- 1Ruhr-Universität Bochum, Institut für Theoretische Physik, Computational Plasma Physics, Germany (mahmoud.ibrahim@ruhr-uni-bochum.de)
- 2University of Arizona, Department of Planetary Sciences, Lunar and Planetary Laboratory, 1629 E University Blvd, Tucson, AZ 85721, USA (mahmoudibrahim@arizona.edu)
- 3Department of Physics, Faculty of Science, Benha University, Benha 13518, Egypt (mahmoud.afify@fsc.bu.edu.eg)
Discoveries by Parker Solar Probe (PSP) highlight the significance of nonthermal distributions in triggering ion-scale instabilities (Verniero et al. 2020, 2022; An et al. 2024; Liu et al. 2024). In this study, we show how the electron nonthermal (kappa) distribution could change the onset threshold of the ion-acoustic instability (IAI) recently observed by PSP (Mozer et al. 2021, 2023; Kellogg et al. 2024) between 15 and 25 solar radii and modeled by Afify et al. (2024). We perform analytical studies and kinetic simulations using the Vlasov-Poisson code with a parameter regime relevant to PSP observations. A setup of kappa-distributed electrons and two counterstreaming Maxwellian ion distributions (a core and a beam) is shown to be unstable w.r.t. the IAI, however, the electron-to-core and beam-to-core temperature ratios are slightly different from those recorded by PSP. The simulated growth rates have been validated by the kinetic theory. In the saturation regime, we do observe the formation of ion holes in the beam phase-space density. With large kappa values, the ion-acoustic waves interacted substantially with the beam, for instance, κ = 20, and shifted away from the beam with lower kappa values, for instance, κ = 5 and 7. Our findings confirm that protons exhibit reduced resonance in the presence of kappa electrons, and the electron heating observed by PSP during the presence of IAI is not replicated in our simulation (Mozer et al. 2022).
References
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How to cite: Afify, M. S., Dreher, J., O'Neill, S., and Innocenti, M. E.: The role of nonthermal electron distribution in triggering electrostatic ion-acoustic instability near the Sun, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2097, https://doi.org/10.5194/egusphere-egu25-2097, 2025.
