Regulation of Solar Wind Electron Temperature Anisotropy by Collisions and Instabilities

Typical solar wind electrons are modeled as being composed of a dense but less energetic thermal “core” population plus a tenuous but energetic “halo” population with varying degrees of temperature anisotropies for both species. In this paper, we seek a fundamental explanation of how these solar win...

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Bibliographic Details
Published in:The Astrophysical journal 2024-11, Vol.975 (1), p.105
Main Authors: Yoon, Peter H., Salem, Chadi S., Klein, Kristopher G., Martinović, Mihailo M., López, Rodrigo A., Seough, Jungjoon, Sarfraz, Muhammad, Lazar, Marian, Shaaban, Shaaban M.
Format: Article
Language:English
Subjects:
Anisotropy
Collisions
Electron energy
Heliosphere
Instability
Interplanetary physics
Magnetic fields
Magnetohydrodynamic stability
Plasma instabilities
Solar physics
Solar wind
Solar wind electrons
Temperature
Temperature effects
Thermal energy
Wind effects
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Summary:Typical solar wind electrons are modeled as being composed of a dense but less energetic thermal “core” population plus a tenuous but energetic “halo” population with varying degrees of temperature anisotropies for both species. In this paper, we seek a fundamental explanation of how these solar wind core and halo electron temperature anisotropies are regulated by combined effects of collisions and instability excitations. The observed solar wind core/halo electron data in ( β ∥ , T ⊥ / T ∥ ) phase space show that their respective occurrence distributions are confined within an area enclosed by outer boundaries. Here, T ⊥ / T ∥ is the ratio of perpendicular and parallel temperatures and β ∥ is the ratio of parallel thermal energy to background magnetic field energy. While it is known that the boundary on the high- β ∥ side is constrained by the temperature anisotropy-driven plasma instability threshold conditions, the low- β ∥ boundary remains largely unexplained. The present paper provides a baseline explanation for the low- β ∥ boundary based upon the collisional relaxation process. By combining the instability and collisional dynamics it is shown that the observed distribution of the solar wind electrons in the ( β ∥ , T ⊥ / T ∥ ) phase space is adequately explained, both for the “core” and “halo” components.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ad7b09