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| Titel |
On the preferential heating and acceleration of helium ions: Collisions versus wave effects |
| VerfasserIn |
Sofiane Bourouaine, Eckart Marsch, Fritz Neubauer |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051339
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| Zusammenfassung |
| We show statistical results on the relative flow speed and the temperature ratio of alpha
particles and protons, and on their connections to the helium ion abundance, the collisional
age, and the power of transverse waves having frequencies between 0.01 and 1.0 normalized
to the proton gyrofrequency in the solar wind frame. It is found that the alpha-to-proton
temperature ratio, Tα-Tp, anti-correlates with the helium ion abundance. Despite a relatively
high collisional age and small wave power, the ratio Tα-Tp can reach comparatively high
values (even above 2) whenever the helium ion abundance is below about 0.02. In contrast,
the differential speed of alpha particles with respect to protons is correlated with
the total wave power and anti-correlated with the collisional age. Ultimately, the
individual heating of each ion species is positively correlated with the total wave
power. Our findings suggest that strong collisions could be efficient in reducing the
differential speed between alpha particles and protons, but appear not to be sufficient to
equalize the alpha and proton temperatures, i.e., to make Tα = Tp. This is a hint that
the local wave heating process is acting on a timescale shorter than the collision
time. |
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