Collisional Thermalization of Hydrogen and Helium in Solar Wind Plasma

Дата и время публикации : 2013-11-21T16:44:59Z

Авторы публикации и институты :
Bennett A. Maruca
Stuart D. Bale
Luca Sorriso-Valvo
Justin C. Kasper
Michael L. Stevens

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: 5 pages, 2 figures, accepted to Physical Review Letters
Первичная категория: physics.space-ph

Все категории : physics.space-ph, astro-ph.SR

Краткий обзор статьи: In situ observations of the solar wind frequently show the temperature of $alpha$-particles (fully ionized helium), $T_alpha$, to significantly differ from that of protons (ionized hydrogen), $T_p$. Many heating processes in the plasma act preferentially on $alpha$-particles, even as collisions among ions act to gradually establish thermal equilibrium. Measurements from the $textit{Wind}$ spacecraft’s Faraday cups reveal that, at $r=1.0 textrm{AU}$ from the Sun, the observed values of the $alpha$-proton temperature ratio, $theta_{alpha p} equiv T_alpha,/,T_p$ has a complex, bimodal distribution. This study applied a simple model for the radial evolution of $theta_{alpha p}$ to these data to compute expected values of $theta_{alpha p}$ at $r=0.1 textrm{AU}$. These inferred $theta_{alpha p}$-values have no trace of the bimodality seen in the $theta_{alpha p}$-values measured at $r=1.0 textrm{AU}$ but are instead consistent with the actions of the known mechanisms for $alpha$-particle preferential heating. This result underscores the importance of collisional processes in the dynamics of the solar wind and suggests that similar mechanisms may lead to preferential $alpha$-particle heating in both slow and fast wind.

Category: Physics