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Wave Excitation by Energetic Ring-distributed Electron Beams in the Solar Corona

Zhou, X., Muñoz, P. A., Büchner, J., & Liu, S. (2020). Wave Excitation by Energetic Ring-distributed Electron Beams in the Solar Corona. The Astrophysical Journal, 891(1): 92. doi:10.3847/1538-4357/ab6a0d.

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Genre: Journal Article

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Creators:
Zhou, Xiaowei1, Author
Muñoz, Patricio A., Author
Büchner, Jörg2, Author
Liu, Siming, Author
Affiliations:
1Max Planck Institute for Solar System Research, Max Planck Society, Justus-von-Liebig-Weg 3, 37077 Göttingen, DE, ou_1125546
2Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832289

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Abstract: We analyzed properties of waves excited by mildly relativistic electron beams propagating along the magnetic field with a ring-shape perpendicular momentum distribution in neutral and current-free solar coronal plasmas. These plasmas are subject to both the beam and the electron cyclotron maser instabilities driven by the positive momentum gradients of the ring-beam electron distribution in the directions parallel and perpendicular to the ambient magnetic field, respectively. To explore the related kinetic processes self-consistently, 2.5D fully kinetic particle-in-cell simulations were carried out. To quantify excited wave properties in different coronal conditions, we investigated the dependences of their energy and polarization on the ring-beam electron density and magnetic field. In general, electrostatic waves dominate the energetics of waves, and nonlinear waves are ubiquitous. In weakly magnetized plasmas, where the electron cyclotron frequency ω ce is lower than the electron plasma frequency ω pe, it is difficult to produce escaping electromagnetic waves with frequency ω > ω pe and small refractive index $| {ck}/\omega | \lt 1$ (k and c are the wavenumber and the light speed, respectively). Highly polarized and anisotropic escaping electromagnetic waves can, however, be effectively excited in strongly magnetized plasmas with ω ce/ω pe ≥ 1. The anisotropies of the energy, circular polarization degree (CPD), and spectrogram of these escaping electromagnetic waves strongly depend on the number density ratio of the ring-beam electrons to the background electrons. In particular, their CPDs can vary from left-handed to right-handed with the decrease of the ring-beam density, which may explain some observed properties of solar radio bursts (e.g., radio spikes) from the solar corona.

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Language(s): eng - English
Dates: 2020
Publication Status: Published in print
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Rev. Type: Peer
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Title: The Astrophysical Journal
Source Genre: Journal
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Publ. Info: Bristol; Vienna : IOP Publishing; IAEA
Pages: - Volume / Issue: 891 (1) Sequence Number: 92 Start / End Page: - Identifier: ISSN: 0004-637X
CoNE: https://pure.mpg.de/cone/journals/resource/954922828215_3