In this section
@article{Stansby:2019:0004-6361/201834900,
author = {Stansby, D and Perrone, D and Matteini, L and Horbury, T and Salem, C},
doi = {0004-6361/201834900},
journal = {Astronomy and Astrophysics},
title = {Alpha particle thermodynamics in the inner heliosphere fast solar wind},
url = {http://dx.doi.org/10.1051/0004-6361/201834900},
volume = {623},
year = {2019}
}
TY - JOUR
AB - Context. Plasma processes occurring in the corona and solar wind can be probed by studying the thermodynamic properties ofdifferent ion species. However, most in-situ observations of positive ions in the solar wind are taken at 1 AU, where information ontheir solar source properties may have been irreversibly erased.Aims. In this study we aimed to use the properties of alpha particles at heliocentric distances between 0.3 and 1 AU to study plasmaprocesses occurring at the points of observation, and to infer processes occurring inside 0.3 AU by comparing our results to previousremote sensing observations of the plasma closer to the Sun.Methods. We reprocessed the original Helios positive ion distribution functions, isolated the alpha particle population, and computedthe alpha particle number density, velocity, and magnetic field perpendicular and parallel temperatures. We then investigated the radialvariation of alpha particle temperatures in fast solar wind observed between 0.3 and 1 AU.Results. Between 0.3 and 1 AU alpha particles are heated in the magnetic field perpendicular direction, and cooled in the magneticfield parallel direction. Alpha particle evolution is bounded by the alpha firehose instability threshold, which provides one possiblemechanism to explain the observed parallel cooling and perpendicular heating. Closer to the Sun our observations suggest that thealpha particles undergo heating in the perpendicular direction, whilst the large magnetic field parallel temperatures observed at 0.3 AUmay be due to the combined effect of double adiabatic expansion and alpha particle deceleration inside 0.3 AU.
AU - Stansby,D
AU - Perrone,D
AU - Matteini,L
AU - Horbury,T
AU - Salem,C
DO - 0004-6361/201834900
PY - 2019///
SN - 0004-6361
TI - Alpha particle thermodynamics in the inner heliosphere fast solar wind
T2 - Astronomy and Astrophysics
UR - http://dx.doi.org/10.1051/0004-6361/201834900
UR - http://hdl.handle.net/10044/1/66829
VL - 623
ER -