Critical values of parameter of pith-angle scattering particles in loss
cone in the near-Earth magnetotail estimation

Lvova E.A.
(Institute of Physics, State University, St. Petersburg, St. Petergof, 198904, Russia)

We performed trajectory calculations of charged particles with small
pitch-angle  in the magnetic field imitating the magnetic field in the
nightside. We have quantitatively estimated the conditions of pitch-angle
scattering of a particle the loss cone during single crossing of the
equatorial plane near magnetosphere. The critical values of  scattering
parameter K=Rc/r are shown to range between 8 to 3 while moving Earthward
from 12 to 4 c Re. Calculations were carried out both for particles
ensemble and characteristic trajectory, it was shown that Kcr  for an
ensemble of  particles could be accurately estimated based on Kcr  values
obtained for characteristic trajctory. The analytical approximation of Kcr
dependence on the equatorial field magnitude for various models and
various magnetosphere conditions was obtained. We also estimated the ratio
of precipitating particles flux to the trapped particles flux, for
different Kcr , to relate our results to date, obtained from spacecraft
observations of the isotropic boundaries. Protons with energy about tens
of meV and heavy ions with energy about meV were shown to have an
effective scattering at distance ~4 Re.