RADIATION FROM A PHASED LINE SOURCE IN A MAGNETOIONIC MEDIUM

1965 ◽  
Vol 43 (9) ◽  
pp. 1636-1648
Author(s):  
H. S. Tuan ◽  
S. R. Seshadri
Keyword(s):  
Electric Current ◽  
Current Distribution ◽  
Free Space ◽  
Line Source ◽  
Propagation Constant ◽  
Electron Plasma ◽  
Radiation Characteristics ◽  
Magnetostatic Field ◽  
Phase Constant ◽  
Special Case

The radiation characteristics of a phased line source of electric current immersed in a magnetoionic medium are analyzed. The line source is assumed to be parallel to the direction of the external magnetostatic field and the phase constant for the current distribution is assumed to be given by k0/β, where k0 is the propagation constant of free space and β is a dimensionless phase parameter. In general, it is found that two modes are excited. The frequency ranges of propagation of these so-called ordinary and extraordinary modes are examined by means of a construction in the Ω2–R2 parameter space for the case [Formula: see text], where Ω = ω/ωp, R = ωc/ωp, and ω, ωp and ωc are the source, the electron plasma, and the gyromagnetic frequency respectively. The dispersion relations and the frequency spectrum are evaluated. It is found that β = 1 is a special case for which only one mode is excited.

EFFECT OF ION SHEATH ON RADIATION IN A MAGNETOIONIC MEDIUM: I. SOURCE CURRENT PARALLEL TO THE MAGNETOSTATIC FIELD

1966 ◽  
Vol 44 (7) ◽  
pp. 1401-1418
Author(s):  
S. R. Seshadri ◽  
K. L. Bhatnagar
Keyword(s):  
Point Source ◽  
Electric Current ◽  
Finite Length ◽  
Current Distribution ◽  
Radiation Resistance ◽  
Free Space ◽  
Sheath Thickness ◽  
Radiation Characteristics ◽  
Magnetostatic Field ◽  
Source Current

The radiation characteristics of an axially oriented point source of electric current and a filament of finite length with a triangular current distribution are treated for the case in which these sources are situated at the center of an infinite cylindrical column of free space and surrounded by a homogeneous, loss-free magnetoionic medium. The direction of the magnetostatic field is assumed to be parallel to the axis of the free-space column which is an idealization for the geometry of the ion sheath formed around the antenna in the ionosphere. The dependence of the radiation resistance of these sources on the frequency and the ion-sheath thickness is examined. It is found that, within the framework of the classical magnetoionic theory, the radiation resistance of even a point source of electric current remains finite for all frequencies, provided the ion-sheath effects are included. Also the radiation resistance of a finite-length filament with a triangular current distribution is found to be insensitive to the changes in the thickness of the ion sheath. This result is in conformity with the experimental observations, which indicate no data variations correlated with the changes in the thickness of the ion sheath.

Current distribution on a thin cylindrical antenna immersed in an isotropic compressible plasma

1968 ◽  
Vol 46 (8) ◽  
pp. 1013-1017 ◽  
Author(s):  
Richard L. Monroe
Keyword(s):  
Current Distribution ◽  
Integrodifferential Equation ◽  
Free Space ◽  
Plasma Frequency ◽  
Propagation Constant ◽  
Wave Number ◽  
Compressible Plasma ◽  
Cylindrical Antenna ◽  
Space Wave

An integrodifferential equation is derived for the current distribution along a thin, hollow, center-driven, cylindrical, perfectly conducting antenna immersed in an isotropic, compressible plasma. On the basis of this equation it is shown that the current distribution approaches sinusoidal form as the radius of the antenna approaches zero. The propagation constant for this current is approximately equal to the free-space wave number for most frequencies greater than the plasma frequency.

RADIATION FROM ELEMENTARY FLUID-MECHANICAL SOURCES IN AN UNBOUNDED ELECTRON PLASMA

1964 ◽  
Vol 42 (8) ◽  
pp. 1573-1586 ◽  
Author(s):  
S. R. Seshadri
Keyword(s):  
Line Source ◽  
Uniform Magnetic Field ◽  
Electron Plasma ◽  
The Other ◽  
Frequency Range ◽  
Entire Frequency Range ◽  
Fluid Flux ◽  
Radiation Characteristics ◽  
Transverse Waves ◽  
Infinite Extent

The radiation characteristics of a line source of fluid flux and a line source of force, embedded in a homogeneous electron plasma of infinite extent, are investigated for the case in which a uniform magnetic field is impressed externally throughout the medium in the direction of the source. It is found that there are two propagating modes which are strictly coupled longitudinal and transverse waves. However, one of the modes is predominantly transverse in the entire frequency range of propagation and the other is predominantly transverse in the lower, and predominantly longitudinal in the higher ranges of frequency of propagation. It is shown that the elementary fluid-mechanical sources considered in this paper radiate significant amounts of power only in the longitudinal-type waves.

Anomalous absorption of the circularly polarized electromagnetic beams near the plasma frequency in a magnetized electron plasma

2007 ◽  
Vol 73 (3) ◽  
pp. 315-330 ◽  
Author(s):  
S. R. SESHADRI
Keyword(s):  
Resonant Frequency ◽  
Plasma Frequency ◽  
Unit Length ◽  
Plane Waves ◽  
Electron Plasma ◽  
Magnetostatic Field ◽  
Power Absorption ◽  
Circularly Polarized ◽  
Focused Beams ◽  
Electromagnetic Beams

AbstractThe propagation of circularly polarized electromagnetic beams along the magnetostatic field in an electron plasma is investigated. As a consequence of a strong interaction with the medium, the beam spreads rapidly on propagation near the cutoff frequencies and the cyclotron resonant frequency of the corresponding plane waves, as well as near the plasma frequency. The power absorption for unit length near the cyclotron frequency and the plasma frequency are determined. For tightly focused beams, there is significant power absorption near the plasma frequency as compared with that at the cyclotron resonant frequency.

scholarly journals Time evolution of electric fields and currents and the generalized Ohm's law

2005 ◽  
Vol 23 (4) ◽  
pp. 1347-1354 ◽  
Author(s):  
V. M. Vasyliūnas
Keyword(s):  
Electric Field ◽  
Electric Current ◽  
Time Evolution ◽  
Time Scales ◽  
Current Density ◽  
Time Derivative ◽  
Electron Plasma ◽  
Displacement Current ◽  
Ohm’S Law ◽  
Ohm's Law

Abstract. Fundamentally, the time derivative of the electric field is given by the displacement-current term in Maxwell's generalization of Ampère's law, and the time derivative of the electric current density is given by the generalized Ohm's law. The latter is derived by summing the accelerations of all the plasma particles and can be written exactly, with no approximations, in a (relatively simple) primitive form containing no other time derivatives. When one is dealing with time scales long compared to the inverse of the electron plasma frequency and spatial scales large compared to the electron inertial length, however, the time derivative of the current density becomes negligible in comparison to the other terms in the generalized Ohm's law, which then becomes the equation that determines the electric field itself. Thus, on all scales larger than those of electron plasma oscillations, neither the time evolution of J nor that of E can be calculated directly. Instead, J is determined by B through Ampère's law and E by plasma dynamics through the generalized Ohm's law. The displacement current may still be non-negligible if the Alfvén speed is comparable to or larger than the speed of light, but it no longer determines the time evolution of E, acting instead to modify J. For theories of substorms, this implies that, on time scales appropriate to substorm expansion, there is no equation from which the time evolution of the current could be calculated, independently of ∇xB. Statements about change (disruption, diversion, wedge formation, etc.) of the electric current are merely descriptions of change in the magnetic field and are not explanations.

RADIATION FROM A LINE SOURCE IN A UNIAXIALLY ANISOTROPIC PLASMA

1963 ◽  
Vol 41 (2) ◽  
pp. 246-257 ◽  
Author(s):  
H. S. Tuan ◽  
S. R. Seshadri
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Line Source ◽  
Plasma Frequency ◽  
Angular Spectrum ◽  
Radiation Characteristics ◽  
Magnetic Current ◽  
Line Charge ◽  
Unit Path Length ◽  
Moving Line

Two problems of radiation in a magnetized, incompressible plasma are investigated. The radiation characteristics of a line source of magnetic current are studied for the case in which the external magnetic field is infinite and oriented in a direction perpendicular to that of the source. The second problem that is treated is the radiation from a uniformly moving line charge. Two cases are considered, namely: (1) when the motion of the line charge is parallel and (2) when it is perpendicular to the direction of the external magnetic field. In each case it is found that there is a Cerenkov-type radiation for frequencies less than the plasma frequency. The frequency and the angular spectrum, as well as the total energy radiated per unit path length, are determined for both cases.

scholarly journals Integrals of the equations of electrodynamics with to the electric constants of a transparent medium

1926 ◽  
Vol 113 (764) ◽  
pp. 237-253 ◽  
Keyword(s):  
Electric Current ◽  
Current Distribution ◽  
Magnetic Force ◽  
Small Radius ◽  
Transparent Medium ◽  
Electric Force ◽  
Present Communication ◽  
Magnetic Current ◽  
Magnetic Forces ◽  
Equations Of Electrodynamics

Integrals of the equations of propagation of electrical disturbances have been given by the present writer which express the electric and magnetic forces at any point outside a surface enclosing all the sources in terms of an electric current distribution and a magnetic current distribution over the surface. The result for a source at a point can be obtained by taking as the surface a sphere of very small radius with its centre at the point. This suggests that the equations representing Faraday’s laws can be written 1/V 2 ∂X/∂ t +4π i x = ∂ϒ/∂ y – ∂β/∂ z , 1/V 2 ∂X/∂ t + 4π i v =∂∝/∂ z – ∂ϒ/∂ x , 1/V 2 ∂z/∂ t – 4π i z = ∂β/∂ x – ∂∝/∂ y (1) – ∂∝/∂ t + 4π m x = ∂z/∂ y – ∂Y/∂y, – ∂β/∂t + 4π my = ∂X/∂ z – ∂Z/∂ x , – ∂ϒ/∂ t + 4π mz ∂Y/∂ x – ∂X/∂ y , (2) where X, Y, Z are the components of the electric force, α, β, γ are the components of the magnetic force, i x , i y , i z are the components of an electric current distribution, and m x , m y , m z are the components of a magnetic current distribution throughout the space. The object of the present communication is to express X, Y, Z, α, β, γ in terms of the electric current and magnetic current distributions and to apply the result to the discussion of the electric constants of a transparent medium. It is convenient to take instead of equations (1) and (2) the following equations, which include (1) and (2) as a particular case

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