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Article Dans Une Revue Space Science Reviews Année : 2018

Electron Power-Law Spectra in Solar and Space Plasmas

Résumé

Particles are accelerated to very high, non-thermal energies in solar and space plasma environments. While energy spectra of accelerated electrons often exhibit a power law, it remains unclear how electrons are accelerated to high energies and what processes determine the power-law index delta . Here, we review previous observations of the power-law index delta in a variety of different plasma environments with a particular focus on sub-relativistic electrons. It appears that in regions more closely related to magnetic reconnection (such as the `above-the-looptop' solar hard X-ray source and the plasma sheet in Earth's magnetotail), the spectra are typically soft (delta ≳4). This is in contrast to the typically hard spectra (delta ≲4) that are observed in coincidence with shocks. The difference implies that shocks are more efficient in producing a larger non-thermal fraction of electron energies when compared to magnetic reconnection. A caveat is that during active times in Earth's magnetotail, delta values seem spatially uniform in the plasma sheet, while power-law distributions still exist even in quiet times. The role of magnetotail reconnection in the electron power-law formation could therefore be confounded with these background conditions. Because different regions have been studied with different instrumentations and methodologies, we point out a need for more systematic and coordinated studies of power-law distributions for a better understanding of possible scaling laws in particle acceleration as well as their universality.

Dates et versions

hal-03729609 , version 1 (20-07-2022)

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Mitsuo Oka, J. Birn, Marina Battaglia, C. C. Chaston, S. M. Hatch, et al.. Electron Power-Law Spectra in Solar and Space Plasmas. Space Science Reviews, 2018, 214, ⟨10.1007/s11214-018-0515-4⟩. ⟨hal-03729609⟩
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