In this study, the gas-species-dependence of plasma propagation was numerically investigated to maximize the thrust performance of a microwave rocket with a gas propellant tank. An external magnetic field was applied to the breakdown volume inside the rocket nozzle to suppress plasma propagation toward the exit of the nozzle. In the absence of the magnetic field, the speed of plasma propagation in argon was higher than that in nitrogen because of the smaller elastic collision frequency and faster electron diffusion. However, the relationship in terms of the speed of plasma propagation was reversed when the magnetic field was applied to the breakdown volume because of infrequent elastic collisions in argon. The speed of plasma propagation under the external magnetic field was theoretically modeled as 2 D ⊥ ν i and decreased with increasing value of the Hall parameter Ω in the region where Ω > 1. It is, therefore, better to use a gaseous propellant that incurs a small elastic collision frequency in the microwave rocket supported by an external magnetic field, because a larger value of Ω suppresses plasma propagation and yields a superior thrust performance.
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