2 research outputs found

    Generation of Suprathermal Electrons by Collective Processes in Collisional Plasma

    Get PDF
    The ubiquity of high-energy tails in the charged particle velocity distribution functions observed in space plasmas suggests the existence of an underlying process responsible for taking a fraction of the charged particle population out of thermal equilibrium and redistributing it to suprathermal velocity and energy ranges. The present Letter focuses on a new and fundamental physical explanation for the origin of suprathermal electron distribution function in a highly collisional plasma. This process involves a newly discovered electrostatic bremsstrahlung emission that is effective in a plasma in which binary collisions are present. The steady-state electron velocity distribution function dictated by such a process corresponds to a Maxwellian core plus a quasi-inverse power-law tail, which is a feature commonly observed in many space plasma environment. In order to demonstrate this, the system of self-consistent particle- and wave- kinetic equations are numerically solved with an initially Maxwellian electron velocity distribution and Langmuir wave spectral intensity, which is a state that does not reflect the presence of electrostatic bremsstrahlung process, and hence not in force balance. The electrostatic bremsstrahlung term subsequently drives the system to a new force-balanced steady state. After a long integration period it is demonstrated the initial Langmuir fluctuation spectrum is modified, which in turn distorts the initial Maxwellian electron distribution into a velocity distribution that resembles the said core-suprathermal velocity distribution. Such a mechanism may thus be operative at the coronal source region, which is characterized by high collisionality.Comment: 7 pages, 2 figures. Published at: The Astrophysical Journal Letters, Volume 849, Number 2, L30. url: https://doi.org/10.3847/2041-8213/aa956

    Parker Solar Probe Observations of Near-f Ce Harmonic Emissions in the Near-Sun Solar Wind and Their Dependence on the Magnetic Field Direction

    Get PDF
    Wave emissions at frequencies near electron gyrofrequency harmonics are observed at small heliocentric distances below about 40 R ☉ and are known to occur in regions with quiescent magnetic fields. We show the close connection of these waves to the large-scale properties of the magnetic field. Near electron gyrofrequency harmonic emissions occur only when the ambient magnetic field points to a narrow range of directions bounded by polar and azimuthal angular ranges in the RTN coordinate system of correspondingly 80° ≲ θB ≲ 100° and 10° ≲ ϕB ≲ 30°. We show that the amplitudes of wave emissions are highest when both angles are close to the center of their respective angular interval favorable to wave emissions. The intensity of wave emissions correlates with the magnetic field angular changes at both large and small timescales. Wave emissions intervals correlate with intervals of decreases in the amplitudes of broadband magnetic fluctuations at low frequencies of 10–100 Hz. We discuss possible generation mechanisms of the waves.QC 20220831</p
    corecore