Science goals and objectives collisionless shocks are ubiquitous in space and astrophysical plasmas. They are an extremely important physical phenomenon: they dissipate kinetic energy into heat,…

This is a $555,000 research grant awarded to the University of Chicago by the National Aeronautics and Space Administration (NASA) under Contract #80NSSC18K1218. The grant funds a study on the physics of collisionless shocks in space and astrophysical plasmas, including how shocks generate energetic particles and magnetic turbulence. The research will utilize data from NASA's WIND, THEMIS, and MMS spacecraft missions, along with advanced kinetic plasma simulations, to better understand the processes leading to particle acceleration and the overall dynamics of collisionless shocks. This work has implications for understanding solar energetic particle generation, which is critical for space weather monitoring and mitigation. The grant does not have a set-aside designation, reflecting the University of Chicago's status as a major research institution. NASA is the funding agency for this grant.

Science goals and objectives collisionless shocks are ubiquitous in space and astrophysical plasmas. They are an extremely important physical phenomenon: they dissipate kinetic energy into heat, produce energetic particles, and generate magnetic turbulence. Astrophysical shocks are also prominent sources of high-energy cosmic rays, and produce non-thermal emission spanning from radio to gamma-RAY bands. In-situ observations of non-thermal particles associated with heliospheric shocks provide a unique opportunity to investigate the processes that lead to particle energization along with the underlying electromagnetic structure of collisionless shocks. Such a structure arises from the non-linear interplay between particles (both thermal and accelerated) and magnetic fluctuations, which can only be properly modeled via kinetic plasma simulations. Examples of the questions we will address are: 1) how do shocks generate the distributions of energetic ions and electrons they are often associated with? 2) how are upstream shocklets and short large-amplitude magnetic structures (slams) formed? How are ions and electrons accelerated in such foreshock disturbances? Can standard acceleration mechanisms account for the relativistic particles recently detected in such environments (wilson ET AL., PRL, 2016)? 3) how do non-maxwellian tails impact the macro- and microscopic shock dynamics? 4) how does the acceleration of electrons and ions depend upon the shock parameters (e.g., shock sonic and magnetosonic mach numbers, angle between shock normal and background magnetic field)? 5) what is the role of pre-existing energetic particles and density/magnetic field fluctuations? The proposed work will significantly improve our present understanding of energetic particle production and transport in the heliosphere, and in particular at the terrestrial BOW shock and at interplanetary shocks near 1 AU. We will construct a quantitative and unified picture of collisionless shock dynamics, including non-thermal electrons, protons, alpha particles, and heavier ions. Our work will significantly enhance our understanding of solar energetic particle generation mechanisms, which is critical to space system designers and operators. Proposed methodology we propose to exploit the high time, energy, and angular resolution of the wind, themis, and MMS spacecraft instrument suites in order to characterize the populations of accelerated particles at heliospheric shocks as a function of shock and plasma parameters, and compare spacecraft observations with synthetic particle spectra obtained via state-of-the-art kinetic simulations. We will use both full particle-in-cells (PIC) and hybrid simulations (fluid electrons/kinetic protons) to study particle thermalization, injection, transport, and acceleration, with particular attention to the mechanisms responsible for the formation of foreshock disturbances and for particle energization in slams, foreshock bubbles, and hot-flow anomalies. Hybrid simulations allow for a full characterization of the ION dynamics, and on modern supercomputers can cover scales comparable with the earth s BOW shock. They can handle multiple ION species, so that we will investigate the thermalization and energization of protons, alpha particles, and heavier ions with arbitrary mass/charge ratio. PIC simulations can also account for electron acceleration, and will be crucial especially for investigating the recent discovery of transrelativistic electrons in foreshock disturbances. PI caprioli is an expert of kinetic simulations of non-relativistic shocks, and will perform the numerical investigation of the parameter space relevant for heliospheric shocks. CO-i wilson is the wind spacecraft project scientist, has significant expertise in working with the wind and themis spacecraft, and will be in charge of selecting and analyzing spacecraft data to be compared with simulation outputs.