Energetic electron fluxes at Saturn from Cassini observations

Abstract

Energetic electron fluxes (18 keV-21 MeV) observed by the MIMI/LEMMS instrument on the Cassini mission during 2004 to 2008 are analyzed. We consider all 101 orbits and we select portions of the orbits that lie within 0.5 R_S of the magnetic equatorial plane, where R_S is Saturn's radius. We determine the average electron differential flux and integral flux at specified L-shells in the range 4.5 < L < 11. Further, comparisons are made between the observed fluxes and the corresponding relativistic self-limiting values developed from Kennel-Petschek theory. We find that at lower L-shells, L < 5, measured fluxes are much less than limiting values; at intermediate L-shells, 5 < L < 7, measured fluxes are close to the Kennel-Petschek limit; and at larger L-shells, 7 < L < 10, measured fluxes well exceed the limit. This suggests that (1) at lower L-shells particle injection is relatively weak, (2) at intermediate L-shells, sufficiently strong particle injections generate whistler mode waves to self-limit trapped fluxes, and (3) at larger L-shells, intense particle injections result in trapped particle fluxes well in excess of the Kennel-Petschek limit.