2017/08/31 by Mario Riquelme, Alvaro Osorio, Eliot Quataert · 1 citation
Physics and Astronomy · #Anisotropy #Atomic physics #Dust and Plasma Wave Phenomena #Electron #Instability #Ionosphere and magnetosphere dynamics #Kinetic energy #Magnetic field #Physics #Quantum mechanics #Scattering #Solar and Space Plasma Dynamics #Whistler #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/aa95ba
7 pages, 6 figures, accepted in The Astrophysical Journal
openalex created_date 2017/08/31 · arxiv created 2017/11/22 · openalex publication_date 2017/11/22 · arxiv updated 2017/12/06 · openalex updated_date 2026/08/05
Abstract We use 2D particle-in-cell simulations to study the effect of the saturated whistler instability on the viscous heating and nonthermal acceleration of electrons in a shearing, collisionless plasma with a growing magnetic field, <?CDATA \boldsymbolB?> . In this setup, an electron pressure anisotropy with <?CDATA p⊥ ,e\gt p| | ,e?> naturally arises due to the adiabatic invariance of the electron magnetic moment ( <?CDATA p| | ,e?> and <?CDATA p⊥ ,e?> are the pressures parallel and perpendicular to <?CDATA \boldsymbolB?> ). If the anisotropy is large enough, then the whistler instability arises, efficiently scattering the electrons and limiting <?CDATA \rmΔ pe?> ( <?CDATA ≡ p⊥ ,e-p| | ,e?> ). In this context, <?CDATA \rmΔ pe?> taps into the plasma velocity shear, producing electron heating by the so-called anisotropic viscosity. In our simulations, we permanently drive the growth of <?CDATA | \boldsymbolB| ?> by externally imposing a plasma shear, allowing us to self-consistently capture the long-term, saturated whistler instability evolution. We find that besides the viscous heating, the scattering by whistler modes can stochastically accelerate electrons to nonthermal energies. This acceleration is most prominent when initially <?CDATA β e∼ 1?> , gradually decreasing its efficiency for larger values of <?CDATA β e?> ( <?CDATA ≡ 8π pe/| \boldsymbolB| 2?> ). If initially <?CDATA β e∼ 1?> , then the final electron energy distribution can be approximately described by a thermal component, plus a power-law tail with a spectral index of ∼3.7. In these cases, the nonthermal tail accounts for <?CDATA ∼ 5 % ?> of the electrons and for <?CDATA ∼ 15 % ?> of their kinetic energy. We discuss the implications of our results for electron heating and acceleration in low-collisionality astrophysical environments, such as low-luminosity accretion flows.