A sleeve monopole antenna in a warm plasma

Egashira, Shinji; Morita, Y.

doi:10.1029/rs021i001p00159

Radio Science

1986

DOI: 10.1029/rs021i001p00159

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A sleeve monopole antenna in a warm plasma

Shinji Egashira¹,

Y. Morita²

Abstract: A sleeve monopole antenna whose length is comparable to a plasma wavelength has been studied both theoretically and experimentally in the frequency region for which there is electron plasma wave propagation. In taking account of Landau damping, it is found that if the sleeve length is larger than 25 Debye lengths, for the monopole of length 4 cm with a radius of 1 mm, then the input impedance becomes insensitive to further increase in sleeve length. The theoretical input impedances are found to be in good quan… Show more

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1989

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Cited by 2 publications

References 18 publications

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Loaded two‐element ring antenna for electron plasma waves

Morita¹,

Egashira²,

Honjoh³

1989

Radio Science

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A short, coil-loaded two-element ring antenna including a transmission line, immersed in a warm, isotropic plasma, is investigated as a boundary value problem in the frequency range where electron plasma waves exist. The wave potential of electron plasma waves launched from a two-element ring antenna has been enhanced by a factor of 4-6 in comparison with the case of an unloaded one-element ring antenna, when a suitable inductive load is inserted at the feeding point of element 2, and the distance between element 1 and element 2 is chosen as an optimum element spacing. Theory is substantiated by the experiments. In addition, the unidirectional radiation patterns of the antenna for electron plasma waves are predicted by the present theory.

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Loaded two‐element ring antenna for electron plasma waves

Morita¹,

Egashira²,

Honjoh³

1989

Radio Science

Self Cite

View full text Add to dashboard Cite

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High-frequency noise on antennas in plasmas

Stenzel

1989

Physics of Fluids B: Plasma Physics

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Fluctuations in plasmas at frequencies near the electron plasma frequency (ωp ) have been measured with in situ wire antennas. Such observations are important to the understanding of basic plasma properties (discrete versus collective effects) and the use of antennas in plasmas. The experiments are performed in a large (1 m diameter ×2 m) pulsed dc discharge and afterglow plasma (ne<1012 cm−3, kTe<5 eV) with a weak axial magnetic field (B0=5 G). The fluctuations are detected from wire antennas (length L≫radius a≳Debye length λD) with a low-noise microwave receiver. The observations reveal three different physical processes that determine the noise spectra: (i) single particle shot noise, (ii) collective oscillations by bounded sheath–plasma resonances, and (iii) noise enhancements by longitudinal plasma waves. The first phenomenon (shot noise) gives rise to broadband noise (ωωp) on both electric and magnetic antennas. In the evanescent regime (ω<ωp) , the shot noise is induced by random electron motions through distances of, at most, a collisionless skin layer (c/ωp) around the antenna. Recalling that electron transit-time effects cause absorption of waves in a collisionless skin layer (known as ‘‘anomalous’’ skin absorption) the present observation of a collisionless skin emission effect can also be understood by the equivalence of blackbody absorption and emission coefficients. The second phenomenon (sheath–plasma resonance) is observed as a narrow resonant enhancement in the shot noise below cutoff (ω<ωp) on electric antennas surrounded by sheaths or dielectrics. The series sheath–plasma resonance, usually identified from reflection/absorption measurements with incident waves, is established here, for the first time, as a feature of thermal emission spectra from antennas. The third phenomenon (plasma dielectric ε(ω,k)→0) produces a broad noise enhancement at ω≳ωp on electric antennas. It can only be observed in the open-loop voltage of dipoles measured with a high-impedance transformer between antenna and 50Ω transmission line. The enhanced noise is electrostatic, randomly polarized, but not significantly enhanced by the presence of energetic electron tails. Existing theories can describe the new observations qualitatively but not quantitatively.

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A sleeve monopole antenna in a warm plasma

Cited by 2 publications

References 18 publications

Loaded two‐element ring antenna for electron plasma waves

Loaded two‐element ring antenna for electron plasma waves

High-frequency noise on antennas in plasmas

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