Earth's Magnetotail as the Reservoir of Accelerated Single‐ and Multicharged Oxygen Ions Replenishing Radiation Belts
Acceleration of single‐ and multi‐charged oxygen ions in the perturbed Earth's magnetotail is investigated as the possible source of energetic heavy ions in the ring current. The numerical model is developed that allows evaluating the acceleration of oxygen ions O+‐O+8 in two possible scenarios of characteristic perturbations: (A) passage of multiple dipolarization fronts in the magnetotail; (B) passage of fronts followed by electromagnetic turbulence. It is shown that acceleration processes depend on particle charges as well as characteristic time scales of induced electric field variations. Maximum energies gained by oxygen ions correlate with values of their charges. Our simulations show that all kinds of single‐ and multiply charged heavy particles can be efficiently accelerated during multiple dipolarizations processes of the type (A) from initial energies 12 keV to maximum energies about several MeV. The gain of energies of heavy ions under the (B) scenario of magnetospheric perturbations is about 10% higher than in (A) scenario. The shapes of obtained in the model energy spectra were shown to be in agreement with experimental spectra in the range of L‐shells corresponding to ring/radiation belts. Therefore we conclude that the Earth's magnetotail can play the role of the depot where oxygen ions of both ionospheric and solar wind origin can be effectively accelerated during magnetic substorms to energies about several MeV and then populate the ring current and radiation belts of the Earth.