Quasi-cylindrical kinetic simulations of particle acceleration driven by the kink instability in relativistic magnetized jets

Relativistic magnetized jets from active galactic nuclei (AGNs) are powerful sources of non-thermal particles and radiation, but their particle acceleration mechanisms remain poorly understood. Recent kinetic simulations have shown that both current and pressure-driven hydromagnetic instabilities in the jet can result in efficient conversion of magnetic energy into non-thermal particles. However, these simulations are computationally expensive as they need to capture large scale separations between the (kinetic) gyro radius scales of thermal particles and the macroscopic jet radius, to understand the scaling properties of these acceleration mechanisms and their implications for astrophysically relevant system sizes.

Here, we explore the potential of PIC simulations in a quasi-cylindrical (‘quasi-3D’) geometry, where fields and currents are decomposed in a truncated azimuthal basis, to carry out high dynamic range studies of particle acceleration in relativistic jets. We validate quasi-3D simulations against full cartesian 3D simulations of non-thermal particle acceleration driven by the MHD kink instability in force-free and pressure-balanced equilibria. We discuss how restricting the number of azimuthal modes impacts the particle acceleration physics in different initial configurations, and offers new insights into the importance of small-scale field fluctuations (associated with high azimuthal mode numbers) on the efficiency of particle acceleration. We conclude that quasi-3D PIC simulations offer a viable and computationally efficient method of probing the 3D physics of particle acceleration in relativistic jets.