摘要:

During the 1969 General Assembly of URSI at Ottawa, Canada, Commission III (Ionosphere) of URSI accepted a recommendation to cosponsor a symposium entitled, ‘Waves and Resonances in Plasmas.’ The symposium should have carefully controlled attendance and be organized in cooperation with URSI Commissions IV, VI, and VII and with the International Union on Pure and Applied Physics (IUPAP). On invitation of the Canadian URSI Committee this symposium was held from July 5 through 9 at St. John's, Newfoundl

ISSN:0048-6604    

DOI:10.1029/RS007i008p00769

年代:1972

数据来源: WILEY

摘要:

The literature on the subject is reviewed under the headings: anisotropic (cold) electron plasma, isotropic (warm) electron plasma, loop antennas, resonance rectification, and ion effects. Though the gap between theory and experiment has narrowed for most of these topics, understanding is still unsatisfactory at lower frequencies where ion motion cannot be neglected.

ISSN:0048-6604    

DOI:10.1029/RS007i008p00771

年代:1972

数据来源: WILEY

摘要:

A feature of the session on the behavior of antennas in a plasma as a function of frequency of excitation was the variety of antenna configurations which was being investigated by various research groups.The emphasis by the Groupe de Recherches Ionosphériques du Centre National d'Etudes de Télécommunications (France) was on quadrupole probes.L. R. O. StoreyandJ.‐M. Chasseriauxreported on theoretical studies of plasma probes based on the mutual electrical coupling between pairs of dipole antennas. Two types of antennas were analysed, Hertzian dipoles which are short compared with the Debye‐length and double‐sphere dipoles which are long compared with the Debye‐length. In both cases the complete probe is formed by two such antennas separated by a distance much larger than a Debye‐length. The mode of operation of these quadrupole probes can be either active (by driving a current in one dipole and measuring the open circuit potential difference induced on the other) or passive (by measuring the cross‐spectrum of the fluctuating potential differences induced on the two dipoles by the plasma microfield). The quadrupole probes can be applied to the measurement of plasma resonant frequencies, collision frequencies, and the velocity of motion with respect

ISSN:0048-6604    

DOI:10.1029/RS007i008p00777

年代:1972

数据来源: WILEY

摘要:

Ionograms recorded with ionospheric sounders aboard rockets and satellites show signals (resonances) which can persist from a fraction of a millisecond to many milliseconds after the termination of the transmitted pulse. Many of the characteristics of the resonances at the plasma frequency ƒN, the upper‐hybrid frequency ƒT, the harmonic gyrofrequenciesnƒB, wheren≥ 2, and the maximum frequencies of the Bernstein modes ƒQncan be explained by propagating electrostatic waves. At frequencies near ƒN, ƒT, andnƒB, electrostatic waves of slightly different frequencies generated by the transmitted pulse propagate in the ionospheric plasma, become reflected at distances up to several hundred meters away from the satellite, and return to the satellite, producing a continuous receiver response following the transmitted pulse. The resonance observed at the gyrofrequency ƒBis not yet understood. Nonlinear properties of the receiving system and/or the plasma can result in resonances observed at the sum and difference frequencies of the principal resonances. Other resoncance phenomena are als

ISSN:0048-6604    

DOI:10.1029/RS007i008p00779

年代:1972

数据来源: WILEY

摘要:

In summarizing the discussions, the following statements appeared well established:At the plasma frequency, ƒN. The waves responsible for resonance signals are electrostatic in character. Their propagation vector k is directed nearly parallel to the magnetic field. These waves with frequency slightly greater than the plasma frequency do not exist in cold plasma theory, while in kinetic theory they appear inside the resonance cone

ISSN:0048-6604    

DOI:10.1029/RS007i008p00791

年代:1972

数据来源: WILEY

摘要:

Three papers were presented in this session, two on plasma resonances and one about Bernstein‐mode electrostatic waves.M. P. Bachynski and B. W. Gibbs(RCA Laboratories, Montreal, Canada) gave the results of their experiment which concerns electrostatic resonances excited in a layer of isotropic plasma by means of plane transverse electromagnetic waves incident from free space. The angle of incidence was small, i.e., θ = 0° ∼ 12°. Incident waves are polarized, circularly and linearly, and have a fixed frequency, 9.2 GHz. The incident power density was of the order of 0.1 mw cm−2. The thickness of the plasma slab was 1.56 free‐space wave lengths. Two electric dipoles were used as receiving antennas, one totally immersed in the plasma and the other placed outside the plasma. The immersed dipole was oriented normal to the plasma‐slab boundary and consequently nearly longitudinal to the incident wave. Strong electric fields were observed in the regions under conditions in which the frequency of the incident wave equaled the plasma frequency, and the electric vector of the incident field was in the plane of incidence. These strong fields seem to be longitudinal electrostatic fields, since only weak electric fields of longitudinal direction were observed if the incident electric field was perpendicular to the plane

ISSN:0048-6604    

DOI:10.1029/RS007i008p00795

年代:1972

数据来源: WILEY

摘要:

Although there is still only an incomplete understanding of plasma turbulence, knowledge has increased rapidly during the past few years. For weak turbulence, theory and experiment agree on the nature and strength of the interactions that occur. For strong turbulence, there is no general theory, but for some cases we have experimentally confirmed phenomenological laws which enable one to make quantitative estimates of the turbulent effects.

ISSN:0048-6604    

DOI:10.1029/RS007i008p00799

年代:1972

数据来源: WILEY

摘要:

R. J. Forrest(University College, London) examined the relation existing between various theories of helical propagation along a weakly ionized plasma column in an axial magnetic field. He showed that these particular theories are limiting cases of a general theory which includes both the effects of ion inertia and the influence of the magnetic field on the ions. The theory uses the first two fluid equations for the perturbed quantities of a warm plasma, i.e., the first two moments of the Boltzmann equation. For simplicity the model used is a planar one in which the perturbed densities and velocities for electrons and ions are introduced together with an electrostatic potential.

ISSN:0048-6604    

DOI:10.1029/RS007i008p00809

年代:1972

数据来源: WILEY

摘要:

Recent observations of both naturally occurring and triggered VLF emissions (a few KHz) made on the ground, aboard rockets, and aboard satellites are discussed. Although reference is made to auroral‐zone emissions, attention is concentrated on midlatitude discrete emissions such as chorus. FollowingBrice[1964] andKennel and Petschek[1966], the signals are interpreted as arising from the transverse resonance (or cyclotron) instability of magnetospheric plasma in the equatorial plane in the vicinity of the plasmapause. The energy of the gyroresonant electrons is estimated; the precipitation of these energetic electrons from the radiation belts is a consequence of the interactio

ISSN:0048-6604    

DOI:10.1029/RS007i008p00811

年代:1972

数据来源: WILEY

摘要:

In addition to a review on whistler mode propagation and VLF emissions, the introductory talk byM. J. Rycroft(University of Southampton, England) covered several recent topics, three of which were mostly discussed: (a) recent results of a ray tracing to be compared withWalter and Angerami's[1969] andScarabucci's[1970] computations, (b) effect of thermal anisotropy on the real part of the refractive index, hence on raytracing, especially in plasmas with β = 1, (c) simultaneous rocket observation of electron flux (energies higher than 45 kev) and whistler‐mode noise intensity.The rest of this session was mainly devoted to generation mechanisms of VLF emissions; a few other topics such as an electrostatic instability in the magnetosphere were also includ

ISSN:0048-6604    

DOI:10.1029/RS007i008p00831

年代:1972

数据来源: WILEY