Comparison of Collisionless Plasma Plume Expansions Under Different External Magnetic Fields

Three-dimensional (3-D), fully kinetic particle-in-cell (PIC) simulations using the CHAOS code are conducted to investigate the expansion dynamics of magnetized mesothermal plasma plumes under various magnetic field topologies. The simulations incorporate static magnetic fields, including divergent and axially uniform configurations, mapped onto the Electric Forest of Trees (E-FOT) grids in CHAOS to explore their effects on plasma plume collimation. This study examines the influence of field strength and topology on plume behavior by tracking the plume front’s time evolution, analyzing macroparameters across cross-sections, evaluating electron thermal energy losses, and characterizing non-Maxwellian electron velocity distribution functions (EVDFs). The study demonstrates that uniform magnetic fields with strengths exceeding 150 G significantly enhance plume collimation, resulting in plume front speeds at least one ion acoustic speed (1 cs0) higher than those observed in unmagnetized or diverging field cases. Additionally, improved collimation in uniform fields reduces electron thermal energy losses by 50% and 60% compared to the losses observed in diverging field and unmagnetized cases, respectively.