Electron Density Oscillations Research Articles

A new method for accurate ionospheric electron density measurements by incoherent scatter radar

It is shown that the detectability of the plasma line in incoherent scatter radar experiments on the ionospheric plasma can be increased by factors in the range of 10–100 by chirping the transmitter frequency at a rate matching the rate of change of plasma frequency with height. The method is explained in detail, and some initial experiments carried out at the Arecibo Observatory are described. Plasma frequency versus height profiles with an accuracy better than one part in 10³ were established with 1‐s integration time per point. An example of quasi‐periodic oscillation of ionospheric electron density with a period of about 18 min is also shown. The chirped frequency observations will greatly facilitate plasma line studies of photoelectrons, allow for studies of small‐amplitude wavelike density perturbations, provide electron density profiles with high time resolution and unprecedented accuracy, make it possible to measure electron temperature independently of ion temperature, and probably allow for observations of vertical currents.

Gravity wave induced ionization layers in the night F-region over Cachoeira Paulista (22°S, 45°W)

Ionosonde observations over Cachoeira Paulista (22°S, 45°W), a low-latitude station, show distorted h(ƒ) traces in the ionograms due to passage of TIDs. The distortions of the traces, at times, take the form of an F-region bifurcated into two distinct layers. These effects are observed mostly during presunrise hours. One specific event is studied in greater detail using true height analysis of the quarter hourly ionograms. The characteristics of the electron density and height oscillations for this case are compared with the results obtained, from the simulation of the same, based on linear theory of gravity wave induced ionization perturbations. The results show that gravity wave winds of unrealistically large magnitudes are required to explain the observation. The results suggest further that the inclusion of a source of ion production in the presunrise period, perhaps, produced by precipitation of low energy (< 10 keV) electrons in the South Atlantic anomaly, together with the ionization loss process, might lead to a better agreement between the observation and the theory.

A Theory of the Onset and the Pinning of Charge Density Wave in a Quasi One-Dimensional Conductor

Two kinds of functions of the impurity are studied for the charge density wave (CDW) in a Quasi one·dimensional conductor, by considering the case of a single impurity. We formulate our problem in the self-consistent field approximation and near the transition point to the CDW state. It is pointed out that the impurity·induced Friedel oscillation of electron density as well as the symmetry-breaking effect of impurity in the usual sense governs the processes of the onset and the pinning of CDW below the transition point. They are described in terms of the effective local Fermi wavenumber and the local amplitude of CDW. Both the functions work cooperatively, S0 that the effective local Fermi wavenumber remains uniform in a range as wide as possible. Concerning the amplitude they work destructively in an important range of distance from the impurity. The distortion above the transition point is expressed by the effective local Fermi wavenumber and a localized amplitude. It is essentially a long-ranged reproduction of the Friedel oscillation, as the Friedel oscillation is the sole source of distortion.

Rearrangement effects in photoionization

The recent developments and the physical backgrounds of the random phase approximation with exchange (RPAE) method are briefly discussed. The limitations of RPAE and the main features of a more general theory that would be free of RPAE difficulties are considered. The generalizations of RPAE are discussed that permit one to take into account the rearrangement of electron shells in the course of ionization and the effects due to the decay of the vacancy created in the ionization process. The role of the two-electron-two-hole virtual excitation is examined. The possibility is discussed of the existence of large amplitude electron density oscillations in atoms.

The charge density wave and the impurity in a linear conductor

Two kinds of functions of the impurity are studied for the charge density wave in a linear conductor. It is pointed out that the impurity-induced Friedel oscillation of electron density as well as the symmetry breaking effect of impurity govern the process of the onset and the pinning of the charge density wave.

Electron density oscillations around an adatom

An analytical asymptotic expression for the induced electron density oscillations around an adatom is derived. Four different regions can be distinguished: preasymtotic, bulk asymptotic ( R −3 decay of the amplitude of the oscillations), transition (no simple inverse power law) and far asymptotic ( R −5 decay parallel to the surface, R −3 into the metal) regions.

A layer summation for electrostatic surface problems. Application to the classical cleavage energy

AbstractA rather general method is given for calculating the electrostatic potential due to a half‐infinite 2D‐lattice periodic charge distribution. Such kind of potentials arises in the Coulomb integrals of the classical cleavage energy (a contribution to the surface energy) or in calculating ionic lattice relaxation near metal surfaces. For the former quantity numerical results are presented here. It is found that the contribution due to bulk electron density oscillations must be taken into account even for simple metals to get results for the total surface energy comparable with experimental ones (rather than with experimental surface tensions). Taking into account these density oscillations the anisotropy ratios are markedly improved, too. The calculation is made for all simple metals in terms of pseudopotential theory.

Microwave measurement of plasma density fluctuation amplitudes

A microwave beam is used to detect ion-cyclotron oscillations in the 2XIIB mirror device. A model is used to estimate electron density and electric field oscillation amplitudes from measured modulation sideband intensities. Semiquantitative agreement is obtained with electrostatic probe measurements.

Satellite Generation of Electron Plasma Waves form Low Frequency Oscillations in Plasmas

Experiments demonstrating that the satellite generation of a stable electrostatic wave in the presence of an electron density oscillation in a bounded plasma and that the satellite generation of the unstable plasma wave in a modulated electron beam-plasma system are described. The spatially periodic energy transfer among the satellite modes and the primary mode is observed, which results in an enhanced damping of the stable primary mode in the former case and a decrease in a growth rate of the unstable primary mode in the latter. These results are compared with the theoretical prediction derived by expanding the wave number in terms of fluctuating plasma parameters as well as by using the coupled mode equations.

Oscillation of Conduction Electron Density near the Solute Atoms in Dilute Cu‐Fe Alloys

Oscillation of Conduction Electron Density near the Solute Atoms in Dilute Cu‐Fe Alloys

Enhanced damping of electrostatic waves due to combination scattering from density oscillation in plasmas

Experiments demonstrating the combination scattering of the electrostatic wave from the electron density oscillation in plasmas are described. The spatially periodic energy transfer among the satellite modes and the primary mode is observed, which results in an enhanced damping of the primary mode.

Suppression of Two-Stream Instability by Beam Modulation

Standing waves of longitudinal electron oscillation were observed in a beam-plasma system. By applying a density modulation to the beam, the amplitude of oscillation decreased to zero when the modulation frequency was near to those of the spontaneous oscillation. The modulation depth necessary for the oscillation to vanish was nearly proportional to the difference between the oscillation frequency and the modulation one. When the oscillation was suppressed, the oscillation having the same frequency as the modulation one was excited. These suppression and synchronization can be well explained by the assumption that the oscillation of electron density is described by the Van der Pol equation. Under this self-oscillator model the linear growth rate is evaluated and compared with the value calculated from the dispersion equation of the two-stream instability.

Quadrupole structure in the nuclear magnetic resonance of dilute aluminium-zinc alloys

Structure due to nuclear quadrupole interaction has been observed in the 27Al magnetic resonance from dilute alloys of zinc in aluminium. Analysis gives the following values for the quadrupole coupling constants at the first- and second-nearest-neighbour positions around a zinc atom: e2qQ/h = (923 ± 10)kHz and (176 ± 8)kHz with asymmetry factors η = 0.249 ± 0.010 and η = 0 respectively. The results support the existence of oscillations of conduction electron density around the zinc atoms but it is necessary to consider the departure of the screening-charge distribution from spherical symmetry. This requires some modification of theory.

Low-Frequency Oscillations in CdS Single Crystals

Low-frequency current oscillations in CdS single crystals were observed. One type of oscillations was a damped one, and the other type of oscillations was continuous and only observed under superposed infrared light which produces quenching. The retrapping rate of the free holes and the occupation probability among the traps control the free electron density oscillation.

Electron-Density Oscillations in a General Potential

Electron-Density Oscillations in a General Potential

Langmuir Probe Method for a Plasma Having Small Amplitude Oscillations

Langmuir probe characteristics for a plasma having oscillations of space potential, electron density and electron temperature are discussed in detail. The method to derive amplitudes of oscillation as well as values of d.c. component of them in the case of the ideal plane probe are introduced. In order to get informations about oscillating components, “method of constant current probe” developed by Barnes and Eros is applied with some extention. The newly developed method to determine the amplitude of oscillation of the electron temperature seems to be useful because of its improved accuracy.

Long Range Electron Density Oscillations at Non-zero Temperatures

The form of the electron density surrounding a spherically symmetric defect in a Fermi gas at non-zero temperature is calculated. At large distances and moderate temperatures the density decay contains a factor (πkFkT /2EF) csch(πkT/EF) kFr and reduces at zero temperature to the well-known inverse cube dependence of amplitude on distance.

Theory of Plasma Resonance

Starting from the Boltzmann transport equation, a formula is derived for the rate of change of electron density in a gas plasma. With its aid a study is made of the oscillations of electron density (about the steady state value) in a discharge confined between parallel plates. The oscillations are described in terms of a set of normal modes characteristic of the plasma under study. An expression is obtained for the impedance of the discharge as a function of frequency: for the one case calculated in detail, this formula gives a resonance in power absorption at a frequency of 0.7 of the plasma resonance frequency corresponding to the central electron density.