Modeling the Saturation of the Bell Instability using Hybrid Simulations

• DOI: 10.48550/arxiv.2210.08072
• Publication Date: 2024-05-01
• Authors: Georgios Zacharegkas; Damiano Caprioli; Colby Haggerty; Siddhartha Gupta; Benedikt Schroer
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); FOS: Physical sciences; Cosmic ray sources; Galactic cosmic rays; Astrophysics; 01 natural sciences; 7. Clean energy; Physics - Plasma Physics; QB460-466; Plasma Physics (physics.plasm-ph); High-energy cosmic radiation; 0103 physical sciences; Particle astrophysics; Astrophysics - High Energy Astrophysical Phenomena; Cosmic rays; High energy astrophysics

Abstract The nonresonant streaming instability (Bell instability) plays a pivotal role in the acceleration and confinement of cosmic rays (CRs), yet the exact mechanism responsible for its saturation and the magnitude of the final amplified magnetic field have not been assessed from first principles. Using a survey of hybrid simulations (with kinetic ions and fluid electrons), we study the evolution of the Bell instability as a function of the parameters of the CR population. We find that at saturation, the magnetic pressure in the amplified field is comparable with the initial CR anisotropic pressure, rather than with the CR energy flux, as previously argued. These results provide a predictive prescription for the total magnetic field amplification expected in the many astrophysical environments where the Bell instability is important.