refraction alone or with quasi-linear polarization electric field reduction is also inadequate. Wave refraction, quasi-linear polarization reduction, and particle orbit diffusion theory appear to account for type I observations at radar elevation angles less than 60 deg. Vertical type I backscatter cannot be explained without modifying the present laminar electrojet model.
Lee, K.↗
Turbulence in electrostatic ion-acoustic shocks
Three types of collisionless electrostatic ion-acoustic shocks are investigated using the University of California, Los Angeles, double plasma device: (1) laminar shocks; (2) small amplitude turbulent shocks in which the turbulence is confined to be upstream of the shock potential jump; and (3) large amplitude turbulent shocks in which the wave turbulence occurs throughout the shock transition. The wave turbulence is generated by ions which are reflected from the shock potential; linear theory spatial growth increments agree with experimental values. The experimental relationship between the shock Mach number and the shock potential is shown to be inconsistent with theoretical shock models which assume that the electrons are isothermal. Theoretical calculations which assume a trapped electron equation of a state and a turbulently flattened velocity distribution function for the reflected ions yields a Mach number vs potential relationship in agreement with experiment.
Means, R. W.↗
Microwave signature of thick-target electron beams in solar flares
The steady-state behavior of a flux of nonthermal electrons injected into a fully ionized thick target is examined. Owing to the (inverse square) energy dependence of the Coulomb collisional cross section, it is found that injected electron distributions that are monotonically decreasing functions of electron energy develop at finite depths into distributions that have 'humps' in velocity space; the electron energy corresponding to the hump correlates with the overlying particle column density to the target. This results in a two-stream unstable situation. The distribution is constantly being relaxed by quasi-linear relaxation and re-created by collisions; in this way a steady nonthermal level of Langmuir plasma waves is created, and these waves in turn produce microwave plasma radiation with a typical flux of 3 x 10 to the -16th erg/sq cm-sec. This flux can be enhanced by a factor of up to 100 by a high level of low-frequency (such as ion-acoustic) turbulence, which prevents quasi-linear relaxation for a sufficient fraction of the path length.
Emslie, A. G.↗
A laboratory investigation of the high-frequency Farley-Buneman instability
A laboratory investigation of the high-frequency Farley-Buneman instability is described. The instability was studied theoretically and is predicted to occur in the low E region of the ionosphere when the E/B drift velocity of the electrons relative to the ions is several times Cs, the ion-acoustic speed. In the experiments, an increase of the electric field well above the Lee threshold merely enhances the general power level of the fluctuations but does not effect appreciably their spectral shape. The observed frequency spectra fall-off in all cases very rapidly with increasing frequency, with a spectral shape of the type P(f) alpha 1f to the 3.5 power. This result has negative implications for a recently proposed mechanism of anomalous wave electron heating in the lower E region of the ionosphere.
Kustom, B.↗
Theory and simulations of broadband electrostatic noise in the geomagnetic tail
The excitation mechanism for broadband electrostatic noise (BEN) and the effects of BEN particles in the geomagnetic tail are examined using the linear analysis theory and particle simulations. The linear theory for electrostatic instabilities is discussed. The plasma sheet particle population is simulated using counter-streaming cold ion beams, and warm ions and electrons. The ion-ion instability, ion-acoustic mode, and the electrostatic ion cyclotron harmonic waves are studied. The velocity distributions, electric field intensity, and electron plasma waves for the plasma sheet boundary layer are evaluated. The frequency wave spectrum and particle distributions are computed and analyzed. The conditions for the two simulations, which differ only in beam ion drift speed, are described; it is observed that in the first simulation the dominate modes propagate parallel to the magnetic field and in the second simulation the propagation modes are oblique. The simulation data reveal that when beam temperature is smaller than plasma sheet temperature ion-acoustic and ion-ion instabilities grow to large amplitudes heating both electrons and ions. The data are compared to ISEE-1 observations and good correlation is obtained.
Ashour-Abdalla, M.↗
Nonlinear evolution, propagation, electron-trapping, and damping effects of ion-acoustic solitons using fully kinetic PIC simulations
We investigate ion acoustic solitary waves (solitons) of varying amplitudes in a one-dimensional plasma using fully kinetic particle-in-cell simulations. The initial soliton conditions are based on the Korteweg–de Vries (KdV) equation, treating ions as a cold species and electrons with finite temperature. Our findings reveal that KdV solitons evolve nonlinearly to a saturated state at higher amplitude, deviating from KdV predictions for ion density and electric potential, and from the Boltzmann relation for electron density. At this saturated state, the KdV model cannot accurately describe the soliton behavior. For small amplitudes, Sagdeev's model describes the saturated state, but not the soliton width; for larger amplitudes, it models the width accurately, but not the amplitude. These discrepancies arise from assuming a Boltzmann relation for electron density, while electron trapping creates non-Boltzmann densities—a deviation that increases with soliton amplitude. Additionally, we observe that the soliton amplitude oscillates roughly at the electron bounce frequency. The soliton is better described by Schamel's electron density formulation and a modified KdV equation incorporating electron trapping. The soliton velocity matches best with predictions from Sagdeev's and Schamel's models. Moreover, the soliton speed–amplitude relationship differs from existing theoretical predictions. Finally, we find minimal ion and electron Landau damping effects.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Ion-acoustic instability of a two-temperature, collisional, fully-ionized plasma.
From a perturbation analysis of the fluid equations for a homogeneous unmagnetized plasma, it is shown that long wavelength ion waves are unstable when the electron temperature exceeds the ion temperature. Thus, the temperature difference can drive a resistive-type ion wave instability in a plasma which on a collisionless basis is stable. The additional destabilizing effect of a current is also investigated.
Rognlien, T. D.↗
A study of plasma expansion phenomena in laboratory generated plasma wakes - Preliminary results
The plasma expansion into the wake of a large rectangular plate immersed in a single-ion, collisionless, streaming plasma has been investigated in the laboratory. Several characteristics of the process involved in 'plasma expansion into vacuum' that have been predicted theoretically were observed, including the creation and motion of a rarefaction wave disturbance; the creation and motion of an expansion front; and the acceleration of ions into the wake at speeds above the ion-acoustic speed. The expansion was limited to early times; i.e., a few ion plasma periods, by the combination of plasma drift speed and vacuum chamber size. This prevented detailed comparison with self-similar theory, but results are in good agreement with numerical simulations and other laboratory experiments for the early time expansion. The conclusion is that the plasma expansion process is the dominant wake filling mechanism in the near wake of a body, whose potential is approximately the plasma space potential.
Wright, K. H., Jr.↗
Ion-acoustic instabilities driven by an ion velocity ring
A ring distribution of ions in velocity space can generate electrostatic waves which propagate predominantly along an ambient magnetic field at frequencies comparable with the ion plasma frequency. A dispersion equation which accounts for these waves is presented, and solved analytically and numerically. It was found that ion-acoustic-like waves are excited in a plasma even if the electron temperature is comparable with the in temperature under the assumption of an anisotropic ion distribution.
Akimoto, K.↗