Details

Autor(en) / Beteiligte

• VERSCHAREN, DANIEL
• BOUROUAINE, SOFIANE
• Chandran, Benjamin D G

Titel

INSTABILITIES DRIVEN BY THE DRIFT AND TEMPERATURE ANISOTROPY OF ALPHA PARTICLES IN THE SOLAR WIND

Ist Teil von

• The Astrophysical journal, 2013-08, Vol.773 (2), p.1-13

Ort / Verlag

United States

Erscheinungsjahr

2013

Link zum Volltext

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• We investigate the conditions under which parallel-propagating Alfven/ion-cyclotron (A/IC) waves and fast-magnetosonic/whistler (FM/W) waves are driven unstable by the differential flow and temperature anisotropy of alpha particles in the solar wind. We focus on the limit in which w sub(|| alpha ) [> ~] 0.25v sub(A), where w sub(|| alpha ) is the parallel alpha-particle thermal speed and v sub(A) is the Alfven speed. We derive analytic expressions for the instability thresholds of these waves, which show, e.g., how the minimum unstable alpha-particle beam speed depends upon w sub(|| alpha )/v sub(A), the degree of alpha-particle temperature anisotropy, and the alpha-to-proton temperature ratio. We validate our analytical results using numerical solutions to the full hot-plasma dispersion relation. Consistent with previous work, we find that temperature anisotropy allows A/IC waves and FM/W waves to become unstable at significantly lower values of the alpha-particle beam speed U sub( alpha ) than in the isotropic-temperature case. Likewise, differential flow lowers the minimum temperature anisotropy needed to excite A/IC or FM/W waves relative to the case in which U sub( alpha ) = 0. We discuss the relevance of our results to alpha particles in the solar wind near 1 AU.