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Cyclotron- and Bounce-Resonance Scattering of Electrons Trapped in the Earth’s Magnetic Field

  • Charles S. Roberts
Conference paper
Part of the Astrophysics and Space Science Library book series (ASSL, volume 10)

Abstract

Pitch-angle diffusion into the loss cone is an important loss mechanism for radiation-zone electrons trapped in the magnetosphere. This paper examines two wave-particle interactions which are likely to be important for producing pitch-angle scattering. These are cyclotron-resonance scattering by whistler-mode disturbances and bounce-resonance scattering by disturbances having electric- or magnetic-field components parallel to the Earth’s magnetic field. Both mechanisms can operate effectively not only with sinusoidally varying disturbance fields but also with irregular, noise-like field fluctuations. The latter have rather wide-band power-spectral-density functions, and the strength of the scattering is proportional to the power present at the frequency appropriate to produce either cyclotron or bounce resonance. Irregular whistler-mode disturbances with r.m.s. magnetic-field fluctuations of order 10−3γ or higher are significant in producing rates of pitch-angle diffusion in agreement with observed electron lifetimes in the slot and outer electron zone. If the whistler-mode power-spectral-density function decreases rapidly with increasing frequency, then this mechanism may have difficulty in explaining the pitch-angle scattering of nearly equatorially mirroring electrons. Contributions from bounce-resonance scattering can also be significant for the pitch-angle diffusion of relativistic electrons. This requires irregular parallel electric-field fluctuations of order 0.01–0.1 V/ km r.m.s. or magnetic-intensity fluctuations of order 10−5–10−4 r.m.s. of the Earth’s magnetic intensity at the equator of the line of force of interest. The experimentally observed loss of radiation-zone electrons may actually be due to a combination of the two mechanisms, bounce resonance being more important for electrons mirroring near the magnetic equator and cyclotron resonance being dominant for electrons mirroring sufficiently far off the magnetic equator.

Keywords

Pitch Angle Relativistic Electron Trap Particle Magnetic Equator Whistler Wave 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© D. Reidel Publishing Company, Dordrecht, Holland 1968

Authors and Affiliations

  • Charles S. Roberts
    • 1
  1. 1.Bell Telephone Laboratories, Inc.Murray HillUSA

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