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Article

Acceleration of plasma in current sheet during substorm dipolarizations in the Earth’s magnetotail: Comparison of different mechanisms

Physics of Plasmas. 2019. Vol. 26. No. 4. P. 1-9.
Parkhomenko E. I., Malova H. V., Grigorenko E. E., Popov V., Petrukovich A. A., Delcourt D. C., Kronberg E. A., Daly P. W., Zelenyi L. M.

This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented
taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of
3 min; (B) single peak value of the normal magnetic component Bz occurring on the time scale of less than 1 min; (C) a sequence of rapid
jumps of Bz interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C)
followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale 1 s. In a frame of the
model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e, protons Hþ, helium Heþ, and oxygen Oþ
ions, accelerated by the above-mentioned processes (A)–(D). It is shown that Oþ ions can be accelerated mainly due to the mechanism (A);
Hþ and Heþ ions (and to some extent electrons) can be more effectively accelerated due to the mechanism (C) than the single dipolarization
(B). It is found that high-frequency electric and magnetic fluctuations accompanying multiple DFs (D) can strongly accelerate electrons e
and really weakly influence other populations of plasma. The results of modeling demonstrated clearly the distinguishable spatial and temporal
resonance character of particle acceleration processes. The maximum particle energies depending on the scale of the magnetic acceleration
region and the value of the magnetic field are estimated. The shapes of energy spectra are discussed.