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Stimulated amplification of ULF waves by magnetospheric injections of plasma clouds and particle beams


  • Harold B. Liemohn


Our understanding of wave particle interactions in the magnetosphere has progressed to the point where it may be possible to stimulate wave amplification at ULF (about 0.1 to 10 Hz) by disturbing the cyclotron resonance conditions through catalytic injections of plasma clouds or particle beams. Modification of the interaction can be achieved by the introduction of localized clouds of plasma that reduce the phase velocity of the waves and cause enhanced amplification by lowering the resonance velocity. Alternatively, direct injection of hot energetic particle beams can also appreciably alter the local amplification characteristics. Different methods for injecting clouds of lithium plasma and proton beams have been modeled quantitatively to assess their relative merits. Amplifications of many tens of decibels appear to be feasible with lithium clouds of only 1 to 2 kg of material. With present technology the beam diameter from a conventional particle gun on board a satellite or rocket is too small for an effective interaction, but appreciable amplification is indicated. Such a prospect has great significance. First, it offers a direct test of the fundamental physical processes that are believed to control the state of the magnetosphere. Second, controlled injections might be used to stimulate artificial amplification of ULF emissions on command and allow them to be used as a wide-area communication system.

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