GEM: Energy Conversion Associated with Non-equilibrium Velocity Distribution Functions in Dayside Magnetopause Reconnection

Dayside magnetopause reconnection controls plasma and energy input into the magnetosphere from the solar wind. It is associated with significant plasma heating and particle acceleration, yet these processes are not well-understood. One reason is that energy conversion between work, internal energy, and heat is traditionally defined for Maxwellian distributions and measured with lower order moments of the velocity distribution function (VDF), but in collisionless plasmas, the VDFs frequently appear in a non-Maxwellian state. Such non-equilibrium distributions can be unstable to the generation of instabilities and plasma waves which affect the VDFs via self-consistent wave-particle interactions. This project investigates energy conversion associated with non-equilibrium VDFs, an important study for understanding and predicting space weather. The work supports an early career PI and a post-doc from an under-represented group in STEM. Undergraduate students will be mentored and outreach conducted through the annual Maryland Day event. This project aims to understand when and where, and how and how much, the energy conversion associated with non-equilibrium VDFs occurs during dayside magnetopause reconnection. Scientific questions: (1) When and where does energy conversion associated with non-equilibrium VDFs, as measured by the kinetic entropy, occur in different regions of 2.5-dimensional (2.5D) asymmetric magnetic reconnection, and what do they imply about the mechanisms of energy conversion? (2) What are the differences of energy conversion processes occurring for different conditions of guide field strengths and diamagnetic drift speeds in 2.5D asymmetric magnetic reconnection? (3) What are the differences of energy conversion processes occurring between 2.5D and 3D asymmetric reconnection? Methodology: Using particle-in-cell simulations, the team will analyze (1) the presence of wave activity, (2) whether VDFs evolve towards or away from Maxwellianity, and (3) the presence of chaotic motions. By comparing these results, they will find where higher order moments are participating in energy conversion and disentangle whether the waves are energizing particles or non-Maxwellian VDFs are generating waves. Using the time evolution of non-Maxwellianity to understand wave-particle interactions is a brand-new technique. The results will be compared to Magnetospheric Multiscale (MMS) observations. This project is directly relevant to the GEM Focus Group, “Magnetic Reconnection in the Age of the Heliophysics System Observatory”. 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.