Small-scale turbulence and energy conversion in kinetic plasmas

Abstract:

A wide range of space and astrophysical environments host turbulent, magnetised plasmas. Understanding the properties of turbulent fluctuations and the mechanisms underlying their transfer through scales and dissipation is crucial to understand how turbulence feeds back on the macro-scale evolution and energetics of these systems. In this context, space plasmas are probably the best laboratory for the study of plasma turbulence. Over the past decades, in-situ measurements from space missions have indeed uncovered a complex scenario whereby several collisionless plasma processes may be simultaneously at play along the turbulent cascade (e.g., from magnetic reconnection to wave-particle interaction and cascades in velocity space). In this context, a long-lasting debate concerns the nature of the fluctuations at sub-ion scales, as well as the fundamental processes responsible for their scale-to-scale transfer and for their conversion into heat.

In the present talk, recent advances in understanding sub-ion-range turbulence and turbulent heating that have been achieved with 3D simulations are discussed. After a first part focusing on gyro-fluid studies of interactions between kinetic-Alfvén-wave (KAW) packets as possible building blocks of the kinetic-range cascade[1], special emphasis will be put on a hybrid-kinetic approach to the MHD-to-kinetic transition. This includes studies of the spectral properties of electromagnetic fluctuations[2,3], of the anisotropic cascade of ion-entropy fluctuations that involves the whole six-dimensional phase space[4], and of the relevant ion-heating mechanisms[5].

[1] Cerri, Passot, Laveder, Sulem, Kunz, J. Plasma Phys. (in preparation)
[2] Cerri, Servidio & Califano, Astrophys. J. Lett. 846, L18 (2017)
[3] Cerri, Groselj & Franci, Front. Astron. Space Sci. 6, 64 (2019)
[4] Cerri, Kunz & Califano, Astrophys. J. Lett. 856, L13 (2018)
[5] Cerri, Arzamasskiy, Kunz, Chandran, Astrophys. J. (to be submitted)