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Yoon PH, López RA, Salem CS, Bonnell JW, Kim S. Non-Thermal Solar Wind Electron Velocity Distribution Function. ENTROPY (BASEL, SWITZERLAND) 2024; 26:310. [PMID: 38667863 PMCID: PMC11049069 DOI: 10.3390/e26040310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2024] [Revised: 03/24/2024] [Accepted: 03/27/2024] [Indexed: 04/28/2024]
Abstract
The quiet-time solar wind electrons feature non-thermal characteristics when viewed from the perspective of their velocity distribution functions. They typically have an appearance of being composed of a denser thermal "core" population plus a tenuous energetic "halo" population. At first, such a feature was empirically fitted with the kappa velocity space distribution function, but ever since the ground-breaking work by Tsallis, the space physics community has embraced the potential implication of the kappa distribution as reflecting the non-extensive nature of the space plasma. From the viewpoint of microscopic plasma theory, the formation of the non-thermal electron velocity distribution function can be interpreted in terms of the plasma being in a state of turbulent quasi-equilibrium. Such a finding brings forth the possible existence of a profound inter-relationship between the non-extensive statistical state and the turbulent quasi-equilibrium state. The present paper further develops the idea of solar wind electrons being in the turbulent equilibrium, but, unlike the previous model, which involves the electrostatic turbulence near the plasma oscillation frequency (i.e., Langmuir turbulence), the present paper considers the impact of transverse electromagnetic turbulence, particularly, the turbulence in the whistler-mode frequency range. It is found that the coupling of spontaneously emitted thermal fluctuations and the background turbulence leads to the formation of a non-thermal electron velocity distribution function of the type observed in the solar wind during quiet times. This demonstrates that the whistler-range turbulence represents an alternative mechanism for producing the kappa-like non-thermal distribution, especially close to the Sun and in the near-Earth space environment.
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Affiliation(s)
- Peter H. Yoon
- Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
| | - Rodrigo A. López
- Research Center in the Intersection of Plasma Physics, Matter, and Complexity (Pmc), Comisión Chilena de Energía Nuclear, Casilla 188-D, Santiago 7600713, Chile;
| | - Chadi S. Salem
- Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA; (C.S.S.); (J.W.B.)
| | - John W. Bonnell
- Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA; (C.S.S.); (J.W.B.)
| | - Sunjung Kim
- Astronomy and Space Sciences, Kyung Hee University, Yongin 17104, Gyeonggi, Republic of Korea;
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Hata M, Sano T, Sentoku Y, Nagatomo H, Sakagami H. Pulse duration constraint of whistler waves in magnetized dense plasma. Phys Rev E 2021; 104:035205. [PMID: 34654167 DOI: 10.1103/physreve.104.035205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Accepted: 08/31/2021] [Indexed: 06/13/2023]
Abstract
Interactions between large-amplitude laser light and strongly magnetized dense plasma have been investigated by one- and two-dimensional electromagnetic particle-in-cell simulations. Since whistler waves have no critical density, they can propagate through plasmas beyond the critical density in principle. However, we have found the propagation of whistler waves is restricted significantly by the stimulated Brillouin scattering. It is confirmed that the period during which the whistler wave can propagate in overcritical plasmas is proportional to the growth time of the ion-acoustic wave via the Brillouin instability. The allowable pulse duration of the whistler wave has a power-law dependence on the amplitude of the whistler wave and the external magnetic field.
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Affiliation(s)
- Masayasu Hata
- Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
- Kansai Photon Science Institute (KPSI), National Institutes for Quantum and Radiological Science and Technology (QST), Kizugawa, Kyoto 619-0215, Japan
| | - Takayoshi Sano
- Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Yasuhiko Sentoku
- Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Hideo Nagatomo
- Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Hitoshi Sakagami
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Gifu 509-5292, Japan
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López RA, Shaaban SM, Lazar M, Poedts S, Yoon PH, Micera A, Lapenta G. Particle-in-cell Simulations of the Whistler Heat-flux Instability in Solar Wind Conditions. THE ASTROPHYSICAL JOURNAL. LETTERS 2019; 882:10.3847/2041-8213/ab398b. [PMID: 32042401 PMCID: PMC7008930 DOI: 10.3847/2041-8213/ab398b] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In collision-poor plasmas from space, e.g., solar wind or stellar outflows, the heat flux carried by the strahl or beaming electrons is expected to be regulated by the self-generated instabilities. Recently, simultaneous field and particle observations have indeed revealed enhanced whistler-like fluctuations in the presence of counter-beaming populations of electrons, connecting these fluctuations to the whistler heat-flux instability (WHFI). This instability is predicted only for limited conditions of electron beam-plasmas, and has not yet been captured in numerical simulations. In this Letter we report the first simulations of WHFI in particle-in-cell setups, realistic for the solar wind conditions, and without temperature gradients or anisotropies to trigger the instability in the initiation phase. The velocity distributions have a complex reaction to the enhanced whistler fluctuations conditioning the instability saturation by a decrease of the relative drifts combined with induced (effective) temperature anisotropies (heating the core electrons and pitch-angle and energy scattering the strahl). These results are in good agreement with a recent quasilinear approach, and support therefore a largely accepted belief that WHFI saturates at moderate amplitudes. In the anti-sunward direction the strahl becomes skewed with a pitch-angle distribution decreasing in width as electron energy increases, which seems to be characteristic of self-generated whistlers and not to small-scale turbulence.
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Affiliation(s)
- R A López
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
| | - S M Shaaban
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
- Theoretical Physics Research Group, Physics Department, Faculty of Science, Mansoura University, 35516, Mansoura, Egypt
| | - M Lazar
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
- Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany
| | - S Poedts
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
| | - P H Yoon
- Institute for Physical Science and Technology, University of Maryland, College Park, MD, USA
- School of Space Research, Kyung Hee University, Republic of Korea
- Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea
| | - A Micera
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
- Solar-Terrestrial Centre of Excellence-SIDC, Royal Observatory of Belgium, B-1180 Brussels, Belgium
| | - G Lapenta
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
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