Plasma Electromagnetics-Admittance of the Infinite Cylindrical Antenna Immersed in a Lossy, Compressible Plasma.pdf (original) (raw)
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An analysis of the current on an infinite cylindrical dipole antenna which is excited across a circumferential gap of nonzero thickness and immersed in a lossy, compressible magnetoplasma with its axis parallel to the static magnetic field is described. Some numerical results are presented for the antenna admittance for the sheathless case, where the uniform magnetoplasma is in contact with the antenna surface. The admittance values are obtained from a numerical integration of the Fourier integral for the antenna current, and are given for plasma parameter values typical of the E region of the ionosphere.
A numerical investigation of the admittance of an infinite, circular cylindrical antenna excited at a circumferential gap of nonzero thickness, and immersed in a lossy incompressible magnetoplasma with the antenna parallel to the static magnetic field is described. A concentric free-space layer (the vacuum sheath) which separates the antenna from the external uniform plasma is included in the analysis to approximate the positive ion sheath which may form about a body at floating potential in a warm plasma. The numerical results for the antenna admittance show that: (1) in the absence of a sheath, a sharp admittance maximum is found at the electron cyclotron frequency, with the maximum more pronounced when the plasma frequency exceeds the cyclotron frequency than for the converse case; (2) the vacuum sheath shifts upward in frequency and reduces in amplitude the admittance maximum which occurs for the sheathless case at the cyclotron frequency; (3) a kink, or minimum in the admittance is found at the plasma frequency.
Plasma Electromagnetics-Characteristic Waves on an Infinite Cylindrical Antenna in a Plasma Medium'
An analysis of the current on an infinite cylindrical dipole antenna immersed in a lossy plasma medium that may, in the general case. be both compressible and anisotropic, is discussed. The antenna current, for the isotropic, incompressible plasma with no sheath present is evanescent along the antenna axis for frequencies (f) less than the electron plasma frequency (fp ). When f> f," the current is axially propagating with a wave number whose real component K., is given by Kso where KE0 is the free-space electromagnetic wave number. Addition of a static magnetic field parallel to the antenna axis opens up a region of propagating antenna current below the electron cyclotron frequency (A) with Kn. = KE0 V1-4-11(j2 -42 ), so that the region of evanescent current is reduced to f,, < f < fr = A further decrease in the region of evanescent current behavior to approximately (fh +9f,)/10 <f <f, is effected by plasma compressibility or a vacuum sheath. At the same time, the value of K; in the latter case may exceed KE0 by two or three orders of magnitude in the range (AA-Pa c f< j; so that the electrical wavelength of a finite antenna in the plasma would be a more sensitive function of frequency than for the free-space medium.
The Finite Tubular Antenna in a Warm Plasma
Radio Science, 1968
A cylindrical dipole antenna, immersed in a warm homogeneous and isotropic plasma and driven at the center by a delta-function voltage generator, is treated as a boundary value problem. The current on the antenna is determined and found to consist of two parts: a slowly varying component that varies like the current on an antenna in a cold medium, and an oscillating component. The spatial periodicity of• the oscillatory component is of the same order as that of the surface waves launched on an infinite tube containing and surrounded by warm plasma. If the antenna is driven well above the plasma frequency, the oscillatory portion of the current is negligible, while if it is driven at slightly above the plasma frequency, the oscillatory portion of current is dominant. It is found that a radiation resistance calcula_tion made by using a current distribution valid only for an antenna in a cold environment can be incorrect when applied to an antenna in a warm plasma.
Plasma sheath structures around a radio frequency antenna
Journal of Geophysical Research, 2008
A one-dimensional particle-in-cell (PIC) simulation code is developed to investigate plasma sheath structures around a high-voltage transmitting antenna in the inner magnetosphere. We consider an electrically short dipole antenna assumed to be bare and perfectly conducting. The oscillation frequency of the antenna current is chosen to be well below the electron plasma frequency but higher than the ion plasma frequency. The magnetic field effects are neglected in the present simulations. Simulations are conducted for the cases without and with ion dynamics. In both cases, there is an initial period, about one-fourth of an oscillation cycle, of antenna charging because of attraction of electrons to the antenna and the formation of an ion plasma sheath around the antenna. With the ion dynamics neglected, the antenna is charged completely negatively so that no more electrons in the plasma can reach the antenna after the formation of the sheath. When the ion dynamics are included, the electrons impulsively impinge upon the antenna while the ions reach the antenna in a continuous manner. In such a case, the antenna charge density and electric field have a brief excursion of slightly positive values during which there is an electron sheath. The electron and ion currents collected by the antenna are weak and balance each other over each oscillation cycle. The sheath-plasma boundary is a transition layer with fine structures in electron density, charge density, and electric field distributions. The sheath radius oscillates at the antenna current frequency. The calculated antenna reactance is improved from the theoretical value by 10%, demonstrating the advantage of including the plasma sheath effects self-consistently using the PIC simulations. The sheath tends to shield the electric field from penetrating into the plasma. There is, however, leakage of an electric field component with significant amplitude into the plasma, implying the applicability of the high-voltage antennas in whistler wave transmission in the inner magnetosphere.
Plasma Electromagnetics-Results from a Swept-Frequency, Ionospheric Impedance Probe.pdf
Experimental results are presented for the impedance of a rocket-borne dipole antenna immersed in the ionospheric plasma. The dependence of several interesting impedance artifacts upon the antenna position relative to the Earth's magnetic field and rocket motion through the ionospheric plasma are shown. Possible evidence for plasma compressibility is provided by an impedance discontinuity occurring consistently at approximately twice the electron cyclotron frequency and a frequency shifted cyclotron-resonance impedance minimum.