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| Titel |
Instability of the Parallel-Propagating Alfvén/Ion-Cyclotron Wave Driven by Drifting Alpha Particles in High-Beta Solar Wind Streams |
| VerfasserIn |
Daniel Verscharen, Sofiane Bourouaine, Benjamin D. G. Chandran |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072636
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| Zusammenfassung |
| Alpha particles are known to drift with respect to the protons along the background magnetic
field in the fast solar wind. Their typical drift speed is observed to be limited to a value of
order the local proton Alfvén speed vA as long as collisional deceleration can be neglected.
Since vA decreases with increasing distance from the Sun, a continuous deceleration takes
place converting the drift energy to other forms of energy such as thermal energy or wave
energy.
We derive an instability of the parallel-propagating Alfvén/ion-cyclotron mode driven by
drifting alpha particles in a high-beta plasma (β -³ 2). To the best of our knowledge, this
alpha-particle-driven drift instability has not been described previously, although it is
similar in several respects to the well-studied cosmic-ray streaming instability. Using
quasilinear theory, we derive an approximate analytic expression for the instability
threshold. We compare this expression with numerical solutions of the full hot-plasma
dispersion relation and find good agreement. The described instability is a result of the
competition between driving by resonant alpha particles and damping by resonant
protons.
Other drift instabilities are known to set “speed limits” to the relative drift of ion species
in the solar wind depending on the required plasma parameters. We present a comparison
with measured drift speeds and show that the instability threshold of the parallel Alfvénic
drift instability indeed limits the alpha particle drift in high-beta fast-solar-wind streams. |
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