ISSN:0048-6604    

DOI:10.1029/RS012i006p00859

年代:1977

数据来源: WILEY

摘要:

The results of 15 years of plasma resonance observations from rocket‐ and satellite‐borne topside sounders are summarized. The major resonances are observed at the electron plasma frequency ƒN, the electron cyclotron frequency ƒH, the upper hybrid frequency ƒT= (ƒ2N+ƒ2H)1/2, the harmonics 2ƒTandnƒHwithn>1, and two series of resonances that appear betweennƒH∶ the ƒQnresonances observed above ƒT(at the maximum frequency of the Bernstein modes) and the ƒDnresonances observed below ƒT(called the diffuse resonances). Most of the resonances can be interpreted in terms of the reception of longitudinal plasma waves stimulated by the sounder pulse. In some cases these waves, which travel with low group velocity (of the order of the electron thermal velocity or less) are received after being reflected in the nearby medium (within a distance of several kilometers). The reflections are due to the extreme sensitivity of the dispersion curves near the resonant frequencies to small changes in electron density (for the ƒNand ƒTresonances) or to small changes in magnetic field strength (for the lower‐ordernƒHresonances). In other cases (ƒQnresonances and the higher‐ordernƒHresonances) the signal reception is due to the matching of a component of the wave group velocity to the satellite velocity rather than to a wave reflection process. The ƒDnresonances involve a sounder‐stimulated electron temperature anisotropy leading to the Harris instability of the Bernstein modes and a nonlinear coupling between these wave‐modes. Since the interpretation of all of the resonances depends on warm plasma theory, the observations can be used to obtain the electron temperatureT⊥andT∥(corresponding to electron motions perpendicular and parallel to the ambient magnetic field direction, respectively) as well as the electron density and the magnetic field intensity. These measurements pertain to a large volume (hundreds of meters to kilometers) around the antenna and thus are not seriously affected by spacecraft/plasma interactions. The results of the investigations of artificially stimulated plasma waves by sounder pulses have been applied to the interpretation of naturally occurring wave phenomena such as the (n+1/2)ƒHmagnetospheric VLF emissions, the terrestrial kilometric radiation, and the Jovian decametric radiation. Among the major unexplained plasma resonance phenomena are the resonances observed at ƒHand 2ƒT, and the numerous ion effects associated with the electron plasma resonances. The advent of the Space Shuttle with subsatellites will enable active‐controlled experiments to be conducted with highly flexible radio‐frequency instrumentation in order to investigate problems of interest to many geophysical and astrophysical phenomena such as wave mode coupling and the evolution of nonli

ISSN:0048-6604    

DOI:10.1029/RS012i006p00861

年代:1977

数据来源: WILEY

摘要:

The various plasma resonance phenomena observed in the ionosphere as relaxation signals near the characteristic frequencies ƒN, ƒT(plasma and upper hybrid frequencies), andnƒH(electron gyrofrequency harmonics) have been correctly interpreted as oblique echoes. However, the ƒHcase is not yet understood. The EIDI 3 relaxation sounding rocket experiment has provided original results regarding the plasma resonances. These results provide grounds to approach the ƒHproblem. Indeed, the spectral features of the ƒHresonance signal look like pure sine‐wave ones; their frequency location is found to be very close to the gyrofrequency deduced from the earth's magnetic field model (relative frequency shift of the order of 10−4). The duration of the ƒHresonances is very short and their amplitude level very weak in the EIDI 3 ionospheric flight conditions. Moreover, a well‐defined dependence of this level on the orientation of the dipole antenna with respect to the earth's magnetic field has been pointed out, as well as an increase of the signal level when the antenna length is doubled. To interpret theoretically these experimental results, a brief review is made of the various modes of principal waves propagating close to ƒH. Their frequency range, their wave vector orientation, and the EM field polarization are examined with respect to the corresponding experimental features in order to discard the disagreeing kinds of waves. The ordinary wave mode gives good agreement with the EIDI 3 results. A first‐approach study of the interest of this mode for explaining the ƒHresonance phenomenon provides good grounds for i

ISSN:0048-6604    

DOI:10.1029/RS012i006p00879

年代:1977

数据来源: WILEY

摘要:

A diagnostic method is described in which the impulse response of a cold, lossy, magnetoplasma half space is used to infer the characteristic parameters of the plasma, namely, angular plasma frequency, electron collision frequency, and electron gyrofrequency. The method uses observations of measurable quantities from the early‐time portion of the impulse response. Using these quantities, plasma parameters can be obtained directly from a contour map. Numerical results are presented to illustrate the diagnostic techniqu

ISSN:0048-6604    

DOI:10.1029/RS012i006p00891

年代:1977

数据来源: WILEY

摘要:

A theory has been developed for the impedance of a homogeneous magnetoplasma enclosed between two specular reflecting coaxial electrodes, with a static magnetic field parallel to the electrode axes. The parallel‐plate magnetoplasma capacitor is treated as a sub‐case. Starting with the Vlasov equation, an integral equation is derived for the electric field. Solving this equation, and integrating to obtain the voltage, gives the capacitor impedance. This includes a capacitive component, and a resistive component expressing the Landau damping associated with the open orbits of electrons reflected at the electrodes. A direct numerical solution of the field integral equation has been carried out for a range of values of magnetic field, plasma density, and signal frequency. The values of impedance so obtained are compared with the predictions of macroscopic theory, and of an approximate microscopic theory in which open orbits are ignored and solutions are obtained using finite Fourier transform methods. The mathematical relations between these theories are demonstra

ISSN:0048-6604    

DOI:10.1029/RS012i006p00895

年代:1977

数据来源: WILEY

摘要:

In this paper, laboratory work dealing with the frequency characteristic of the plasma impedance of spherical and cylindrical electrode systems is reported. The influence of the ion sheath on various features of the impedance characteristic is considered as the main point of interest throughout this work. Those features are the series and parallel resonance as well as additional resonances due to the excitation of electroacoustic and cyclotron harmonic waves. The dependence of the series and parallel resonances on dc biasing leads to a method of determining the ion sheath capacityCifor a cylindrical electrode system. TheseCivalues agree fairly well with those obtained from a theoretical model for the density and potential distribution in the sheath of a cylindrical sensor aligned with a supersonic plasma flow. The amplitude of resonances due to excitation of longitudinal plasma waves (electroacoustic and cyclotron harmonic) reduces or even vanishes for sufficiently negative dc bias. Positive bias first leads to an increased amplitude up to a certain dc bias value above which, however, the amplitude decreases again due to electron absorption at the sensor surface. It is verified experimentally that large RF amplitudes exist across both the ion sheath and the plasma body in the regime of the series resonance, leading to a strong rectification effect. In this regime cyclotron harmonic waves are effectively excited, even if a strong negative dc bias voltage is applied.

ISSN:0048-6604    

DOI:10.1029/RS012i006p00921

年代:1977

数据来源: WILEY

摘要:

This paper describes a series of experiments designed to examine the antenna characteristics of probes which are used as detectors in ion‐acoustic wave experiments. Reception patterns are measured which are in qualitative agreement with theoretical predictions. The near‐field antenna pattern of the wave‐launching grid is found to be impo

ISSN:0048-6604    

DOI:10.1029/RS012i006p00935

年代:1977

数据来源: WILEY

摘要:

This three‐part paper describes linear and nonlinear plasma wave phenomena in an infinite, homogeneous, collisionless, warm magnetoplasma by means of a microscopic Lagrangian. Part 1 derives the dispersion relation for all modes of linear wave propagation. To do so, the charged particle position vectors and the fields are first expanded in terms of sinusoidal perturbations from equilibrium. The contribution to the microscopic Lagrangian, expanded to second order in the perturbations, is then averaged over space and time to remove rapidly varying terms. The Euler‐Lagrange equations, obtained from variations of the Lagrangian with respect to the amplitudes of the perturbation parameters, are the first‐order Maxwell equations and the perturbed particle trajectory. Variation with respect to the phase gives the equation of conservation of action. The Lagrangian is specialized to waves propagating nearly parallel, and exactly perpendicular, to the static magnetic field, and familiar wave dispersion relations are obtained. In Part 2, the nonlinear coupling of these waves is studied. In Part 3, both wave‐wave and wave‐particle interactions are taken int

ISSN:0048-6604    

DOI:10.1029/RS012i006p00941

年代:1977

数据来源: WILEY

摘要:

The averaged‐Lagrangian method is applied to wave‐wave interactions in an infinite, homogeneous, collisionless, warm magnetoplasma. The amplitudes of the waves are assumed to vary slowly in time and space, due to coupling between them. Euler‐Lagrange equations are obtained from the contributions to the averaged microscopic Lagrangian second and third order in perturbation, by variation with respect to the wave amplitudes. These are the coupled‐mode equations. The phase variation yields the action transfer equation. As applications of the method, coupled‐mode equations are derived in explicit forms for all possible interactions among waves propagating nearly parallel, and among those propagating exactly perpendicular, to the static magnetic field. Some of the coupling coefficients are new. Where comparisons with previous iterative analyses are possible, the advantages of the method are

ISSN:0048-6604    

DOI:10.1029/RS012i006p00953

年代:1977

数据来源: WILEY

摘要:

The averaged‐Lagrangian method is applied to nonlinear wave‐particle interactions in an infinite, homogeneous, magnetic‐field‐free plasma. The specific example of Langmuir waves is considered, and the combined effects of four‐wave interactions and wave‐particle interactions are treated. It is demonstrated how the latter lead to diffusion in velocity space, and the quasilinear diffusion equation is derived. The analysis is generalized to the random phase approximation. The paper concludes with a summary of the method as applied in Parts 1–3

ISSN:0048-6604    

DOI:10.1029/RS012i006p00965

年代:1977

数据来源: WILEY