Waves guided by density ducts in magnetoplasma in the nonresonant region of the whistler frequency range
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DIAGNOSTICS
Waves Guided by Density Ducts in Magnetoplasma in the Nonresonant Region of the Whistler Frequency Range V. A. Es’kina, T. M. Zaboronkovaa, b, A. V. Kudrina, and O. M. Ostafiychuka a b
Lobachevskii State University of Nizhni Novgorod, pr. Gagarina 23, Nizhni Novgorod, 603950 Russia Alekseev Nizhni Novgorod State Technical University, ul. Minina 24, Nizhni Novgorod, 603950 Russia e-mail: [email protected] Received June 18, 2014
Abstract—Guidance of azimuthally symmetric waves by cylindrical density ducts in magnetoplasma in the nonresonant region of the whistler frequency range is investigated. It is demonstrated that eigenmodes existing at the studied frequencies in ducts with enhanced plasma density allow simplified description that makes analysis of the features of their guided propagation much easier. The results of calculation of the dispersion characteristics and field structure of the whistler modes supported by such ducts are presented. DOI: 10.1134/S1063780X1502004X
1. INTRODUCTION Guided propagation of waves in the whistler frequency range in plasma channels (density ducts) in the presence of a static external magnetic field was investigated in a large number of works (see, e.g., [1–5] and references therein). Whistler waves supported by such structures have been intensely studied because of the important role that they play in many fundamental physical processes in the Earth’s ionosphere and magnetosphere [1, 2], as well as due to various applications, including VLF diagnostics of the near-Earth space [6], the use of the guiding properties of density ducts to control the characteristics of electromagnetic sources in magnetoplasma [3, 7–9], etc. An overwhelming majority of theoretical studies devoted to specific features of excitation and propagation of whistler waves in the presence of density ducts in a magnetized plasma deal with waves in the resonant region of the whistler range, which lies above the lower hybrid resonance frequency ωLH and allows the existence of quasi-electrostatic waves [10–16]. It was shown in those works that, in this frequency range, the ducts whose density is lower than the background level can support eigenmodes of different kinds, whereas ducts with enhanced density can support no more than one eigenmode with a volume-surface field structure (for each fixed value of the azimuthal index) and improper leaky modes. As to waves with frequencies below ωLH , investigation of their guided propagation in cylindrical density ducts has attracted little attention in the literature. In this work, we investigate the dispersion properties and field structure of the eigenmodes of density
ducts in the case where the angular frequency ω of the field lies in the nonresonant region
Ω H < ω < ωLH ω H ω p
(1)
of the whistler range. Here, Ω H is the ion gyrofrequency and ωH and ω p are the gyrofrequency and the plasma frequency of electrons, respectively (the time dependence of the field in the form exp(i ω t ) is assumed). Recall that the lower hybrid resonance frequency is ωLH
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