微波等离子推力器圆柱谐振腔等离子体流的数值研究

Numerical Research of Plasma Flow in Cylindrical Resonant Cavity of Microwave Plasma Thruster

为了获得微波等离子推力器(MPT)圆柱形谐振腔小型化的设计参数,采用时域有限差分法(FDTD)求解Maxwell方程、有限体积法求解N-S方程、单温度局域热平衡模型求解等离子体数密度、温度等参数的全数值方法,对MPT圆柱形谐振腔在不同微波频率、相同谐振模式情况下的微波等离子体耦合流场进行了数值模拟计算。计算结果表明,提高微波频率可缩小圆柱形谐振腔尺寸。圆柱形谐振腔小型化后,在腔内压强一定的情况下,相应地工质气体的流量减小、消耗的微波功率减小,喷管喉径也减小、从而MPT的推力也减小,且不同微波频率、相同谐振模式情况下,腔内等离子体区温度、压强、电子数密度的变化规律相同。这些结论为今后MPT的小型化设计提供了理论依据。

Microwave plasma thruster (MPT) is an electro-thermal propulsive device. We are the first in China to study MPT. Our MPT consists of a microwave generator, a gas storing and supplying system, a resonant cavity and an accelerating nozzle. When the microwave discharge breaks down the gas in the resonant cavity, free-floating plasma is generated. Then the plasma exhausts from nozzle to produce thrust. The key parameters in designing a small MPT suitable for space application are the geometric parameters and electromagnetic distribution parameters of the small cylindrical cavity. In order to obtain these parameters, we use the finite-difference time-domain (FDTD) method to solve the Maxwell equations, use the finite-volume method to solve the N-S equations; and use the single temperature local thermal equilibrium model to solve plasma equations. The numerical simulation of the coupling flow field of microwave plasma within resonant cavity was discussed under the condition of different frequencies and the same resonant model. The results of numerical simulation are as follows: (1) When the resonant model is fixed, the size of MPT will decrease with the increase of the microwave frequency. (2) When the pressure in the cavity is fixed, the flow rate of gas, the microwave power and the throat of nozzle of MPT will all decrease with the decrease of the size of MPT, and the thrust of MPT is also decreased. (3) The distribution of the temperature, the pressure and the electronic density in resonant cavity will be invariable when the resonant model is fixed and the resonant frequency is different. These results can be used for miniaturization of MPT.