Accelerazione di particelle in plasmi astrofisici

Particle acceleration in astrophysical plasmas is of crucial importance in order to understand the ultra high-energy emission from Active Galactic Nuclei and Gamma-Ray Bursts. Typically, acceleration can occur via the first- and second-order Fermi processes as well as magnetic reconnection events taking place in strongly magnetized current sheets. With the present work, I focus on the latter case, considering three cases of increasing complexity: single time-independent current sheet, single time-dependent current sheet that becomes unstable due to the development of the Tearing instability and multiple time-dependent current sheets formed as a byproduct of the Kelvin-Helmholtz (KH) instability, which develops at the jet/ambient interface. It is shown, by means of 2D numerical simulations of charged test particles coupled to a fluid with different magnetizations and velocities, that particles can be efficiently accelerated by repeated encounters with these dynamically evolving current-sheets.