HR: 1340h
AN: SM53B-1286    [Abstracts]
TI: Ultra-relativistic Acceleration of Radiation Belt Electrons in Planetary Magnetospheres
AU: * Summers, D
EM: dsummers@math.mun.ca
AF: Memorial University of Newfoundland, Dept of Math and Stats, St John's, NF A1C 5S7, Canada
AU: Omura, Y
EM: omura@rish.kyoto-u.ac.jp
AF: Kyoto University, Research Institute for Sustainable Humanosphere, Uji, Kyoto, 611-0011, Japan
AB: The main mechanism for the formation of an electron radiation belt in a planetary magnetosphere is considered to be radial (cross-L) diffusion toward the planet from an external boundary. In this process the first and second adiabatic invariants are conserved and the third is violated. Typical electron energies in the Earth's outer radiation belt are E=400keV-10MeV ,while in Jupiter's inner magnetosphere electron energies are in the range E=1- 100MeV. Radial diffusion alone cannot explain the observed relativistic electron populations at Earth and Jupiter. For some time it has been thought that local acceleration due to electron cyclotron resonance with plasma waves(associated with violation of the first adiabatic invariant)could be important in energizing radiation belt electrons. We introduce a new particle acceleration mechanism called ultra-relativistic acceleration (URA). URA consists of electron energization due to a special form of nonlinear phase trapping by a coherent whistler-mode wave for electrons with an initial Lorentz factor exceeding a critical value; the critical value is the inverse of the wave frequency scaled by the cyclotron frequency at the magnetic equator of an assumed dipole field. Electrons that encounter multiple URA interactions together with relativistic turning acceleration(RTA) can undergo significant energization,e.g., for Earth(L=4) several-hundred keV electrons can be accelerated to a few MeV in about a second,while at Jupiter(L=8) several-hundred keV electrons can be accelerated to tens of MeV in seconds. We expect URA (and RTA) to be effective in the wider context of space and cosmic plasmas. Necessary conditions for significant energization by the URA and RTA mechanisms include a magnetic mirror geometry,a sufficient supply of seed electrons,and multiple whistler-mode wave packets of sufficient duration.
DE: 2720 Energetic particles: trapped
DE: 2774 Radiation belts
DE: 7807 Charged particle motion and acceleration
DE: 7845 Particle acceleration
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting