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Enhancement of the Nonresonant Streaming Instability by Particle Collisions
A Marret1,2,3, A Ciardi1, R Smets2
1Sorbonne Université, Observatoire de Paris, Université PSL, CNRS, LERMA, F-75005 Paris, France.
Physical Review Letters
|April 1, 2022
Summary
Cosmic rays can amplify magnetic fields through instabilities. In fully ionized plasmas, Coulomb collisions enhance this magnetic field amplification by suppressing pressure anisotropies, contrary to expectations for poorly ionized plasmas.
Area of Science:
- Plasma Physics
- Astrophysics
- Computational Physics
Background:
- Streaming cosmic rays are crucial for generating and amplifying magnetic fields in astrophysical environments.
- Turbulent magnetic fields are essential for confining and accelerating cosmic rays at shock fronts.
- The nonresonant instability driven by cosmic rays is a proposed mechanism for magnetic field growth.
Purpose of the Study:
- To investigate the role of particle collisions in the nonresonant cosmic ray instability.
- To explore the interplay between pressure anisotropies and collisions in magnetized plasmas.
- To understand magnetic field amplification in both poorly and fully ionized plasmas.
Main Methods:
- Hybrid-particle-in-cell simulations incorporating Monte Carlo collisions.
- Modeling of both poorly ionized and fully ionized plasma conditions.
- Analysis of pressure anisotropies and their interaction with particle collisions.
Main Results:
- Proton-neutral collisions rapidly damp the instability in poorly ionized plasmas, consistent with fluid theory.
- Coulomb collisions in fully ionized plasmas do not inhibit magnetic field growth.
- Coulomb collisions can suppress pressure anisotropies and enhance magnetic field amplification under specific conditions.
Conclusions:
- Particle collisions have a differential impact on cosmic ray-driven magnetic instabilities depending on plasma ionization.
- The nonresonant instability and subsequent magnetic field amplification can be enhanced in fully ionized astrophysical plasmas.
- These findings have implications for understanding magnetic field evolution in cosmic ray-affected environments.
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