Abstract：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.
