Seminar- Collisional Thermalization of Hydrogen and Helium in Solar Wind Plasma

11/20/2014 - 1:30pm
FL2- 1022

Collisional Thermalization of Hydrogen and Helium in Solar Wind Plasma

Ben Maruca, University of California, Berkeley

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In situ observations of solar wind plasma frequently show the temperature of alpha-particles (fully ionized helium) to significantly differ from that of protons (ionized hydrogen). Many heating processes in the solar wind act preferentially on alpha-particles, even as collisions among the plasma's ions act to gradually establish thermal equilibrium. Measurements from the Wind spacecraft's Faraday cups reveal that, at 1.0 AU from the Sun, the values of the alpha-proton temperature ratio has a complex, bimodal distribution. For this study, a simple, analytic model was developed for the evolution of this ratio with solar distance and then applied to each observation from the Wind Faraday cups to infer the value that the alpha-proton temperature ratio had been at 0.1 AU from the Sun. The distribution of these inferred values shows no trace of the bimodality observed at 1.0 AU but is instead consistent with 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.

Thursday, November 20, 2014

Time: 1:30pm

Building: FL2 - 1022