Electrons in the Young Solar Wind: First Results from the Parker Solar Probe. (arXiv:1912.02216v1 [astro-ph.SR])

Electrons in the Young Solar Wind: First Results from the Parker Solar Probe. (arXiv:1912.02216v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Halekas_J/0/1/0/all/0/1">J. S. Halekas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Whittlesey_P/0/1/0/all/0/1">P. Whittlesey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Larson_D/0/1/0/all/0/1">D. E. Larson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McGinnis_D/0/1/0/all/0/1">D. McGinnis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Maksimovic_M/0/1/0/all/0/1">M. Maksimovic</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Berthomier_M/0/1/0/all/0/1">M. Berthomier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kasper_J/0/1/0/all/0/1">J. C. Kasper</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Case_A/0/1/0/all/0/1">A. W. Case</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Korreck_K/0/1/0/all/0/1">K. E. Korreck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stevens_M/0/1/0/all/0/1">M. L. Stevens</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Klein_K/0/1/0/all/0/1">K. G. Klein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bale_S/0/1/0/all/0/1">S. D. Bale</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+MacDowall_R/0/1/0/all/0/1">R. J. MacDowall</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pulupa_M/0/1/0/all/0/1">M. P. Pulupa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Malaspina_D/0/1/0/all/0/1">D. M. Malaspina</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Goetz_K/0/1/0/all/0/1">K. Goetz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harvey_P/0/1/0/all/0/1">P. R. Harvey</a>

The Solar Wind Electrons Alphas and Protons experiment on the Parker Solar
Probe (PSP) mission measures the three-dimensional electron velocity
distribution function. We derive the parameters of the core, halo, and strahl
populations utilizing a combination of fitting to model distributions and
numerical integration for $sim 100,000$ electron distributions measured near
the Sun on the first two PSP orbits, which reached heliocentric distances as
small as $sim 0.17$ AU. As expected, the electron core density and temperature
increase with decreasing heliocentric distance, while the ratio of electron
thermal pressure to magnetic pressure ($beta_e$) decreases. These quantities
have radial scaling consistent with previous observations farther from the Sun,
with superposed variations associated with different solar wind streams. The
density in the strahl also increases; however, the density of the halo plateaus
and even decreases at perihelion, leading to a large strahl/halo ratio near the
Sun. As at greater heliocentric distances, the core has a sunward drift
relative to the proton frame, which balances the current carried by the strahl,
satisfying the zero-current condition necessary to maintain quasi-neutrality.
Many characteristics of the electron distributions near perihelion have trends
with solar wind flow speed, $beta_e$, and/or collisional age. Near the Sun,
some trends not clearly seen at 1 AU become apparent, including
anti-correlations between wind speed and both electron temperature and heat
flux. These trends help us understand the mechanisms that shape the solar wind
electron distributions at an early stage of their evolution.

The Solar Wind Electrons Alphas and Protons experiment on the Parker Solar
Probe (PSP) mission measures the three-dimensional electron velocity
distribution function. We derive the parameters of the core, halo, and strahl
populations utilizing a combination of fitting to model distributions and
numerical integration for $sim 100,000$ electron distributions measured near
the Sun on the first two PSP orbits, which reached heliocentric distances as
small as $sim 0.17$ AU. As expected, the electron core density and temperature
increase with decreasing heliocentric distance, while the ratio of electron
thermal pressure to magnetic pressure ($beta_e$) decreases. These quantities
have radial scaling consistent with previous observations farther from the Sun,
with superposed variations associated with different solar wind streams. The
density in the strahl also increases; however, the density of the halo plateaus
and even decreases at perihelion, leading to a large strahl/halo ratio near the
Sun. As at greater heliocentric distances, the core has a sunward drift
relative to the proton frame, which balances the current carried by the strahl,
satisfying the zero-current condition necessary to maintain quasi-neutrality.
Many characteristics of the electron distributions near perihelion have trends
with solar wind flow speed, $beta_e$, and/or collisional age. Near the Sun,
some trends not clearly seen at 1 AU become apparent, including
anti-correlations between wind speed and both electron temperature and heat
flux. These trends help us understand the mechanisms that shape the solar wind
electron distributions at an early stage of their evolution.

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