Alpha Particle Temperature Anisotropy in Earth’s Magnetosheath

Alpha Particle Temperature Anisotropy in Earth’s Magnetosheath

Abstract In magnetized plasmas, temperature anisotropy manifests as distinct temperatures ( T ⊥ j , T ∥ j ). Numerous prior studies have demonstrated that as plasma beta ( β ∥ j ) increases, the range of temperature anisotropy ( R j = T ⊥ j / T ∥ j ) narrows. This limiting effect is conventionally t...

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Bibliographic Details
Published in:The Astrophysical journal Vol. 941; no. 1; pp. 12 - 20
Main Authors: DeWeese, Haley, Maruca, Bennett A., Qudsi, Ramiz A., Chasapis, Alexandros, Pultrone, Mark, Johnson, Elliot, Vines, Sarah K., Shay, Michael A., Matthaeus, William H., Gomez, Roman G., Fuselier, Stephen A., Giles, Barbara L., Gershman, Daniel J., Russell, Christopher T., Strangeway, Robert J., Burch, James L., Torbert, Roy B.
Format: Journal Article
Language:English
Published: Philadelphia The American Astronomical Society 01-12-2022
IOP Publishing
Subjects:
Alpha particles
Alpha rays
Anisotropy
Astrophysics
Contours
Cyclotrons
Growth rate
Helium
Magnetosheath
Planetary magnetospheres
Solar wind
Space plasmas
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Summary:Abstract In magnetized plasmas, temperature anisotropy manifests as distinct temperatures ( T ⊥ j , T ∥ j ). Numerous prior studies have demonstrated that as plasma beta ( β ∥ j ) increases, the range of temperature anisotropy ( R j = T ⊥ j / T ∥ j ) narrows. This limiting effect is conventionally taken as evidence that kinetic microinstabilities are active in the plasma, and has been previously observed for protons in the magnetosheath. This study is the first to use data from the Magnetic Multiscale Mission to investigate these instability-driven limits on alpha particle (ionized helium) anisotropy in Earth’s magnetosheath. The distribution of data over the ( β ∥ j , R j ) plane was plotted and shows the characteristic narrowing in the range of R j - values as β ∥ j increases. The contours of the data distribution align well with the contours of the constant growth rate for the ion cyclotron, mirror, parallel firehose, and oblique firehose instabilities, which were calculated using linear Vlasov theory.
Bibliography:The Sun and the Heliosphere
AAS40751
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ac9791