The Ph.D. colloquium by Ben Maruca will be held on Friday, April 13, at
9:00 AM in Phillips Auditorium.

At 10:30 AM, Ben will defend his thesis in Room M-240, 160 Concord Ave.

Talk Title: Instability-Driven Limits on Ion Temperature Anisotropy in
the Solar Wind: Observations and Linear Vlasov Theory

Abstract: Kinetic microinstabilities in the solar wind arise when its
non-thermal properties become too extreme.  This thesis project focused
specifically on the four instabilities associated with ion temperature
anisotropy: the cyclotron, mirror, and parallel and oblique firehose
instabilities.  Numerous studies have provided evidence that proton
temperature anisotropy in the solar wind is limited by the actions of
these instabilities.  For this project, a fully revised analysis of data
from the Wind spacecraft's Faraday cups and calculations from linear
Vlasov theory were used to extend these findings in two respects.
First, theoretical thresholds were derived for the alpha-particle
temperature anisotropy instabilities, which were then found to be
consistent with a statistical analysis of Wind alpha-particle data.
This suggests that alpha-particles, which constitute only about 5% of
ions in the solar wind, are nevertheless able to drive temperature
anisotropy instabilities.  Second, a statistical analysis of Wind proton
data found that proton temperature was significantly enhanced in plasma
unstable due to proton temperature anisotropy.  This implies that
extreme proton temperature anisotropies in solar wind at 1 AU arise from
ongoing anisotropic heating (versus cooling from, e.g., CGL double
adiabatic expansion).  Together, these results provide further insight
into the complex evolution of the solar wind's non-fluid properties.