Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 72, p. 33-38 (2025)
ACCELERATION OF CHARGED PARTICLES IN TURBULENT PLASMA FLOWS
Lyudmila KOZAK, DSc (Phys. & Math.), Prof.
ORCID ID: 0000-0001-9448-0030
е-mail: kozakliudmyla@knu.ua
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine,
Space Research Institute under NAS of Ukraine and State Space Agency of Ukraine, Kyiv, Ukraine
Bohdan PETRENKO, PhD
ORCID ID: 0000-0003-1073-0130
e-mail: bogdanart96@gmail.com
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine,
Space Research Institute under NAS of Ukraine and State Space Agency of Ukraine, Kyiv, Ukraine
Nazar KHALIMONENKO, Student
e-mail: nazarfifa2014@gmail.com
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
Abstract
Background. The acceleration of charged particles in space plasma is a key process that shapes the energy spectra of solar particles and cosmic rays. The most important mechanisms are diffusive shock acceleration (Fermi-I) at shock fronts and stochastic acceleration (Fermi-II) in turbulent environments. Their efficiency strongly depends on plasma parameters in different cosmic regions: the solar corona, the solar wind, and the Earth’s magnetosphere.
Methods. To investigate stochastic proton acceleration, a test-particle approach was applied within a stochastic model of turbulent diffusion. The simulation involved 5000 particles with an initial normalized momentum. The number of integration steps was set to 100 with a time step of 1 s. The momentum diffusion coefficient was specified separately for each environment: 0.02 for the solar corona, 0.015 for the solar wind, and 0.01 for the Earth’s magnetosphere.
Results. Time evolution of the average normalized momentum and particle energy distributions was obtained. In the solar corona, the most
intensive momentum growth and the formation of extended power-law distribution tails were observed, consistent with fluxes reaching energies up to hundreds of MeV. In the solar wind, the efficiency of stochastic acceleration was lower: spectra exhibited a limited energy increase up to hundreds of keV, in agreement with observations of interplanetary particle fluxes. In the Earth’s magnetosphere, the average momentum grew the slowest, and spectra had shorter tails; however, local processes (magnetic reconnection, dipolarization, plasmoids) provided additional acceleration of electrons and ions up to tens–hundreds of keV.
Conclusions. The results confirm the universality of Fermi mechanisms: in the corona they produce high energies at CME shock fronts and in turbulent loops; in the solar wind stochastic “re-acceleration” on Alfvén waves dominates; in the Earth’s magnetosphere Fermi processes operate on smaller scales in reconnection regions. Thus, differences in plasma parameters determine the efficiency of acceleration, but the underlying physical principles remain common across all environments.
Key words
Cosmic plasma, particle acceleration, Fermi mechanisms, solar corona, solar wind, Earth’s magnetosphere, turbulence, numerical modelling.
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