FG: Particle Heating and Thermalization in Collisionless Shocks in the MMS Era

Focus Group Chairs

1. Lynn Wilson, NASA Goddard Space Flight Center (lynn.b.wilsoniii@gmail.com)
2. Li-Jen Chen, Astronomy Department, University of Maryland, College Park (lijen@mailaps.org)
3. Katherine Goodrich, Space Sciences Laboratory, University of California at Berkeley (katygoodrich@berkeley.edu)
4. Ivan Vasko, Space Sciences Laboratory, University of California at Berkeley (ivan.vasko@ssl.berkeley.edu)

Term: Five years (2019-2024)

Introduction to the focus group

Topic

Particle heating and thermalization in collisionless shocks are important unsolved problems, because of the challenges to resolve the kinetic scales with past in-situ data and simulations. Further progress in modeling collisionless shocks and validating MHD, hybrid, and PIC simulations requires resolving particle heating and thermalization processes from the ion to electron kinetic scales. Understanding these processes to the level with predictive capabilities will advance simulations of collisionless shock waves and wave-particle interactions, whether occurring near-Earth or other regions of space. The broad goals of the FG are to address (1) the structure of the quasi-static electric fields in collisionless shocks and their role in particle heating, (2) waves/structures in collisionless shocks and their generation mechanisms, (3) contributions of quasi-static and high-frequency electric fields to particle heating and thermalization and (4) enabling advances of MHD, hybrid, and PIC simulations to model the Earth’s bow shock and magnetosheath plasma. We expect to have strong collaborations with other focus groups that study the phenomena sensitive to the solar wind input.

The major focus of the Focus Group is particle heating and thermalization processes in collisionless shocks at kinetic scales, through the Earth’s bow shock and interplanetary shock observations and modern numerical simulations. Understanding and modeling these fundamental processes are essential to modeling geospace as the bow shock controls the solar wind input into the magnetosphere. The proposed FG will primarily build on the synergy of the unprecedented observation and modeling capabilities that have only come into effect in the past few years.

Goals & Deliverables

The broad goal of the Focus Group is to:

• establish the distribution and properties of the quasi-static electric field in collisionless shocks, resolve particle heating by the quasi-static field, quantitatively compare terms in Ohm’s law;
• analyze microscopic fluctuations (small-scale & high-frequency electric and magnetic fields) across subcritical and supercritical shock waves: census of waves/structures contributing to the microscopic fluctuations; mechanisms of fluctuation generation;
• establish contributions of quasi-static and high frequency fields in particle heating and thermalization in collisionless shocks; and
• establish the limits of applicability of existing MHD, hybrid, and PIC simulations of collisionless shocks to improve simulations of the terrestrial bow shock to accurately reproduce the plasma properties of the magnetosheath.

The deliverables include:

• quantify the contributions of macro- and microscopic fields in particle heating and thermalization at the terrestrial bow shock;
• quantify constraints and limits of applicability of existing simulations of collisionless shocks; and
• quantified constraints will motivate improvements for MHD, hybrid, and PIC simulations with the goal of reproducing the microscopic processes in the sheath downstream of collisionless shocks.