Impedance of a short dipole in a compressible plasma

Abstract

Th e fi e ld of a c ylindri ca l dipo le an te nna in a comp ress ible, isotro pi c, loss y plasma is re prese nt ed by th e fi e ld of a cy lindri ca l c urre nt s hee t imm e rsed in th e plasma . Th e a nt e nna is s ho rt compared to a fr ee s pace wav ele ngth a nd fo r thi s re aso n a tri a ng ul ar curre nt di s tributi o n is ass um ed. A fo rmu la for the input imp ed a nce is d erived and compa re d with ex isting formu las for sp he rical, cylindri ca l and pla na r geo me tri es. In add iti o n, th e e ffec t of co nt ac t be twee n th e p las ma a nd a me ta l ante nna is es timat ed in th e low frequ e ncy li mit for the case of an a nt e nn a biase d to th e point of ion s he at h co ll apse.

Slot Admittance for Compressible Plasma Layers

“…Fejer [1964] treats a charged oscillating sphere and he approximates a dipole antenna by an antiphase excitation of two such spheres. His results are similar to those of Wait [1964] for kpa ~ l. A dipole antenna of a finite radius is considered by Balmain [1965], and the electroacoustic radiation resistance approaches zero with decreasing acoustic velocity u. For dipole antennas separated from compressible plasma by an insulating cylinder or an ion sheath, the power transferred to the P mode is significantly decreased with increasing frequency and thickness of the insulating layers [Seshadri, 1965d].…”

“…The compressi· bility of the plasma affects the slot susceptance only to a minor extent, as can be seen from figure 4. However, Balmain [1965] observed significant changes of the antenna reactance for various temperatures of the plasma, and the present results will be examined more closely. The complexity of the present formulation makes an analytical examination of the admittance behavior difficult, and it was found expedient to compute the complex power flow from a parallelplate waveguide into a half space of compressible isotropic plasma.…”

On natural noises detected by antennas in plasmas

“…In the special case when small values of k give the dominant contribution in the integral giving R, the so-called hydrodynamic approximation can be used. This leads to the following explicit expression [Balmain, 1965] When the hydrohynamic with tensor pressure (or full adiabatic) approximation of eu is valid for calculating the resistance, one can use results by Meyer and Vernet [1974], which give also the variation with antenna orientation. For conditions typical of ionospheric experiments, this approximation gives correct results [Meyer-Vernet, 1978] for frequencies near the plasma and upper hybrid frequencies.…”

A short cylindrical antenna as a diagnostic probe for measuring collision frequencies in a collision-dominated non-Maxwellian plasma

“…The experimental results, for the most part, have been analyzed using the theory proposed by King, Harrison, and Denton [l] for an a.ntenna in a cold, lossy, isotropic plasma. I n order t o estimate the contribution from the electroacoustic mode to the a n t e m impedance in the vicinity of the pla.sma frequency, the results have also been compared with the theory proposed by Balmain [2] Cook and Edgar [lS], and by Iiuehl [19]. These aut.hors, however, have ignored collisional effects and, hence, their theory is not applicable to our experiments.…”