等离子体状态参数测量是研究等离子体特性, 开展等离子体模拟再入环境、 等离子体隐身、 等离子体减阻以及边界层控制等研究的重要基础。 利用等离子体射流的自发辐射光谱, 提出了一种基于光学多普勒频移效应的等离子体超声速射流测速的方法。 首先, 测量了等离子体中Ar原子产生的自发辐射光谱, 选择696.54 nm的特征谱线, 作为等离子体发生器测速实验的运动光源; 其次, 使用光谱仪、 传能光纤、 EMCCD相机和高光谱分辨法布里-珀罗(F-P)干涉仪, 设计了高温等离子体速度测量光路; 最后, 在氩壁稳电弧等离子体发生器上, 开展了超声速射流速度测量实验。 实验中, 同一测点的Ar原子产生的自发辐射光谱, 分别被与等离子体射流运动方向成49°和90°夹角的收集透镜收集进入光谱仪, 经光谱仪分光后仅保留特征谱线696.54 nm附近自发辐射光进入传能光纤, 从而消除其他波长的自发辐射光的影响; 光谱仪输出的特征辐射光谱, 经光纤传输及透镜整形成平行光后, 精细度30、 自由光谱范围6.6 GHz的F-P干涉仪, 形成多光束干涉圆环, 并由EMCCD相机采集, 实现对特征谱线的超高精度分辨; 根据多普勒原理, 不同角度收集的同一测点处Ar 696.54 nm特征谱线的频移将有所不同, EMCCD采集的干涉圆环半径也将不同, 通过测量同一级次不同收集方向特征谱线形成的干涉圆环半径改变量, 可测得高温等离子体射流流动速度。 针对同一喷管开展了两车对比试验, 实验测得两车射流轴向速度分别为791和783 m·s^-1, 具有较好的重复性。 结果表明基于多普勒效应, 利用高温气体自发辐射光谱, 结合高光谱分辨F-P干涉仪, 能够实现高温等离子体射流速度的精确测量, 该方法属于非接触测量, 不干扰流场, 尤其适用于传统传感器难以应用的高温流场测量。

The measurement of plasma state parameters is an important basis for studying plasma characteristics, including plasma simulated reentry environment, plasma stealth, plasma drag reduction, and boundary layer control. Based on the spontaneous emission spectrum of the plasma jet, a new method of plasma supersonic jet velocity is proposed in this paper. Firstly, the spontaneous emission spectrum generated by argon atoms in the plasma was measured, and the characteristic spectral line of 696.54 nm was selected as the moving light source for the speed measurement experiment of the plasma generator; secondly, the optical path of speed measurement was designed by using a spectrometer, energy transmission fiber, Electron-Multiplying CCD (EMCCD) camera and high spectral resolution Fabry-Perot (F-P) interferometer for high temperature plasma; finally, the velocity measurement experiment was carried out of supersonic jet on an argon wall stabilized arc plasma generator. In this experiment, the spontaneous emission spectrum of argon atom at the same measuring point was collected into a spectrometer by the collecting lens, which wasan angle of 49°and 90°between with the plasma jet motion direction, respectively. After being split by the spectrometer, only the characteristic line of 696.54 nm was retained into the energy transmitting optical fiber, to eliminate the influence of the spontaneous emission spectrum of other wavelengths; the characteristic emission spectrum from the spectrometer, which was transmitted by optical fiber and shaped into parallel light by the lens, irradiated the F-P interferometer with a fineness of 30 and a free spectral range of 6.6 GHz, then a multi-beam interference ring was formed and collected by an EMCCD camera, so as to realize the ultra-high precision resolution of characteristic spectral lines. According to the Doppler principle, the frequency shift of Ar 696.54 nm at the same measurement point collected at different angles was different, and the radius of the interference ring collected by EMCCD was also different. By measuring the radius of the interference ring formed by the characteristic spectral lines for the same level and different collection directions, the flow velocity of the high temperature plasma jet can be computed. The comparative experiments of two vehicles were carried out for the same nozzle, and the axial velocities of the two vehicles were 791 and 783 m·s^-1, respectively, which had good repeatability. Based on the Doppler principle, the results show that, using the spontaneous emission spectrum of high temperature gas, combined with the high spectral resolution F-P interferometer, the high temperature plasma jet velocity can be accurately measured. This method belongs to non-contact measurement and does not interfere with the flow field and is especially suitable for the measurement of high temperature flow field, which is difficult to be applied by traditional sensors.