Revisiting the role of cosmic-ray driven Alfvén waves in pre-existing magnetohydrodynamic turbulence. I. Turbulent damping rates and feedback on background fluctuations

Abstract

Alfvén waves (AWs) excited by the cosmic-ray (CR) streaming instability (CRSI) are a fundamental ingredient for CR confinement. The effectiveness of self-confinement relies on a balance between CRSI growth rate and damping mechanisms acting on quasi-parallel AWs excited by CRs. One relevant mechanism is the so-called turbulent damping, in which an AW packet injected in pre-existing turbulence undergoes a cascade process due to its nonlinear interaction with fluctuations of the background. The turbulent damping of an AW packet in pre-existing magnetohydrodynamic turbulence is re-examined, revised, and extended to include most-recent theories of MHD turbulence that account for dynamic alignment and reconnection-mediated regime. The case in which the role of feedback of CR-driven AWs on pre-existing turbulence is important will also be discussed. Particular attention is given to the nonlinearity parameter ${\chi }^w$ that estimates the strength of nonlinear interaction between CR-driven AWs and background fluctuations. We point out the difference between ${\chi }^w$ and ${\chi }^z$ that instead describes the strength of nonlinear interactions between pre-existing fluctuations. When ${\chi }^w$ is properly taken into account, one finds that (i) the turbulent damping rate of quasi-parallel AWs in anisotropic turbulence depends on the background-fluctuations' amplitude to the third power, hence is strongly suppressed, and (ii) the dependence on the AW's wavelength (and thus on the CR gyro-radius from which it is excited) is different from what has been previously obtained. Finally, (iii) when dynamic alignment of cascading fluctuations and the possibility of a reconnection-mediated range is included in the picture, the turbulent damping rate exhibits novel regimes and breaks. Finally, a criterion for CR-feedback is derived and simple phenomenological models of CR-modified turbulent scaling are provided.

arXiv commentfinal version after language and layout corrections (19 pages, 3 figures, 2 tables)

References in corpus (45)

• A weak turbulence theory for incompressible MHD
• Spectrum of magnetohydrodynamic turbulence
• The Anisotropy of MHD Alfvénic Turbulence
• Cosmic rays in galaxy clusters and their non-thermal emission
• Anisotropic scaling of magnetohydrodynamic turbulence
• Compressible Sub-Alfvenic MHD turbulence in Low-beta Plasmas
• Scattering of Cosmic Rays by Magnetohydrodynamic Interstellar Turbulence
• Spectral breaks as a signature of cosmic ray induced turbulence in the Galaxy
• Recent progress in astrophysical plasma turbulence from solar wind observations
• Cosmic Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic Field
• Turbulence and Particle Heating in Advection-Dominated Accretion Flows
• Phase Diagram for Magnetic Reconnection in Heliophysical, Astrophysical and Laboratory Plasmas
• Scattering of energetic particles by anisotropic magnetohydrodynamic turbulence with a Goldreich-Sridhar power spectrum
• The Anisotropy of Electron MHD Turbulence
• Power and spectral index anisotropy of the entire inertial range of turbulence in the fast solar wind
• Turbulence, magnetic fields and plasma physics in clusters of galaxies
• Wave damping by MHD turbulence and its effect upon cosmic ray propagation in the ISM
• The gamma-ray and neutrino sky: A consistent picture of Fermi-LAT, Milagro, and IceCube results
• Cosmic Ray Transport in the Galaxy: a Review
• Anisotropy of Alfvénic Turbulence in the Solar Wind and Numerical Simulations
• Astrophysical hydromagnetic turbulence
• Turbulence, Magnetic Reconnection in Turbulent Fluids and Energetic Particle Acceleration
• Disruption of sheetlike structures in Alfvénic turbulence by magnetic reconnection
• Magnetohydrodynamic turbulence mediated by reconnection
• Refined critical balance in strong Alfvenic turbulence
• Damping of Alfven waves by Turbulence and its Consequences: from Cosmic-Rays Streaming to Launching Winds
• Diffusion of cosmic rays in MHD turbulence with magnetic mirrors
• Critical Balance and the Physics of MHD Turbulence
• Local Anisotropy, Higher Order Statistics, and Turbulence Spectra
• Plasma turbulence in the interstellar medium
• Cosmic ray transport in large-amplitude turbulence with small-scale field reversals
• Measures of Three-Dimensional Anisotropy and Intermittency in Strong Alfvénic Turbulence
• Non-linear diffusion of cosmic rays escaping from supernova remnants - II. Hot ionized media
• Kinetic plasma turbulence: recent insights and open questions from 3D3V simulations
• On the Growth and Saturation of the Gyroresonant Streaming Instabilities
• The theory of cosmic-ray scattering on pre-existing MHD modes meets data
• Dynamical Effects of Cosmic Rays on the Medium Surrounding Their Sources
• Cosmic-ray generated bubbles around their sources
• Grammage of cosmic rays in the proximity of supernova remnants embedded in a partially ionized medium
• How it cramps the flow: three regimes for the saturation of parallel ion-beam instabilities
• Cosmic ray streaming in the turbulent interstellar medium
• On the background-gyroresonant character of the Bell instability
• Formation of the cosmic-ray halo: The role of nonlinear Landau damping
• Turbulent regimes in collisions of 3D Alfvén-wave packets
• Galactic cosmic ray transport in the absence of resonant scattering