A Quasi-linear Diffusion Model for Resonant Wave–Particle Instability in Homogeneous Plasma

Jeong, Seong Yeop; Verscharen, Daniel; Wicks, Robert T.; Fazakerley, A. N.

doi:10.3847/1538-4357/abb099

Cited by 32 publications

(36 citation statements)

References 62 publications

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“…The evolution of the main velocity moments, such as drifting or beaming speeds, and temperature components (parallel and perpendicular to the magnetic field) is confirmed by the numerical simulations, which also show that transient deformations of the distributions fade over time, while their initial shape (e.g., bi-Maxwellian with lower drifts for drifting components) is mainly restored during the relaxation [10,[21][22][23][24]. More elaborate QL diffusion theories attempting to reproduce transient deformations of the anisotropic distribution [25] are however complicated and restricted thus far to a limited approximation of treating the wave spectral intensity as fixed and not evolving in time, which make their implementation to fully describe the saturation of the fluctuations and relaxation of the anisotropic distribution not yet feasible.…”

Section: Introductionsupporting

confidence: 57%

Proton-Alpha Drift Instability of Electromagnetic Ion-Cyclotron Modes: Quasilinear Development

Shaaban

Lazar

Yoon

et al. 2021

Physics

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The ability of space plasmas to self-regulate through mechanisms involving self-generated fluctuations is a topic of high interest. This paper presents the results of a new advanced quasilinear (QL) approach for the instability of electromagnetic ion-cyclotron modes driven by the relative alpha-proton drift observed in solar wind. For an extended parametric analysis, the present QL approach includes also the effects of intrinsic anisotropic temperatures of these populations. The enhanced fluctuations contribute to an exchange of energy between proton and alpha particles, leading to important variations of the anisotropies, the proton-alpha drift and the temperature contrast. The results presented here can help understand the observational data, in particular, those revealing the local variations associated with the properties of protons and alpha particles as well as the spatial profiles in the expanding solar wind.

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Section: Introductionsupporting

confidence: 57%

Proton-Alpha Drift Instability of Electromagnetic Ion-Cyclotron Modes: Quasilinear Development

Shaaban

Lazar

Yoon

et al. 2021

Physics

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“…5) Another possible reason why a strahl may not be detected at 1 AU is because of plasma-wave instabilities that may have disrupted the strahl, (e.g. Gary and Saito, 2007;Kuzichev et al, 2019;Lopez et al, 2019;Vasko et al, 2019;Versharen et al, 2019;Jeong et al, 2020;Micera et al, 2020). Parameterization of instability thresholds is needed and then a matching of strahlchange locations with plasma-parameter changes is needed to test the instability possibility.…”

Section: Discussion: Interpretation Of Strahl-intensity Changes Assementioning

confidence: 99%

Exploring the Properties of the Electron Strahl at 1 AU as an Indicator of the Quality of the Magnetic Connection Between the Earth and the Sun

Borovsky

2021

Front. Astron. Space Sci.

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In this report some properties of the electron strahl at 1 AU are examined to assess the strahl at 272 eV as an indicator of the quality of the magnetic connection of the near-Earth solar wind to the Sun. The absence of a strahl has been taken to represent either a lack of magnetic connection to the corona or the strahl not surviving to 1 AU owing to scattering. Solar-energetic-electron (SEE) events can be used as indicators of good magnetic connection: examination of 216 impulsive SEE events finds that they are all characterized by strong strahls. The strahl intensity at 1 AU is statistically examined for various types of solar-wind plasma: it is found that the strahl is characteristically weak in sector-reversal-region plasma. In sector-reversal-region plasma and other slow wind, temporal changes in the strahl intensity at 1 AU are examined with 64 s resolution measurements and the statistical relationships of strahl changes to simultaneous plasma-property changes are established. The strahl-intensity changes are co-located with current sheets (directional discontinuities) with strong changes in the magnetic-field direction. The strahl-intensity changes at 1 AU are positively correlated with changes in the proton specific entropy, the proton temperature, and the magnetic-field strength; the strahl-intensity changes are anti-correlated with changes in the proton number density, the angle of the magnetic field with respect to the Parker-spiral direction, and the alpha-to-proton number-density ratio. Reductions in the strahl intensity are not consistent with expectations for a simple model of whistler-turbulence scattering. Reductions in the strahl intensity are mildly consistent with expectations for Coulomb scattering, however the strongest-observed plasma-change correlations are unrelated to Coulomb scattering and whistler scattering. The implications of the strahl-intensity-change analysis are that the change in the magnetic-field direction at a strahl change represents a change in the magnetic connection to the corona, resulting in a different strahl intensity and different plasma properties. An outstanding question is: Does an absence of an electron strahl represent a magnetic disconnection from the Sun or a poor strahl source in some region of the corona?

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“…In the near-Sun solar wind (at ∼34 R S ), Coulomb collisions only effectively scatter the strahl electrons with energies smaller than 250 eV (Horaites et al 2018;Boldyrev & Horaites 2019;. The scattering of the strahl at higher energies and the creation of the halo population are therefore attributed to other phenomena, including waveparticle interactions (Vocks et al 2005;Kajdič et al 2016;Verscharen et al 2019;Jagarlamudi et al 2020;Jeong et al 2020;Cattell et al 2021) and scattering by background turbulence (Pagel et al 2007;Saito & Gary 2007). Observational studies by Štverák et al (2009) and Halekas et al (2020) suggest that the halo is more prominent farther from the Sun, which could be the reason why the sunward deficit has not been observed at larger radial distances (Figure 5(a)).…”

Section: Ambipolar Electric Potential (φ R∞ )mentioning

confidence: 99%

Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions

Berčič

Maksimović

Halekas

et al. 2021

ApJ

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The solar wind escapes from the solar corona and is accelerated, over a short distance, to its terminal velocity. The energy balance associated with this acceleration remains poorly understood. To quantify the global electrostatic contribution to the solar wind dynamics, we empirically estimate the ambipolar electric field (E ∥) and potential (Φr,∞). We analyze electron velocity distribution functions (VDFs) measured in the near-Sun solar wind between 20.3 R S and 85.3 R S by the Parker Solar Probe. We test the predictions of two different solar wind models. Close to the Sun, the VDFs exhibit a suprathermal electron deficit in the sunward, magnetic-field-aligned part of phase space. We argue that the sunward deficit is a remnant of the electron cutoff predicted by collisionless exospheric models. This cutoff energy is directly linked to Φr,∞. Competing effects of E ∥ and Coulomb collisions in the solar wind are addressed by the Steady Electron Runaway Model (SERM). In this model, electron phase space is separated into collisionally overdamped and underdamped regions. We assume that this boundary velocity at small pitch angles coincides with the strahl break-point energy, which allows us to calculate E ∥. The obtained Φr,∞ and E ∥ agree well with theoretical expectations. They decrease with radial distance as power-law functions with indices α Φ = −0.66 and α E = −1.69. We finally estimate the velocity gained by protons from electrostatic acceleration, which equals 77% calculated from the exospheric models, and 44% from the SERM model.

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A Quasi-linear Diffusion Model for Resonant Wave–Particle Instability in Homogeneous Plasma

Cited by 32 publications

References 62 publications

Proton-Alpha Drift Instability of Electromagnetic Ion-Cyclotron Modes: Quasilinear Development

Proton-Alpha Drift Instability of Electromagnetic Ion-Cyclotron Modes: Quasilinear Development

Exploring the Properties of the Electron Strahl at 1 AU as an Indicator of the Quality of the Magnetic Connection Between the Earth and the Sun

Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions

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