HR: 11:41h
AN: SM32A-05 INVITED     [Abstracts]
TI: Particle Acceleration Associated with Large-Scale Current Systems
AU: * Ergun, R
EM: ree@lasp.colorado.edu
AF: University of Colorado, LASP, Boulder, CO 80303 United States
AB: In the last decade, observations from FAST, Freja, Polar, and Cluster II satellites have given a detailed picture of auroral particle acceleration. Electron acceleration comes in two basic classes: that driven by quasi-static parallel electric fields associated with global current systems and that driven by dynamic parallel electric fields associated with Alfvén waves. This talk concentrates on the former mechanism. Direct observations of the double layer electric fields and particle distributions suggest that it is feasible, if not probable, that strong double layers are a principal acceleration mechanism. Double layers in the upward and downward current regions are distinct. Those in the downward current region are concentrated in a monotonic potential ramp localized to ~10 Debye lengths along B. On the high-potential side of the ramp, an unstable electron beam is seen for roughly another 10 Debye lengths along B. The electron beam is rapidly stabilized in a region with intense electrostatic waves and nonlinear structures interpreted as electron phase-space holes. In the upward current region, observations have established that stationary, oblique double layers at the ionospheric boundary of the auroral cavity carry a substantial fraction (~10 to 50 percent) of the auroral potential. Numerical solutions to the Vlasov-Poisson equations of a planar, oblique double layer reproduces many of the properties of the observed electric fields, electron distributions, and ion distributions. These confirmed observations of double layers in both the upward and downward current regions provide compelling evidence that double layers and parallel electric fields may be a fundamental phenomena in astrophysical and space plasmas.
DE: 7807 Charged particle motion and acceleration
DE: 7815 Electrostatic structures
DE: 7839 Nonlinear phenomena (4400, 6944)
DE: 7845 Particle acceleration
DE: 7846 Plasma energization
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005