Preferential Acceleration of Heavy Ions in a Spontaneously Fragmenting Flare Current Sheet

0556101 - ASÚ 2023 RIV GB eng J - Journal Article
Kramoliš, D. - Bárta, Miroslav - Varady, Michal - Bučík, R.
Preferential Acceleration of Heavy Ions in a Spontaneously Fragmenting Flare Current Sheet.
Astrophysical Journal. Roč. 927, č. 2 (2022), č. článku 177. ISSN 0004-637X. E-ISSN 1538-4357
R&D Projects: GA ČR(CZ) GA19-09489S; GA ČR(CZ) GC20-09922J
Institutional support: RVO:67985815
Keywords : solar energetic particles * magnetic reconnection mechanism * current-layer fragmentation
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 4.9, year: 2022
Method of publishing: Open access

We study the ion acceleration in a mesoscale, spontaneously fragmenting flare current sheet (SFCS) characterized by the presence of a plasmoid cascade. The main subject of our investigation is to determine whether and how plasmoid cascades at intermediate scales in a fragmented current sheet of a solar flare can impact the (preferential) acceleration of specific ions. The time evolution of the SFCS is obtained from high-resolution 2.5D MHD simulations. The ion trajectories (in the background fields resulting from the MHD model), energies, and pitch angles are calculated using a relativistic test-particle code based on the half-acceleration-rotation-half-acceleration method. For light ions, the main acceleration effects of electromagnetic fields within the SFCS are analyzed using the guiding center approximation. We identify regions with the most-efficient ion acceleration within the SFCS, the accelerator efficiency, and spectra of the accelerated ions. The influence of the charge-to-mass ratio on ion behavior is also studied and resulting ion abundances are compared with observational data. The main ion acceleration takes place in the regions with a strong polarization term, which is part of the first-order Fermi acceleration. Because the term is mass dependent, heavier ions undergo preferential acceleration. The ion energy spectra, abundance-enhancement factors, and differential fluxes, obtained from the model, exhibit power-law profiles, in agreement with observed solar energetic particle events. Nonetheless, the obtained slopes for the abundance-enhancement factor do not exactly match the observed data. The computed slopes and profiles are not sensitive to changes in the initial plasma temperature.
Permanent Link: http://hdl.handle.net/11104/0330922