MHD modeling of magneto-deflagration and magneto-detonation modes of air plasma jets in coaxial plasma accelerators in VLEO

Gas-fed coaxial plasma accelerators exhibit distinct magnetohydrodynamic (MHD) discharge modes, yet the gas-field coupling governing their formation and evolution under very low Earth orbit (VLEO) relevant conditions using air as the propellant is not fully characterized. These discharge modes dictate plume morphology and dynamics, influencing downstream flow characteristics. Understanding the structure of MHD flows has applications in increasing specific impulse and propellant utilization in electromagnetic thrusters, as well as in understanding the origin of astrophysical flows. This study employs 2D resistive MHD modeling to investigate how gas-loading conditions influence the establishment and subsequent evolution of MHD regimes, and how these evolving modes affect plasma dynamics and structure in coaxial plasma thrusters under VLEO-relevant conditions. The numerical framework adopts a validated plasma–vacuum interface tracking algorithm, ensuring a physically consistent representation of magnetized air plasma jet expansion into a vacuum, which is essential for capturing the magneto-deflagration MHD mode. Simulation results are compared with experimental observations of broadband plasma structure, exhaust velocity, and impulse bit, demonstrating agreement. In magneto-deflagration mode, efficient conversion of input energy into directed kinetic energy yields high exit velocities (∼65 km/s) and impulse bits; in magneto-detonation regime, shock-related thermal dissipation reduces exit velocities (∼30 km/s) and impulse bits. A sensitivity analysis identified inlet temperature as the dominant factor affecting impulse bit. Overall, simulation findings showed the dependence of MHD regimes on initial gas-loading profiles, identified transition behavior associated with their onset and evolution, and predicted the resulting transformations in plume structure and dynamics.