Collaborative Research: Multidimensional Kinetic Simulations of Particle Acceleration in Astrophysical Collisionless Shocks

About This Grant

Collisionless shocks are ubiquitous in space and astrophysical plasmas: they dissipate kinetic energy into heat, produce energetic particles, and generate magnetic turbulence. Shock-accelerated particles are key for the non-thermal emission (from radio to gamma-ray bands to high-energy neutrinos) observed in many astrophysical objects and events, such as novae, supernovae, pulsar wind nebulae, clusters of galaxies, and winds and jets launched by active galactic nuclei. Shock acceleration is usually attributed to the first-order Fermi mechanism, involving particle scattering around two sides of the shock to gain energy. Despite its universality in astrophysics, the conditions for operation of this process, and particularly its efficiency, is not understood from first principles, as they depend on microscopic plasma physics of the shock transition. A research collaboration between Princeton University and the University of Chicago will address this problem from first principles by performing large-scale multidimensional kinetic particle-in-cell and hybrid simulations of astrophysical collisionless shocks and studying the development of self-consistent particle acceleration. The work will integrate research and education through the involvement of graduate and undergraduate students and postdocs. The students will be trained in numerical modeling of multiscale systems; this experience will prepare them for careers in science and technology fields, where large-scale computing increasingly plays an important role. The outreach efforts will engage public interest in plasma physics and astrophysics. The research program will answer several fundamental questions about shock acceleration: 1) how the acceleration efficiency of electrons and ions depends on shock parameters and dimensionality; 2) how the internal structure of a shock changes with magnetic turbulence generated by accelerated particles; 3) what are the proton and electron spectra generated at realistic astrophysical shocks? The researchers will develop parameterizations of the results of kinetic simulations for inclusion into a semi-analytical model of shock-accelerated spectra that will bridge the scales between microscopic shock physics and macroscopic emission modeling for astrophysical sources. The results of this research are also of broad significance to space physics, where particle acceleration in heliospheric shocks is observed in-situ by spacecraft. Collisionless shock physics is also being studied through laboratory experiments with intense lasers, and the findings of this research program will be relevant to the interpretation of shock experiments. 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.