The formation and evolution of the electron strahl in the inner heliosphere

2021 ◽  
Author(s):  
Seong-Yeop Jeong ◽  
Daniel Verscharen ◽  
Vocks Christian ◽  
Christopher Owen ◽  
Robert Wicks ◽  
...  
Keyword(s):  
Solar Wind ◽  
Velocity Distribution Function ◽  
Electron Velocity ◽  
Electron Velocity Distribution ◽  
Electron Velocity Distribution Function ◽  
Coulomb Collisions ◽  
Spiral Geometry ◽  
Formation And Evolution ◽  
Radial Evolution ◽  
Inner Heliosphere

<p>The electrons in the solar wind exhibit an interesting kinetic substructure with many important implications for the overall energetics of the plasma in the heliosphere. We are especially interested in the formation and evolution of the electron strahl, a field-aligned beam of superthermal electrons, in the heliosphere. We develop a kinetic transport equation for typical heliospheric conditions based on a Parker-spiral geometry of the magnetic field. We present the results of our theoretical model for the radial evolution of the electron velocity distribution function (VDF) in the solar wind. We study the effects of the adiabatic focusing of energetic electrons, wave-particle interactions, and Coulomb collisions through a generalized kinetic equation for the electron VDF. We compare and contrast our results with the observed effects in the electron VDFs from space missions that explore the radial evolution of electrons in the inner heliosphere such as Helios, Parker Solar Probe, and Solar Orbiter.</p>

scholarly journals Electron two-stream instability and its application in solar and heliophysics

2016 ◽  
Vol 31 (19) ◽  
pp. 1630018 ◽  
Author(s):  
Haihong Che
Keyword(s):  
Solar Wind ◽  
Electron Beams ◽  
Langmuir Wave ◽  
Velocity Distribution Function ◽  
Electron Velocity ◽  
Radio Bursts ◽  
Electron Velocity Distribution ◽  
Electron Velocity Distribution Function ◽  
Collapse Potential ◽  
Stream Instability

It is well known that electron beams accelerated in solar flares can drive two-stream instability and produce radio bursts in the solar corona as well as in the interplanetary medium. Recent observations show that the solar wind likely originates from nanoflare-like events near the surface of the Sun where locally heated plasma escapes along open field lines into space. Recent numerical simulations and theoretical studies show that electron two-stream instability (ETSI) driven by nanoflare-accelerated electron beams can produce the observed nanoflare-type radio bursts, the non-Maxwellian electron velocity distribution function of the solar wind, and the kinetic scale turbulence in solar wind. This brief review focus on the basic theoretical framework and recent progress in the nonlinear evolution of ETSI driven by electron beams, including the formation of electron holes, Langmuir wave generation in warm plasma, and the nonlinear modulation instability and Langmuir collapse. Potential applications in heliophysics and astrophysics are discussed.

scholarly journals Absence of the strahl during times of slow wind

2017 ◽  
Vol 35 (1) ◽  
pp. 71-85 ◽  
Author(s):  
Chris Gurgiolo ◽  
Melvyn L. Goldstein
Keyword(s):  
Solar Wind ◽  
Solar Wind Speed ◽  
Velocity Distribution Function ◽  
Plasma Electron ◽  
Electron Velocity ◽  
Electron Velocity Distribution ◽  
Electron Velocity Distribution Function ◽  
Slow Wind ◽  
Cluster 2 ◽  
Statistical Noise

Abstract. It is not uncommon during periods when the solar wind speed is less than 425 km s−1 to observe near 1 AU no evidence of a strahl population in either the electron solar wind or within the foreshock. Estimating the fluid flow within each energy step returned from the Plasma Electron And Current Experiment (PEACE) on board Cluster-2 often finds that in slow wind the GSE spherical flow angles in energies above where there is a clear core/halo signature are often close to radial with no evidence of a field-aligned flow. This signifies the lack of a strahl presence in the electron velocity distribution function (eVDF). When there is no obvious strahl signature in the data, the electrons above the core/halo in energy appear to be unstructured and smeared in angle. This can either be interpreted as due to statistical noise in low counting rate situations or the result of intense scattering. Regions where the strahl is seen and not seen are often separated by a very thin boundary layer. These transitions in the spacecraft frame of reference can be quite rapid, generally occurring within one to two spins (4–8 s).

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