skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Comparison of electric dipole and magnetic loop antennas for exciting whistler modes

Abstract

The excitation of low frequency whistler modes from different antennas has been investigated experimentally in a large laboratory plasma. One antenna consists of a linear electric dipole oriented across the uniform ambient magnetic field B{sub 0}. The other antenna is an elongated loop with dipole moment parallel to B{sub 0}. Both antennas are driven by the same rf generator which produces a rf burst well below the electron cyclotron frequency. The antenna currents as well as the wave magnetic fields from each antenna are measured. Both the antenna currents and the wave fields of the loop antenna exceed that of the electric dipole by two orders of magnitude. The conclusion is that loop antennas are far superior to dipole antennas for exciting large amplitude whistler modes, a result important for active wave experiments in space plasmas.

Authors:
;  [1]
  1. Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)
Publication Date:
OSTI Identifier:
22599888
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AMPLITUDES; ANTENNAS; COMPARATIVE EVALUATIONS; CYCLOTRON FREQUENCY; CYCLOTRONS; DIPOLE MOMENTS; ELECTRIC DIPOLES; ELECTRONS; EXCITATION; MAGNETIC FIELDS; PLASMA; WHISTLER INSTABILITY; WHISTLERS

Citation Formats

Stenzel, R. L., and Urrutia, J. M. Comparison of electric dipole and magnetic loop antennas for exciting whistler modes. United States: N. p., 2016. Web. doi:10.1063/1.4960666.
Stenzel, R. L., & Urrutia, J. M. Comparison of electric dipole and magnetic loop antennas for exciting whistler modes. United States. doi:10.1063/1.4960666.
Stenzel, R. L., and Urrutia, J. M. 2016. "Comparison of electric dipole and magnetic loop antennas for exciting whistler modes". United States. doi:10.1063/1.4960666.
@article{osti_22599888,
title = {Comparison of electric dipole and magnetic loop antennas for exciting whistler modes},
author = {Stenzel, R. L. and Urrutia, J. M.},
abstractNote = {The excitation of low frequency whistler modes from different antennas has been investigated experimentally in a large laboratory plasma. One antenna consists of a linear electric dipole oriented across the uniform ambient magnetic field B{sub 0}. The other antenna is an elongated loop with dipole moment parallel to B{sub 0}. Both antennas are driven by the same rf generator which produces a rf burst well below the electron cyclotron frequency. The antenna currents as well as the wave magnetic fields from each antenna are measured. Both the antenna currents and the wave fields of the loop antenna exceed that of the electric dipole by two orders of magnitude. The conclusion is that loop antennas are far superior to dipole antennas for exciting large amplitude whistler modes, a result important for active wave experiments in space plasmas.},
doi = {10.1063/1.4960666},
journal = {Physics of Plasmas},
number = 8,
volume = 23,
place = {United States},
year = 2016,
month = 8
}
  • Antenna radiation patterns are an important property of antennas. Reciprocity holds in free space and the radiation patterns for exciting and receiving antennas are the same. In anisotropic plasmas, radiation patterns are complicated by the fact that group and phase velocities differ and certain wave properties like helicity depend on the direction of wave propagation with respect to the background magnetic field B{sub 0}. Interference and wave focusing effects are different than in free space. Reciprocity does not necessarily hold in a magnetized plasma. The present work considers the properties of various magnetic antennas used for receiving whistler modes. Itmore » is based on experimental data from exciting low frequency whistler modes in a large uniform laboratory plasma. By superposition of linear waves from different antennas, the radiation patterns of antenna arrays are derived. Plane waves are generated and used to determine receiving radiation patterns of different receiving antennas. Antenna arrays have radiation patterns with narrow lobes, whose angular position can be varied by physical rotation or electronic phase shifting. Reciprocity applies to broadside antenna arrays but not to end fire arrays which can have asymmetric lobes with respect to B{sub 0}. The effect of a relative motion between an antenna and the plasma has been modeled by the propagation of a short wave packet moving along a linear antenna array. An antenna moving across B{sub 0} has a radiation pattern characterized by an oscillatory “whistler wing.” A receiving antenna in motion can detect any plane wave within the group velocity resonance cone. The radiation pattern also depends on loop size relative to the wavelength. Motional effects prevent reciprocity. The concept of the radiation pattern loses its significance for wave packets since the received signal does not only depend on the antenna but also on the properties of the wave packet. The present results are of fundamental interest and of relevance to loop antennas in space.« less
  • The electromagnetic fields excited by circular loop antennas in a magnetized plasma in the whistler frequency range are simulated by the finite-difference time-domain method. The spatial structure of quasi-monochromatic fields excited in the near- and far-field zones by an antenna with a harmonic current, as well as the dynamics of the electromagnetic field excited by an antenna with a current in the form of a single video pulse, is studied. Simulations performed for a uniform plasma and uniform ambient magnetic field agree well with the results of theoretical analysis and model laboratory experiments performed on large-scale plasma devices.
  • Using the effective Lagrangian method, we analyze the electroweak corrections to the anomalous dipole moments of leptons from some special two-loop topological diagrams which are composed of neutralino-slepton (chargino-sneutrino) in the minimal supersymmetric extension of the standard model (MSSM). Considering the translational invariance of the inner loop momenta and the electromagnetic gauge invariance, we get all dimension six operators and derive their coefficients. After applying equations of motion to the external leptons, the anomalous dipole moments of leptons are obtained. The numerical results imply that there is a parameter space where the two-loop supersymmetric corrections to the muon anomalous dipolemore » moments may be significant.« less
  • We study the thermal noise caused by mechanical or thermomechanical dissipation in mirrors of interferometric gravitational wave antennas. We give relative figures of merit for arbitrary Hermite-Gauss or Laguerre-Gauss optical beams regarding the Brownian and thermoelastic noises (substrate and coating) in the infinite mirror approximation.