Kinetic heating by Alfvén waves in magnetic shears

Francesco Pucci

In order to efficiently convert AW energy into particle energy, the original fluctuation must decay from the initial macroscopic (fluid) scale to smaller (kinetic) scales. It is widely accepted that this decay can be efficiently promoted by the interaction of counter-propagating AWs, leading to turbulence. However, when the magnetic field through which an AW propagates is inhomogeneous, the wave decay can be directly mediated by the interaction of the initial large-scale fluctuation with the background medium. In this work, we present the results of a numerical experiment in which the decay of AWs into KAWs in a magnetic shear is studied self-consistently in a range that goes from fluid to kinetic electron scales. We show how the AW-to-KAW transition, promoted by the inhomogeneous background, leads to differential heating for ions and electrons. This differential heating is justified via a simple argument on how the two species can access the kinetic and magnetic energy carried by AWs.