激光推进辐射击穿温度特性的数值研究

Numerical study on laser breakdown temperature in radiation gas-dynamics computation for laser propulsion

关键词:  激光推进  逆韧致吸收  激光等离子体  击穿温度  辐射自由程

Key words:  Laser propulsion  Inverse bremsstrahlung absorption  Laser plasma  Breakdown temperature  Radiative free path

摘要:

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。

Abstract:

Under nine plasma breakdown temperature, inner fluid flow evolvement process of laser thruster is simulated numerically when laser is focused by two-reflective focusing system. Laser deposit efficiency, thrust peak value, impulse and impulse coupling coefficient are obtained. Laser deposit efficiency and propulsive performance parameters varied suddenly at a certain plasma breakdown temperature. Based on the formula of inverse bremsstrahlung absorption coefficient, radiative free path of air at different plasma breakdown temperature under irradiation of CO2 laser are calculated. When plasma breakdown temperature is 14 000 K, the radiative free path of air is 1.4 mm, which is comparable to typical size of computational grid, and the incident laser energy is absorbed in one grid by some percent. Therefore, the laser plasma breakdown temperature based on inverse bremsstrahlung absorption is determined.