Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Anomalous Proton Velocity Diffusion by Quasi-monochromatic Kinetic Alfvén Waves
Abstract The anomalous diffusion of resonant protons in parallel and perpendicular velocity space by kinetic Alfvén waves is discussed. The velocity diffusion coefficient is calculated by employing an autocorrelation function for proton trajectories. It is found that for protons resonant with the waves, the perpendicular diffusion coefficient decays away for a sufficiently long time, but parallel diffusion monotonically increases in time until it saturates at a certain level. This result indicates that a portion of resonant protons can undergo anomalous diffusion along the background magnetic field even if the intensity of the kinetic Alfvén wave is sufficiently low. The present findings imply that under suitable conditions, astrophysical charged-particle acceleration can take place in the parallel direction.  more » « less
Award ID(s):
1842643
PAR ID:
10325724
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
910
Issue:
2
ISSN:
0004-637X
Page Range / eLocation ID:
140
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT Ion beam-driven instabilities in a collisionless space plasma with low β, i.e. low plasma and magnetic pressure ratio, are investigated using particle-in-cell (PIC) simulations. Specifically, the effects of different ion drift velocities on the development of Buneman and resonant electromagnetic (EM) right-handed (RH) ion beam instabilities are studied. Our simulations reveal that both instabilities can be driven when the ion beam drift exceeds the theoretical thresholds. The Buneman instability, which is weakly triggered initially, dissipates only a small fraction of the kinetic energy of the ion beam while causing significant electron heating, owing to the small electron-ion mass ratio. However, we find that the ion beam-driven Buneman instability is quenched effectively by the resonant EM RH ion beam instability. Instead, the resonant EM RH ion beam instability dominates when the ion drift velocity is larger than the Alfvén speed, leading to the generation of RH Alfvén waves and RH whistler waves. We find that the intensity of Alfvén waves decreases with decrease of ion beam drift velocity, while the intensity of whistler waves increases. Our results provide new insights into the complex interplay between ion beams and plasma instabilities in low β collisionless space plasmas. 
    more » « less
  2. ; ; ; ; (, Astronomy & Astrophysics)
    Context.The heating of the solar corona and solar wind, particularly through suprathermal particles and kinetic Alfvén waves (KAWs) within the 0–10 RSunrange, has been a subject of great interest for many decades. This study investigates and explores the acceleration and heating of charged particles and the role of KAWs in the solar corona. Aims.We investigate how KAWs transport energy and accelerate and heat the charged particles, focusing on the behavior of perturbed electromagnetic (EM) fields, the Poynting flux vectors, net power transfer through the solar flux loop tubes, resonant particles’ speed, group speed, and the damping length of KAWs. The study examines how these elements are influenced by suprathermal particles (κ) and the electron-to-ion temperature ratios (Te/Ti). Methods.We used kinetic plasma theory coupled with the Vlasov-Maxwell model to investigate the dynamics of KAWs and particles. We assumed a collisionless, homogeneous, and low-beta electron-ion plasma in which Alfvén waves travel in the kinetic limits; that is,me/mi ≪ β ≪ 1. Furthermore, the plasma incorporates suprathermal high-energy particles, necessitating an appropriate distribution function to accurately describe the system. We adopted the Kappa distribution function as the most suitable choice for our analysis. Results.The results show that the perturbed EM fields are significantly influenced byκand the effect of Te/Ti. We evaluate both the parallel and perpendicular Poynting fluxes and find that the parallel Poynting flux (Sz) dissipates gradually for lowerκvalues. In contrast, the perpendicular flux (Sx) dissipates quickly over shorter distances. Power deposition in solar flux tubes is significantly influenced byκand Te/Ti. We find that particles can heat the solar corona over long distances (RSun) in the parallel direction and short distances in the perpendicular direction. The group velocity of KAWs increases for lowerκvalues, and the damping length, LG, is enhanced under lowerκ, suggesting longer energy transport distances (RSun). These findings offer a comprehensive understanding of particle-wave interactions in the solar corona and wind, with potential applications for missions such as the Parker Solar Probe, (PSP), and can also apply to other environments where non-Maxwellian particle distributions are frequently observed. 
    more » « less
  3. ; ; (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT We investigate the possibility of cosmic ray (CR) confinement by charged dust grains through resonant drag instabilities (RDIs). We perform magnetohydrodynamic particle-in-cell simulations of magnetized gas mixed with charged dust and cosmic rays, with the gyro-radii of dust and GeV CRs on ∼au scales fully resolved. As a first study, we focus on one type of RDI wherein charged grains drift super-Alfvénically, with Lorentz forces strongly dominating over drag forces. Dust grains are unstable to the RDIs and form concentrated columns and sheets, whose scale grows until saturating at the simulation box size. Initially perfectly streaming CRs are strongly scattered by RDI-excited Alfvén waves, with the growth rate of the CR perpendicular velocity components equaling the growth rate of magnetic field perturbations. These rates are well-predicted by analytic linear theory. CRs finally become isotropized and drift at least at ∼vA by unidirectional Alfvén waves excited by the RDIs, with a uniform distribution of the pitch angle cosine μ and a flat profile of the CR pitch angle diffusion coefficient Dμμ around μ = 0, without the ‘90○ pitch angle problem.’ With CR feedback on the gas included, Dμμ decreases by a factor of a few, indicating a lower CR scattering rate, because the backreaction on the RDI from the CR pressure adds extra wave damping, leading to lower quasi-steady-state scattering rates. Our study demonstrates that the dust-induced CR confinement can be very important under certain conditions, e.g. the dusty circumgalactic medium around quasars or superluminous galaxies. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, The Astrophysical Journal Letters)
    We investigate energetic particle diffusion in the inner heliosphere (0.06–0.3 au) explored by Parker Solar Probe (PSP). Parallel and perpendicular diffusion coefficients are calculated using second-order quasi-linear theory (SOQLT) and unified nonlinear transport theory, respectively. PSP’s in situ measurements of magnetic turbulence spectra, including sub-Alfvénic solar wind, are decomposed into parallel and perpendicular wavenumber spectra via a composite two-component turbulence model. These spectra are then used to compute parallel and perpendicular diffusion coefficients across energies ranging from sub-GeV to GeV. Our results reveal a strong energy and radial distance dependence in parallel diffusion coefficient. While perpendicular diffusion coefficient remains much smaller, it can rise accordingly in regions with relatively high turbulence levels. To validate our results, we estimate parallel diffusion using an upstream time-intensity profile of a solar energetic particle event observed by the PSP and compare it with theoretical values from different diffusion models. Our results suggest that the SOQLT-calculated parallel diffusion generally shows better agreement with solar energetic particle intensity-derived estimates than the classic quasi-linear theory model. This indicates that the SOQLT framework, which incorporates resonance broadening and nonlinear corrections and does not require the introduction of an ad hoc pitch-angle cutoff, may provide a more physically motivated description of energetic particle diffusion near the Sun. 
    more » « less
  5. ; ; (, Physics of Plasmas)
    The linear stability of waves driven by ion beams produced during solar flare energy release are explored to assess their role in driving abundance enhancements in minority species such as 3He and in controlling, through pitch-angle scattering, proton/alpha confinement during energy release. The Arbitrary Linear Plasma Solver is used to solve the linear dispersion relation for a population of energetic, reconnection-accelerated protons streaming through a less energetic background plasma. We assume equal densities of the two populations, using an anisotropic (T∥/T⊥=10), one-sided kappa distribution for the energetic streaming population and a cold Maxwellian for the background. We find two unstable modes with parallel propagation: a right-handed wave with a frequency of the order of the proton cyclotron frequency (Ωcp) and a left-handed, lower frequency mode. We also find highly oblique modes with frequencies below Ωcp that are unstable for higher beam energies. Through resonant interactions, all three modes will contribute to the scattering of the high-energy protons, thereby limiting their transport out of the flare-acceleration region. The higher-frequency oblique mode, which can be characterized as a kinetic Alfvén wave, will preferentially heat 3He, making it a good candidate for the driver of the abundance enhancements commonly observed for this species in impulsive events. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email