Kinetic Studies of the Relativistic Pinch: A Key to Particle Acceleration in Astrophysical Plasmas

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Rapidly flaring gamma-rays and other radiative signals from blazar jets and pulsar wind nebulae indicate that standard models for energy dissipation and particle acceleration in relativistic cosmic plasmas, which invoke shock waves and hydromagnetic diffusion, are probably incorrect. This project uses powerful new computational tools to study a promising alternative: the direct dissipation of magnetic energy through reconnection and turbulence in collisionless relativistic plasmas. The study will explore relativistic particle acceleration and the associated radiation in a much more realistic astrophysical context than the idealized configurations used to obtain encouraging preliminary results. This work will yield insights into the interactions of black holes with their cosmic environments. The innovative approaches to PIC simulation can be applied to a broad range of problems in space physics and laboratory plasmas. There is a range of associated research experiences for undergraduates, as well as support, training and mentorship for a postdoctoral researcher. Contribution to public scientific literacy comes through collaboration with the Fiske Planetarium, using visually arresting graphics and animations from the simulations.Simulations which have started from idealized configurations have shown robust nonthermal particle energy distributions and variability characteristics. The particle distributions correlate with the initial magnetization of the plasma, which is the ratio of magnetic energy density to relativistic plasma enthalpy. Surprisingly, similar correlations develop in systems with different compositions (pairs or electron-ion plasma) and in setups ranging from idealized reconnecting current sheets to three-dimensional driven turbulence. A vertical kinetic study will follow unstable magneto-hydrodynamic pinch configurations through their nonlinear development to the resulting turbulence, reconnection, particle acceleration, and radiation. The well-tested Zeltron radiative Particle-in-Cell (PIC) code, developed by this team and publicly available since 2014, enables a thorough analysis of "kinetic beaming," and a study of the relationships between microscopic kinetic processes and macroscopic features such as secondary flux ropes, current sheets, and bulk flows. State-of-the-art computational tools allow kinetic and radiative plasma phenomena to be related to macroscopic magnetohydrodynamic instability, under relativistic conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.