7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Electron physics and global processes in the heliosphere
M.E. Innocenti1, A. Micera1, D. Verscharen2, E. Boella3, A. Tenerani4, M.Velli51Department of Physics, Ruhr University Bochum, Germany 2Mullard Space Science Laboratory,
University College London, UK 3Department of Physics, University of Lancaster, UK 4Departmentof Physics, University of Texas at Austin, US 5Department of Earth, Planetary, and Space Sciences,
University of California, Los Angeles, USe-mail (speaker): mariaelena.innocenti@rub.deElectron scales in the heliosphere are orders ofmagnitude smaller than global heliospheric scales, bothin space and in time [1]. This notwithstanding, electron
physics is fundamental in shaping global heliosphericprocesses.
The fundamental non-locality of electron physics in the
heliosphere is highlighted by a number of recent works
and observations.
The recently observed sunward deficit in the electron
distribution is considered a signature of theinterplanetary potential that traps electrons over globalscales. The interplanetary potential traps the electrons
that leave the Sun with kinetic energy below a cut-off
value: these are the electrons that return towards the Sun.
The electrons giving rise to the deficit are the ones withenergy above the cut-off, which do not return [2,3]. The
sunward deficit can create the conditions for anelectron-scale microinstability, the whistler heat flux
instability [4], which contributes to further modify theelectron velocity distribution.
Another example of the fundamental role of electron
physics in global heliospheric dynamics is given by heat
flux regulation by electron scale microinstabilities. That
kinetic instabilities should contribute to heat-flux
regulation has been demonstrated decades ago with
Ulysses observations [5]. Recent Parker Solar Probe andSolar Orbiter observations, e.g. [6], together with
first-principle Particle-In-Cell simulations, e.g. [7], haveshown a directly link between electron microinstabilities
and scatter of strahl electrons, which results in reductionof the heat flux. Interestingly, also here global andelectron-scale processes are related non-trivially: it has
been demonstrated via semi-implicit expanding box
Particle-In-Cell simulations [8] that plasma expansion
can trigger electron-scale instabilities, which in turncontribute to heat flux regulation [9, 10].
In this talk, we will illustrate the above-mentioned links
between electron scale and global heliospheric dynamics
with the support of Particle In Cell simulations, both“standard” and Expanding Box.
References[1] Verscharen, D., Klein, K. G., & Maruca, B. A. (2019).
The multi-scale nature of the solar wind. Living Reviewsin Solar Physics, 16(1), 5.
[2] Berčič, L., Maksimović, M., Halekas, J. S., Landi, S.,Owen, C. J., Verscharen, D., ... & Stevens, M. L. (2021).
Ambipolar electric field and potential in the solar windestimated from electron velocity distributionfunctions. The Astrophysical Journal, 921(1), 83.
[3] Halekas, J. S., Berčič, L., Whittlesey, P., Larson, D.
E., Livi, R., Berthomier, M., ... & Pulupa, M. P. (2021).
The Sunward Electron Deficit: A Telltale Sign of theSun’s Electric Potential. The AstrophysicalJournal, 916(1), 16.
[4] Verscharen, D., Chandran, B. D. G., Boella, E.,Halekas, J., Innocenti, M. E., Jagarlamudi, V. K., ... &Whittlesey14, P. L. (2023). Electron-driven instabilities
in the solar wind. Plasma Waves in Space Physics:
Carrying On the Research Legacies of Peter Gary andRichard Thorne, 16648714.
[5] Scime, E. E., Bame, S. J., Feldman, W. C., Gary, S. P.,
Phillips, J. L., & Balogh, A. (1994). Regulation of thesolar wind electron heat flux from 1 to 5 AU: Ulysses
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[6] Cattell, C., Breneman, A., Dombeck, J., Short, B.,
Wygant, J., Halekas, J., ... & Pulupa, M. (2021). Parkersolar probe evidence for scattering of electrons in theyoung solar wind by narrowband whistler-modewaves. The Astrophysical journal letters, 911(2), L29.
[7] Micera, A., Zhukov, A. N., López, R. A., Innocenti,
M. E., Lazar, M., Boella, E., & Lapenta, G. (2020).
Particle-in-cell simulation of whistler heat-flux
instabilities in the solar wind: Heat-flux regulation andelectron halo formation. The Astrophysical Journal
Letters, 903(1), L23.
[8] Innocenti, M. E., Tenerani, A., & Velli, M. (2019). A
Semi-implicit Particle-in-cell Expanding Box Model
Code for Fully Kinetic Simulations of the Expanding
Solar Wind Plasma. The Astrophysical Journal, 870(2),66.
[9] Innocenti, M. E., Boella, E., Tenerani, A., & Velli, M.
(2020). Collisionless heat flux regulation via the electron
firehose instability in the presence of a core andsuprathermal population in the expanding solarwind. The Astrophysical Journal Letters, 898(2), L41.
[10] Micera, A., Zhukov, A. N., López, R. A., Boella, E.,
Tenerani, A., Velli, M., ... & Innocenti, M. E. (2021). On
the role of solar wind expansion as a source of whistler
waves: Scattering of suprathermal electrons and heat flux
regulation in the inner heliosphere. The AstrophysicalJournal, 919(1), 42.