Proton acceleration by kinetic turbulence across various magnetization levels in astrophysical plasmas

Turbulence in astrophysical plasma transfers energy to kinetic scales, leading to proton acceleration or heating, yet the formation of suprathermal protons from such turbulence is not fully understood. While proton acceleration modeling based on the Fokker-Planck equation with diffusion through kinetic Alfvén waves (KAW) has been proposed to understand in-situ measurements of suprathermal protons in the interplanetary medium, more investigations using such modeling could help clarify the nature of particle acceleration in various astrophysical media beyond the interplanetary medium. Since the characteristics of KAW turbulence depend on the magnetization of the plasma system and the temperature anisotropy of the proton distribution function, proton acceleration mediated by KAW turbulence could also be influenced by these factors. By solving the Fokker-Planck equation, this study examines proton acceleration through KAW turbulence across strongly to weakly magnetized astrophysical plasmas, parameterized by plasma beta (β=0.01−10\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\beta =0.01-10$\end{document}), and the effects of proton temperature anisotropy. Particularly, our findings indicate that KAW turbulence significantly influences the presence of suprathermal protons in low-beta plasmas, such as the interplanetary medium, but is less impactful in high-beta environments, like the intergalactic and intracluster medium. Additionally, the proton temperature anisotropy significantly modulates the efficiency of proton diffusion in velocity space in low-beta environments.