Kinetic Center Journal Club presents "3D PIC Simulations of Particle Acceleration in Relativistic Jets with Helical Magnetic Fields"

 
One of the key questions in the study of relativistic jets is how magnetic reconnection occurs and whether it can effectively accelerate electrons in the jet. We performed 3D particle-in-cell (PIC) simulations of a
relativistic pair and electron-proton jet of relatively large radius that carries a helical magnetic field. We focused our investigation on the interaction between the jet and the ambient plasma and explore how the
helical magnetic field affects the excitation of kinetic instabilities such as the Weibel instability (WI), the kinetic Kelvin–Helmholtz instability (kKHI), and the mushroom instability (MI). In our simulations these kinetic instabilities are indeed excited, and particles are accelerated. At the linear stage of electron-proton jet case we observe recollimation shocks near the center of the jet. As the electron–proton jet evolves into the deep nonlinear stage, the helical magnetic field becomes untangled due to reconnection-like phenomena, and electrons are repeatedly accelerated as they encounter magnetic-reconnection events in the turbulent magnetic field. For the pair jet, kinetic instabilities (MI and kKHI), excited at the linear stage, generate a
quasi-steady x-component of electric field which accelerates and decelerates electrons. We find that withinthe pair jet, two concentric modes of mushroom instability (MI) are excited radially to the jet direction. In the
nonlinear stage the magnetic field generated by these instabilities becomes dissipated and reorganized into a new topology. These outer and inner MI modes dissipate at different locations in the nonlinear stage. At
the nonlinear stage the 3-dimensional magnetic field topology indicates possible reconnection sites. The accelerated particles in the linear stage are further accelerated by dissipation of magnetic field and/or reconnection, shedding further light on the nature of relativistic jet phenomena applicable to high-energy astrophysical environments such as Active Galactic Nuclei jets and Gamma-ray bursts.