Longitudinal Plasma Waves Research Articles

The coupled mode approach to nonlinear wave interactions and parametric instabilities

The non-linear interaction of a few coherent, weakly damped longitudinal and transverse waves in an unmagnetized plasma is considered by means of the coupled mode theory. Using the equations describing the non-linear wave interactions the threshold electric fields and initial growth rates of a number of parametric instabilities are calculated. The following four instabilities, all of which are relevant to laser fusion are considered: (i) the parametric ion-acoustic-Langmuir wave integration, (ii) the two plasmon decay, (iii) stimulated Raman scattering and (iv) stimulated Brillouin scattering. All these instabilities are driven by a large amplitude electro-magnetic wave.

Ion effects on ionospheric electron resonance phenomena

Ion effects are often observed on topside‐sounder‐stimulated electron plasma wave phenomena. A commonly observed effect is a spur, appearing after a time delay corresponding to the proton gyroperiod, attached to the low frequency side of an electron plasma resonance. The spurs are often observed on the resonances at the electron plasma frequency, fN, the harmonics nfH of the electron cyclotron frequency fH (n = 2, 3, 4, ···), and occasionally on the upper hybrid frequency (fN2 + fH2)1/2. The spurs on the fN resonance are usually quite small unless the fN resonance overlaps with an nfH resonance; very large spurs are observed during such overlap conditions. Proton spurs are only observed on the nfH resonances when the electron plasma waves associated with these resonances are susceptible to the Harris instability and when the electromagnetic z wave can be initiated by the sounder pulse. This instability is the result of a sounder‐stimulated anisotropic electron velocity distribution. The observations suggest that energy is fed into the nfH longitudinal plasma wave from the z wave by means of wave‐mode coupling.

Electron Plasma Relaxation Processes

The solution of the Vlasov equation for the longitudinal electron plasma wave is obtained by using Neumann series method. The electron relaxation process is analytically described by the superposition of expressions for electron streamings and Coulomb collisions. The currently established formula for the longitudinal plasma wave is also explained by the closed-form solution of the Vlasov equation. The expression effectively describes the detailed physical processes of the electron plasma wave relaxation both in space and time.

Stimulation of the Harris instability in the ionosphere

Satellite soundings of the topside ionosphere reveal diffuse signals on the low frequency side of nfH when nfH < fT, where n is an integer and fH and fT are the electron cyclotron and upper hybrid frequencies, respectively. They extend no further than the midway point between (n − 1)fH and nfH. The present observing conditions allow detection up to n = 10. The origin of the signals is attributed to the Harris instability of longitudinal plasma waves when T⊥/T‖ > 2n, where T⊥ and T‖ refer to the temperature corresponding to the electron motion perpendicular and parallel to the earth's magnetic field, respectively. The large anisotropies are caused by collisionless cyclotron damping of energy from the high power sounder pulse. This energy is absorbed in a region which extends radially from the antenna, a distance which is small compared with the antenna length but large compared with the antenna sheath region.

The Contribution to Nonlinear Frequency Shifts from Diffusion in Velocity Space

The resonant interaction of four longitudinal plasma waves is investigated taking into account the influence of the waves on the background distribution function. This effect gives an essential contribution to the nonlinear frequency shift. Langmuir waves in a cold plasma are considered as an example.

Theory and simulation of collisional damping of longitudinal waves in a two-dimensional plasma

The collisional damping of plasma oscillations is studied by numerical simulation techniques. The results agree with the theoretical calculation of collisional damping in a two-dimensional plasma, resolving discrepancies which had previously existed between analytic and simulation approaches to this problem.

Electron Plasma Relaxation Processes

The solution of the Vlasov equation for the longitudinal electron plasma wave is obtained by using Neumann series method. The electron relaxation process is analytically described by the superposition of expressions for electron streamings and Coulomb collisions. The currently established formula for the longitudinal plasma wave is also explained by the closed-form solution of the Vlasov equation. The expression effectively describes the detailed physical processes of the electron plasma wave relaxation both in space and time.

Instability of longitudinal cyclotron waves in a rarefied plasma having velocity dispersion of the electrons

Instability of longitudinal cyclotron waves in a rarefied plasma having velocity dispersion of the electrons

High frequency induced enhancements of the incoherent scatter spectrum at Arecibo, 2

When the ionospheric F region is illuminated with a strong O mode HF radio wave, excitations of longitudinal plasma and acoustic waves are observed by 430-MHz radar scattering. The frequency structure of the excited waves and their variability with local parameters, time, and space are described. The observations are interpreted in terms of parametric instability theory. The spectra of the observed features and the correlation of their amplitudes are shown. The upshifted and downshifted plasma lines exhibit some marked asymmetries. Absolute as well as relative amplitudes of the enhancement are presented.

Envelope Shock Waves in Interactions of Longitudinal Plasma Waves of Random Phase

Envelope Shock Waves in Interactions of Longitudinal Plasma Waves of Random Phase

Theory of a corner-driven loop antenna immersed in a warm plasma

Abstract A linearized hydrodynamic theory and potential function technique arc used to formulate the theory of a corner-driven loop antenna immersed in a warm plasma. The theory explains some of the experimental observations obtained from impedance measurement of a loop antenna on the Ariel 3 satellite. The far-zone fields and the normalized radiated power for different antenna sizes are calculated. The results suggest that much of the radiated energy is radiated in longitudinal plasma waves

Five Wave Interaction–a Possibility for Enhancement of Optical or Microwave Radiation by Nonlinear Coupling to Explosively Unstable Plasma Waves

A rigorous solution is obtained to the problem of five wave interaction in a plasma medium for the case where two of the waves are transverse electromagnetic waves, whereas the remaining three waves are longitudinal plasma or beam waves. The effects of nonlinear instability are studied in a coherent wave description. As a result enhancement of radiative waves may occur in media of interest to high power laser and present day astrophysical research.

Reception Characteristics of Monopole Antennas for Electron Plasma Waves

The radiation patterns of a longitudinal electron plasma wave excited in a warm unbounded plasma by a grid and parallel plane grids and the reception patterns for wire antennas and the grid having a grounded plate were measured experimentally. The results agreed well with theoretically predicted radiation patterns based on a fluid model description for electrons. The dependence of the received amplitude of a gridded parallel plate on the D. C. potential of the antenna was studied. The possibility of estimating the wavelength from measured amplitudes of the wire antenna and the gridded parallel plate is also discussed.

Symmetry properties in a two-stream electrostatic instability

A double stream consisting of immobile ions and mobile electrons which is partly drifting and partly stationary is considered. Certain symmetry properties of the dispersion relation of the longitudinal plasma wave having its wave vector parallel to the direction of the electron stream are discussed. These symmetry properties enable the results for a particular value of the relative number density of the streaming electrons to be deduced from the corresponding results for the same value of the relative number density for the stationary electrons.

Absorption of Light at Oblique Incidence on a Plasma Layer

Two effects are examined which may lead to enhanced absorption of light by sharply bounded plasma layers at oblique incidence. The first is a resonance absorption caused by interference of light reflected from the front and rear boundaries of the layer. The second is the linear coupling of the incident transverse wave into longitudinal plasma waves. It is thought that these effects may be useful in obtaining increased efficiency in laser heating of plasmas.

A photon rest mass and the absorption of longitudinal electric waves in interstellar space

The author treats the absorption of longitudinal electric waves in a cold plasma; upper limits for absorption in propagation from the galactic centre to the Earth are estimated.

Time of flight studies of propagating electrostatic longitudinal waves in an homogeneous plasma

Describes an experimental measurement of the time of flight of a high frequency electrostatic longitudinal sine wave burst through a hot, homogeneous and isotropic plasma. The group velocity of the pulse was measured with a good accuracy for frequencies higher than 1.2 times the plasma frequency (fp). For frequencies between fp and 1.2 fp (in this range the plasma is a high dispersive medium), and for small distances of propagation, up to 2 wavelengths the pulse maximum travels with a velocity lower than the group velocity, in good agreement with numerical calculation. For larger distances of propagation, the sine wave burst splits into 2 pulses: the first pulse seems to be due to the propagation of electron-ballistic waves, while the second one is characteristic of the principal Landau poles.

A photon rest mass and the dispersion of longitudinal electric waves in interstellar space

Treats the propagation of longitudinal electric waves in a cold plasma, which can occur if the photon has a nonzero rest mass.

Frequency shifts of ionospheric [formula omitted] resonances

The Alouette II resonances observed near the harmonics of the electron cyclotron frequency ƒ H reveal frequency shifts (relative to the nƒ H values derived from model field calculations) which can be consistently interpreted in terms of plasma wave dispersion effects superimposed on a positive offset of several kilohertz in the Alouette II sounder transmitter frequency and a negative offset of a few tens of gammas in the Earth's magnetic field ¦ B¦ (relative to the model field under quiet conditions near the magnetic equator). Plasma wave dispersion effects are observed on the 2ƒ H resonance when it is in the vicinity of the resonance observed near the upper hybrid frequency ƒ T . The 2ƒ H resonant frequency shift is positive when ƒ T < 2ƒ H and negative when ƒ T > 2ƒ H . The observed shift is more than an order of magnitude greater than that expected from a matching of the group velocity of longitudinal plasma waves propagating perpendicular to B, to the component of the satellite velocity perpendicular to B. The observations suggest that an oblique echo model may be required to give a proper interpretation of the 2ƒ H resonance. Comparing the frequency shifts observed near ƒ T with theory indicates that cyclotron damping can be ignored only when the angle between the propagation vector k and the direction perpendicular to B is less than a few degrees for the 2ƒ H wave, and less than a few tenths of a degree for the nƒ H waves with n > 2. The large positive frequency shifts previously attributed to the Alouette II ƒ H and 2ƒ H resonances can be explained by assuming a positive instrumental frequency offset. The negative offset of ¦ B¦ inferred from the plasma resonance observations is consistent with expectations based on recent OGO 3 and OGO 5 rubidium magnetometer observations at higher altitudes in the equatorial regions.

Nonlinear collisional excitation of plasma waves

The interaction between two electromagnetic waves in a current carrying electron plasma is studied. It is shown that nonlinearities in the collision term may be responsible for the excitation of longitudinal plasma waves.