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Packets of cyclotron waves induced by electron beam injection from the space shuttle 2. Nonlinear theory
Author(s) -
Mourenas D.,
Béghin C.
Publication year - 1991
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/90rs01646
Subject(s) - physics , wave packet , harmonics , cyclotron , computational physics , beam (structure) , electron , atomic physics , optics , quantum mechanics , voltage
During the Spacelab 1 space shuttle mission, electron beam injection in the ionosphere produced a variety of radio waves. The most unusual kind of spectrum consisted of packets of cyclotron waves occurring at successive harmonics of a frequency F 0 close to the upper hybrid ƒ uh . A linear treatment of the generation mechanism has been proposed in a companion paper [ Mourenas and Béghin , this issue]. It was shown that the emissions consist of the well‐known electronic Bernstein modes, which are excited by an interaction between the neutralization return current and the ambient ionospheric plasma. The observed amplitude modulation of the cyclotron emissions around the fundamental wave at F 0 = n ƒ ce closest to ƒ uh has been explained in the frame of a model which shows that some of the generated waves packets can escort the space‐borne receiver. However, the observation of successive harmonic packets around pF 0 remained to be interpreted. To this end, a two‐dimensional single‐wave model of the nonlinear interaction between a finite size ring beam and an infinite homogeneous magnetized plasma is presented. A system of scaled equations is developed and solved analytically for the initial evolution and shows a good agreement with the linear theory. The system is then solved numerically. The solution shows that the single F 0 wave considered grows exponentially at the linear growth rate; then the wave potential saturates due to beam electron trapping, producing a power law spectrum of the higher pF 0 harmonics of the electric field very similar to what was observed experimentally.