Energetic electrons at Uranus: Bimodal diffusion in a satellite limited radiation belt
- California Inst. of Tech., Pasadena (USA)
The Voyager 2 cosmic ray experiment observed intense electron fluxes in the middle magnetosphere of Uranus. High counting rates in several of the solid-state detectors precluded in the normal multiple coincidence analysis used for cosmic ray observations, and the authors have therefore performed laboratory measurements of the single-detector response to electrons. These calibrations allow a deconvolution from the counting rate data of the electron energy spectrum between energies of about 0.7 and 2.5 MeV. They present model fits to the differential intensity spectra from observations between L values of 6 and 15. The spectra are well represented by power laws in kinetic energy with spectral indices between 5 and 7. The phase space density at fixed values of the first two adiabatic invariants generally increases with L, indicative of an external source. However, there are also local minima associated with the satellites Ariel and Umbriel, indicating either a local source or an effective source due to nonconservation of the first two adiabatic invariants. For electrons which mirror at the highest magnetic latitudes, the local minimum associated with Ariel is radically displaced from the minimum L of that satellite by {approximately}0.5. The latitude variation of the satellite absorption efficiency predicts that if satellite losses are replenished primarily by radial diffusion there should be an increasing pitch angle anisotropy with decreasing L. The uniformity in the observed anisotropy outside the absorption regions then suggests that it is maintained by pitch angle diffusion. The effective source due to pitch angle diffusion is insufficient to cause the phase space density minimum associated with Ariel. Model solutions of the simultaneous radial and pitch angle diffusion equation show that the displacement of the high-latitude Ariel signature is also consistent with a larger effective source.
- OSTI ID:
- 5192282
- Journal Information:
- Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 96:A4; ISSN 0148-0227; ISSN JGREA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
CALIBRATION
COINCIDENCE METHODS
COUNTING TECHNIQUES
DIFFUSION
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
FUNCTIONS
LABORATORIES
LEPTONS
MATHEMATICAL MODELS
MEASURING INSTRUMENTS
PLANETARY ATMOSPHERES
PLANETARY MAGNETOSPHERES
PLANETS
RADIATION BELTS
RADIATION DETECTORS
RADIATION FLUX
RESPONSE FUNCTIONS
SPACE VEHICLES
URANUS PLANET
VEHICLES
VOYAGER SPACE PROBES