大气压低温氦等离子体射流的诊断研究

为了加快低温氦气等离子体射流的工程化进程，通过自主设计的同轴式介质阻挡放电等离子体射流发生器，在放电频率10 kHz，一个大气压条件下产生了稳定的氦气等离子体射流。通过分析不同工况下的电压电流波形可以发现单纯增加氦气体积流量只能小幅的增加电流脉冲幅值，而对放电时间、电流脉冲数的影响不大。增加放电峰值电压时电流脉冲幅值会得到较大幅度增加。通过发射光谱法对大气压氦气等离子射流的活性粒子种类、电子激发温度、电子密度进行了诊断。结果表明，大气压氦气等离子体射流中的主要活性粒子为He Ⅰ原子、N₂第二正带系、N+₂的第一负带系、羟基（OH），H原子的巴尔末线系（H_α和H_β）与O原子，这表明虽然该试验中使用的氦气纯度已达99.99%，但其中仍残留有少量的空气，同时放电时大气中的空气会被卷吸到放电空间发生电离。还可以发现，主要活性粒子的相对光谱强度随氦气体积流量的增加及放电峰值电压的增大均呈现上涨的趋势。选用He Ⅰ原子的四条谱线对不同试验工况下的电子激发温度进行了计算，得到大气压氦气等离子体射流的电子激发温度在3 500~6 300 K之间，电子激发温度随放电峰值电压与氦气体积流量的增大总体上呈现上升的趋势。但由于反向电场的存在，某些峰值电压可能会出现电子激发温度下降的情况；根据Stark展宽原理对大气压氦气等离子体射流的电子密度进行了计算，发现电子密度的数量级可达1015 cm-3，同时增大峰值电压与氦气体积流量均可有效的提高射流中的电子密度。这些参数的研究对氦气等离子体射流在工程实际中的应用具有重要意义。

Diagnosis of Atmospheric Pressure Helium Cryogenic Plasma Jet

In order to accelerate the process of helium plasma jet’s engineering，a stable helium plasma jet was produced in the atmosphere through a self-designed coaxial Dielectric Barrier Discharge structure with a discharge frequency of 10 kHz. By analyzing the voltage and current waveform under different working conditions, it can be found that simply increasing the volume flow of helium gas can only increase the current pulse slightly, but has little effect on the discharge time and the number of current pulses. However, when the peak discharge voltage is increased, the current pulse amplitude increases significantly. The types of active particles, electron excitation temperature and electron density of atmospheric pressure helium plasma jet were diagnosed by emission spectroscopy. The results show that the main active particles of helium plasma jet are He I atom, N₂ second positive band system, N+₂ first negative band system, hydroxyl (OH), H atom Balmer line system (H_α, H_β) and O atom. It shows that although the purity of the helium gas used in this test has reached 99.99%, there is still a small amount of air remaining. At the same time, the air in the atmosphere will be sucked into the discharge space and be ionized. It can be found that the relative spectral intensity of the main active particles showed an upward trend with the increase of the volume flow of helium gas and the increase of the peak discharge voltage. The electronic excitation temperature under different test conditions was calculated by the Boltzmann slope method between 3 500 to 6 300 K. With the increase of the discharge peak voltage and helium gas’s volume flow rate, the electron excitation temperature basically shows a rising trend. However, due to the presence of a reverse electric field, the electronic excitation temperature may show a downward trend at some certain peak voltages; According to the Stark broadening principle, the electron density of the atmospheric pressure helium plasma jet was calculated, and it is found that the electron density can reach the order of 1015 cm-3 while increasing the peak voltage and helium volume flow can effectively increase the electron density in the plasma jet. The study of these parameters is of great significance for the application of helium plasma jets.