ABSTRACT Turbulent highenergy astrophysical systems often feature asymmetric energy injection: for instance, Alfvén waves propagating from an accretion disc into its corona. Such systems are ‘imbalanced’: the energy fluxes parallel and antiparallel to the largescale magnetic field are unequal. In the past, numerical studies of imbalanced turbulence have focused on the magnetohydrodynamic regime. In this study, we investigate externally driven imbalanced turbulence in a collisionless, ultrarelativistically hot, magnetized pair plasma using 3D particleincell (PIC) simulations. We find that the injected electromagnetic momentum efficiently converts into plasma momentum, resulting in net motion along the background magnetic field with speeds up to a significant fraction of lightspeed. This discovery has important implications for the launching of accretion disc winds. We also find that although particle acceleration in imbalanced turbulence operates on a slower timescale than in balanced turbulence, it ultimately produces a powerlaw energy distribution similar to balanced turbulence. Our results have ramifications for black hole accretion disc coronae, winds, and jets.
Weak Alfvénic turbulence in relativistic plasmas.Part 2. current sheets and dissipation
Alfvén waves as excited in black hole accretion disks and neutron star magnetospheres are the building blocks of turbulence in relativistic, magnetized plasmas. A large reservoir of magnetic energy is available in these systems, such that the plasma can be heated significantly even in the weak turbulence regime. We perform highresolution threedimensional simulations of counterpropagating Alfvén waves, showing that an $E_{B_{\perp }}(k_{\perp }) \propto k_{\perp }^{2}$ energy spectrum develops as a result of the weak turbulence cascade in relativistic magnetohydrodynamics and its infinitely magnetized (forcefree) limit. The plasma turbulence ubiquitously generates current sheets, which act as locations where magnetic energy dissipates. We show that current sheets form as a natural result of nonlinear interactions between counterpropagating Alfvén waves. These current sheets form owing to the compression of elongated eddies, driven by the shear induced by growing higherorder modes, and undergo a thinning process until they breakup into smallscale turbulent structures. We explore the formation of current sheets both in overlapping waves and in localized wave packet collisions. The relativistic interaction of localized Alfvén waves induces both Alfvén waves and fast waves, and efficiently mediates the conversion and dissipation of electromagnetic energy in astrophysical systems. Plasma energization through reconnection in current more »
 Publication Date:
 NSFPAR ID:
 10332451
 Journal Name:
 Journal of Plasma Physics
 Volume:
 87
 Issue:
 5
 ISSN:
 00223778
 Sponsoring Org:
 National Science Foundation
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