Test-particle simulation of energetic electron-H₂O elastic collision along Saturn's magnetic field line around Enceladus

We examine the variation of energetic electron pitch angle distribution at the magnetic equator and loss rate of precipitated electrons into Saturn's atmosphere through pitch angle scattering due to elastic collisions with neutral H₂O along Saturn's magnetic field line around Enceladus. To examine the variation of those, we perform one-dimensional test-particle simulation when the co-rotating electron flux tube passes through the dense H₂O region in the vicinity of Enceladus (~6.4 min). We focus on 1 keV as a typical kinetic energy of the electrons in this study. The initial pitch angle distribution is assumed to be isotropic. Results show that the equatorial electron pitch angle distribution near the loss cone (<20° and >160°) decreases with time through pitch angle scattering due to elastic collisions. It is found that the electrons of ~11.4% to the total number of equatorial electrons at the initial condition are lost in ~380 s. The calculated loss time is twice faster than the loss time under the strong diffusion.