Electron Heat Flux Instabilities in the Inner Heliosphere: Radial Distribution and Implication on the Evolution of the Electron Velocity Distribution Function

Sun, Heyu; Zhao, Jinsong; Liu, Wen; Voitenko, Yuriy; Pierrard, Viviane; Shi, Chen; Yao, Yuhang; Xie, Huasheng; Wu, D. J.

doi:10.3847/2041-8213/ac0f02

Cited by 14 publications

(24 citation statements)

References 46 publications

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“…We now investigate the possibility for the oblique FM/W instability to scatter strahl electrons into the halo as the solar wind expands into the heliosphere. The oblique FM/W instability has received major attention lately as a mechanism to explain the halo formation (Vasko et al 2019;López et al 2020;Jeong et al 2020;Micera et al 2020Micera et al , 2021Halekas et al 2021;Sun et al 2021). For this investigation, we compare our fit parameters from Section 4.2 with the theoretically predicted threshold for the oblique FM/W instability in the low-β c regime given by .…”

Section: Oblique Fast-magnetosonic/whistler Instabilitymentioning

confidence: 95%

“…However, at large distances from the Sun, other mechanisms must be considered for local strahl scattering (Horaites et al 2018b(Horaites et al , 2019. For instance, the strahl-driven oblique fast-magnetosonic/whistler (FM/W) instability has recently received much attention as such a mechanism (Vasko et al 2019;López et al 2020;Jeong et al 2020;Micera et al 2020Micera et al , 2021Halekas et al 2021;Sun et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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The Kinetic Expansion of Solar-Wind Electrons: Transport Theory and Predictions for the very Inner Heliosphere

Jeong,

Verscharen,

Vocks

et al. 2022

Preprint

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We propose a transport theory for the kinetic evolution of solar-wind electrons in the heliosphere. We derive a gyro-averaged kinetic transport equation that accounts for the spherical expansion of the solar wind and the geometry of the Parker-spiral magnetic field. To solve our three-dimensional kinetic equation, we develop a mathematical approach that combines the Crank-Nicolson scheme in velocity space and a finite-difference Euler scheme in configuration space. We initialize our model with isotropic electron distribution functions and calculate the kinetic expansion at heliocentric distances from 5 to 20 solar radii. In our kinetic model, the electrons evolve mainly through the combination of the ballistic particle streaming, the magnetic mirror force, and the electric field. By applying fits to our numerical results, we quantify the parameters of the electron strahl and core part of the electron velocity distributions. The strahl fit parameters show that the density of the electron strahl is around 7% of the total electron density at a distance of 20 solar radii, the strahl bulk velocity and strahl temperature parallel to the background magnetic field stay approximately constant beyond a distance of 15 solar radii, and β s (i.e., the ratio between strahl parallel thermal pressure to the magnetic pressure) is approximately constant with heliocentric distance at a value of about 0.02. We compare our results with data measured by Parker Solar Probe. Furthermore, we provide theoretical evidence that the electron strahl is not scattered by the oblique fast-magnetosonic/whistler instability in the near-Sun environment.

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Section: Oblique Fast-magnetosonic/whistler Instabilitymentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

The Kinetic Expansion of Solar-Wind Electrons: Transport Theory and Predictions for the very Inner Heliosphere

Jeong,

Verscharen,

Vocks

et al. 2022

Preprint

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“…This strahl-driven instability has recently received a significant amount of attention in the literature as a local strahl scattering mechanism. Linear and quasi-linear theories as well as numerical particle-incell (PIC) simulations support this picture (López et al 2020;Jeong et al 2020;Micera et al 2020Micera et al , 2021Sun et al 2021).…”

Section: Introductionmentioning

confidence: 94%

The Stability of the Electron Strahl against the Oblique Fast-magnetosonic/Whistler Instability in the Inner Heliosphere

Jeong,

Abraham,

Verscharen

et al. 2022

Preprint

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We analyze the micro-kinetic stability of the electron strahl in the solar wind depending on heliocentric distance. The oblique fast-magnetosonic/whistler (FM/W) instability has emerged in the literature as a key candidate mechanism for the effective scattering of the electron strahl into the electron halo population. Using data from Parker Solar Probe (PSP) and Helios, we compare the measured strahl properties with the analytical thresholds for the oblique FM/W instability in the low-and high-β c regimes, where β c is the ratio of the core parallel thermal pressure to the magnetic pressure. Our PSP and Helios data show that the electron strahl is on average stable against the oblique FM/W instability in the inner heliosphere. Our analysis suggests that the instability, if at all, can only be excited sporadically and on short timescales. We discuss the caveats of our analysis and potential alternative explanations for the observed scattering of the electron strahl in the solar wind. Furthermore, we recommend the numerical evaluation of the stability of individual distributions in the future to account for any uncertainties in the validity of the analytical expressions for the instability thresholds.

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“…The physical meaning of P s (v) is energy emission/absorption per unit of phase space, per unit of electromagnetic energy, and per unit of time. The expression (20) has been used to identify Landau and/or cyclotron resonant interactions in studies of Alfvén-mode waves and of electron/ion beam instabilities (e.g., He et al 2019;Duan et al 2020;He et al 2020;Sun et al 2021;Liu et al 2021;Kitamura et al 2021). P s (v) is the energy transfer rate in three-dimensional (3D) velocity space, and P st is the energy transfer rate integrated in 3D velocity space.…”

Section: Energy Transfer and Energy Transfer Rate Of The Monochromati...mentioning

confidence: 99%

“…In most of the heliosphere and in astrophysical plasma environments, such as the solar corona, the solar wind, the interstellar medium, and the intracluster medium, collisionless wave-particle interactions, instead of collisions among particles, play a key role in determining the particle dynamics. On one hand, a nonequilibrium particle velocity distribution function can release the free energy into plasma waves through wave-particle interactions (e.g., Verscharen et al 2019;Sun et al 2021;Liu et al 2021). On the other hand, plasma waves can energize particles, leading to plasma heating and particle acceleration (e.g., Marsch 2006).…”

Section: Introductionmentioning

confidence: 99%

Quantifying Wave–Particle Interactions in Collisionless Plasmas: Theory and Its Application to the Alfvén-mode Wave

Zhao

Lee

Xie

et al. 2022

ApJ

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Wave–particle interactions can induce energy transfer at different timescales in collisionless plasmas, which leads to the reshaping of the particle velocity distribution function. Therefore, how to quantify wave–particle interactions is one of the fundamental problems in the heliosphere and in astrophysical plasmas. This study proposes a systematic method to quantify linear wave–particle interactions based on the Vlasov–Maxwellian model. We introduce energy transfer rates with various expressions by using perturbed electric fields and perturbed particle velocity distribution functions. Then, we use different expressions of the energy transfer rate to perform a comprehensive investigation of wave–particle interactions of the Alfvén-mode wave. We clarify the physical mechanisms responsible for the damping of the Alfvén-mode wave in wavevector space. Moreover, this study exhibits for the first time evident signatures of wave–particle interactions between Alfvén-mode waves and resonant/nonresonant particles in the velocity space. These resonant and nonresonant particles can induce energy transfer in opposite directions, which leads to self-regulation of the particle velocity distribution function. Furthermore, this study exhibits a comprehensive dependence of wave–particle interactions of the Alfvén-mode wave on the wavenumber and plasma beta (the ratio between the plasma thermal pressure and the magnetic pressure). These results illustrate that the proposed method would be very useful for quantifying different types of linear wave–particle interactions of an arbitrary wave mode.

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Electron Heat Flux Instabilities in the Inner Heliosphere: Radial Distribution and Implication on the Evolution of the Electron Velocity Distribution Function

Cited by 14 publications

References 46 publications

The Kinetic Expansion of Solar-Wind Electrons: Transport Theory and Predictions for the very Inner Heliosphere

The Kinetic Expansion of Solar-Wind Electrons: Transport Theory and Predictions for the very Inner Heliosphere

The Stability of the Electron Strahl against the Oblique Fast-magnetosonic/Whistler Instability in the Inner Heliosphere

Quantifying Wave–Particle Interactions in Collisionless Plasmas: Theory and Its Application to the Alfvén-mode Wave

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