2025/11/06 by Ryan Golant, Luca Comisso, Golant, Ryan +5
Physics and Astronomy · #Astrophysics and Star Formation Studies #Dust and Plasma Wave Phenomena #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Solar and Space Plasma Dynamics
paper · pdf · doi:10.48550/arxiv.2511.04663
openalex publication_date 2025/11/06 · openalex created_date 2025/11/08 · openalex updated_date 2026/08/01
Large-amplitude turbulence -- characterized by a fluctuating magnetic field component, δB, that is stronger than the mean component, B0 -- is generically intermittent, populated with intense localized structures such as sharp field-line bends and rapid field reversals. Recent MHD simulations suggest that these structures play an important role in particle transport and acceleration; however, MHD is inapplicable in most of our Universe, where the plasma is so hot or diffuse that Coulomb collisions are negligible. Therefore, in this paper, we analyze the intermittent properties of collisionless large-amplitude turbulence in electron-positron plasmas via fully kinetic 3D simulations, exploring a wide range of δB / B0 and scale separations between the turbulence driving scale, L, and kinetic scales, c/ω\rm p. The steady-state collisionless turbulence in our simulations broadly resembles that of MHD, but the development of pressure anisotropy steepens the scaling between magnetic field strength, B, and scalar field-line curvature, K_∥ -- yielding B ∝ K_∥-3/4 -- and consequently modifies the power-law slope of the probability density function of K_∥; this slope hardens from K_∥-2.5 to K_∥-2.0 as δB / B0 increases from 4 to 140. Pressure anisotropy also triggers mirror and firehose instabilities, with the volume-filling fractions of these fluctuations increasing with δB / B0; for our largest δB / B0, 20% of the volume is mirror-unstable and 6% is firehose-unstable. Both the curvature and the Larmor-scale fluctuations in collisionless large-amplitude turbulence are expected to significantly influence cosmic ray transport and acceleration in the interstellar medium of our Galaxy and the intracluster medium of galaxy clusters.