Numerical Studies of Filamentary Plasma Structure in Microwave Rocket

摘要

High power millimeter-wave discharge in atmospheric air is characterized by filamentary structure and supersonic propagation of the ionization front, driving a Shockwave. In this research, the plasma structure was studied experimentally, using a 170 GHz gyrotron at power range of 200 kW to 700 kW, and numerically. About the ionization front propagation process, it is important to investigate steady plasma formation process, in a filamentary form, through millimeter wave. Each filamentary element is formed by granular plasmoids which are not propagating along or perpendicular to the electric field, but propagating into the wave source. To solve this mechanism, 2D numerical simulations was conducted using plasma fluid model. In dozens of times the size of plasma element scale, the steady plasma structure formation was simulated, and the calculation results were compared with previous experimental results. The calculated formation patterns were in good qualitative agreement with experiments. Thus, the simulation model provides a new physical interpretation of the pattern formation and dynamics in undercritical breakdown conditions. This causes the change of characteristic in the ionization front velocity deduced from the "theoretical speed". Thus, in the low power density experimental condition, the plasma structure is different from that in high power density condition.