感应式脉冲推力器中等离子体加速数值研究

为了分析感应式脉冲放电等离子体推力器中时变电磁场作用下等离子体的放电参数分布及其随着磁场强度变化的影响,引入了利用双曲型散度清除方法的二维轴对称瞬态等离子体流动的磁流体力学数值模型.计算结果表明,随着输入能量的增加,等离子体团出现速度峰值的时刻提前,等离子体中同时存在的异号电流环对其加速具有阻滞作用.等离子体的加速效率随着磁场强度非线性增大,磁场大于某一临界值时(几何构型下峰值磁场强度大于0.45 T),有限空间情况下等离子体的加速效率获得显著提高.

Numerical investigation on the plasma acceleration of the inductive pulsed plasma thruster

The pulsed inductive discharge ionizes the neutral gas and accelerates the plasma efficiently, and is accompanied by complicated phenomena during the discharge process. In order to study the transient flow field characteristics and the variations of the main flow parameters (e.g., velocity, density, pressure, etc.) with the magnetic induction intensity of the inductive pulsed plasma, the two-dimensional axisymmetric unsteady magnetohydrodynamic numerical model is introduced by employing the hyperbolic divergence cleaning method. The plasma is excited by the single pulse energy varying in the sine waveform with a period of 10 μs, and the flow field of the peak magnetic induction intensity ranging from 0.1 T to 0.55 T, is calculated. The results show that the high density and speed region gradually moves forward and away from the coil, leaving the low density and speed plasma behind, meanwhile, the high temperature region is near the coil throughoutthe discharge, and the inductive magnetic field leads in the phase, compared with the flow parameters, which indicates the effective permeation of the pulsed energy into the neutral gas and the plasma. As the input single pulse energy increases, the maximum axial velocity of the plasma increases and the time at which the flow velocity reaches a peak value moves up. The current sheets of the same direction, which are located on the surface of the induction coil at the beginning, appear as the discharge initiates and moves forward with the influenced flow domain expanding as the process goes on, and an opposite sign current sheet grows when the time passes through the first quarter of the sine period, which is also near the surface of the coil and heats the low-density plasma and the neutral gas. The opposite direction current sheets slow down the velocity of the plasmoid. Due to the nonlinear property of the coil-plasma interaction, the acceleration efficiency of the induction coil improves irregularly as the magnetic induction intensity increases, which grows slowly at a low level, and when the intensity reaches a certain critical value, for the configuration studied in this work the particular value is 0.45 T, the acceleration efficiency increases significantly, indicating that a larger part of the pulsed energy is converted into the plasma kinetic energy.