Plasma and Electric Property Analysis together with Resonance Regulation Experiment of MPT on TM<sub>011</sub> Mode

Microwave plasma thruster (MPT) is one type of electrothermal thruster, inside of which the plasma can be formed through gas heating by microwave energy and accelerated by nozzle to generate thrust. According to the different principle and operating procedure, the specific impulse of MPT is higher than that of chemical thruster and lower than that of magnetic confinement ion and Hull thruster, however the thrust of MPT is higher than that of magnetic confinement ion and Hull thruster and lower than that of chemical thruster. Therefore MPT possesses the excellent qualities of chemical and electric thruster, which will make it has the possibility of applying in space. Inside of the MPT cylindrical cavity, plasma changing procedure and microwave electric field distribution together with TM₀₁₁ resonant state influence the thruster performance seriously. According to the previous MPT formed through continuous regulation on the resonant sate of cylindrical cavity, it is needed to research a newly fixed and simple MPT, which will simplify the resonant state regulation and provide important basement for further study. Therefore the plasma procedure is analysis to find the best gas discharge condition, otherwise the microwave electric field intensity and power density distribution inside of the cavity running on TM₀₁₁ resonant sate is calculated to analyse how the parameters is influenced by the cavity dimensions. The resonant state is finely regulated to study how it is influenced by the dimension of cylindrical cavity and microwave coupling probe with ball and half ball structure. The result of theoretical analysis and calculation shows that the lowest discharge power of helium gas is present at the condition of 489Pa and microwave electric density distribution inside of the cavity is beneficial as the ratio of length to diameter greater than 1. As the length and radius of microwave coupling ball probe is suitable, the experiment of resonant state regulation shows that the shortest cylinder cavity is on the best optimum resonant sate, and its resonant frequency is very near to 2.45GHz. The helium discharge experiment demonstrates that this shortest cavity matched by the suitable ball probe have the property of high microwave power utilizing and easy discharge of helium gas, which will make MPT operation reliably.