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在9种等离子体击穿温度下,数值模拟了二次反射式聚焦系统聚焦情况下激光推力器内流场的演化过程,得到了不同击穿温度对应的能量沉积率、推力峰值、冲量和冲量耦合系数,能量沉积率和推进性能参数在某个等离子体击穿温度值处发生突变。根据空气对激光的逆韧致吸收系数公式,计算了CO2激光辐照下不同等离子体击穿温度对应的空气辐射自由程,发现当等离子体击穿温度为14000K时,辐射自由程为1.4mm,与计算网格的典型尺寸相当,此时入射激光能量在一个网格内以一定效率被吸收,由此确定了基于逆韧致吸收的激光等离子体的击穿温度。
The numerical simulation of the evolution of the flow field in the laser thruster under the condition of focusing of the secondary reflection system was carried out at nine kinds of plasma breakdown temperatures. The energy deposition rate, thrust peak, impulse and impulse Coupling coefficients, energy deposition rates, and propulsion performance parameters change abruptly at a plasma breakdown temperature. According to the formula of inverse toughness absorption coefficient of air to laser, the free path of air radiated by different plasma breakdown temperature under CO2 laser irradiation was calculated. It was found that when the plasma breakdown temperature is 14000K, the free radiation path is 1.4mm, Corresponds to the typical size of the computational grid, at which point the incident laser energy is absorbed with a certain efficiency within a grid, thereby determining the breakdown temperature of the laser plasma based on the reverse osmosis absorption.