基于连续谱的氩气纳秒脉冲放电中电子温度的研究

采用了一种针对针的放电结构，将其放置在一个高纯氩气的密闭腔室中，通过施加正极性的过电压产生可重复的大气压纳秒脉冲放电，并提出建立大气压放电的连续辐射模型来诊断氩气纳秒脉冲放电中的电子温度。实验利用电压和电流探头分别获取放电过程中的电压和电流波形图，其放电脉宽约为20 ns。通过消色差透镜、单色仪和ICCD等光学系统的组合来测量放电正柱区在不同时刻（0<t<20 ns）的时间分辨发射光谱。结果表明，放电中连续谱的强度随时间先增加（0<t<10 ns）后减小（10 ns<t<20 ns），但是氩原子的谱线强度则随时间的增加而一直增大。研究表明连续谱强度与电子密度成正相关，因而电子密度随着时间也是先增加而后减小，这与放电电流的变化规律是完全一致的。根据连续谱模型拟合得到放电过程中（0<t<10 ns）的电子温度为(1.4±0.2) eV。随着驱动电压的下降（10 ns<t<20 ns），电子温度逐步减小至0.9 eV。在0<t<10 ns中，激发态氩原子主要是由电子碰撞激发产生的，因而谱线强度随着电子密度的增加而增大。然后，随着电子温度的减小，Ar+₂复合反应速率激增，导致电子与离子的复合过程主导产生激发态氩原子，即谱线强度继续增大。通过加入0.5%的水蒸气以获取OH的振转光谱。实验发现，OH(A)的产生机制使其偏离玻尔兹曼平衡分布，本文采用了双温的OH(A-X)光谱模型来考察气体温度。在放电过程中，气体温度保持不变，大约为400 K。此外，水蒸气的加入使得短波长的连续谱发生显著增强。光谱分析认为H₂O在放电中能够解离产生H₂，继而与氩原子的亚稳态发生能量转移生成激发态H₂(a3Σ+_g)。H₂(a3Σ+_g)将会自发辐射跃迁到排除态H₂(b3Σ+_u)，同时发射短波长的连续谱。由于短波长的连续谱对电子温度（T_e>1 eV）的响应较为灵敏，所以载气中少量的水蒸气将会对连续谱诊断电子温度带来较大的影响。

Research on the Electron Temperature in Nanosecond Pulsed Argon Discharges Based on the Continuum Emission

In this paper, atmospheric pressure nanosecond pulsed discharges in pin-to-pin geometry are very easily reproducible by applying a positive overvoltage, and such discharge system is placed in a sealed chamber filled with high purity argon gas. A continuum radiation model for the atmospheric pressure discharges is proposed to diagnose the electron temperature of the nanosecond pulsed argon discharges. The high voltage and current probes monitor the voltage and current waveforms during the discharge, and the discharge pulse width is about 20 ns. The time-resolved emission spectra of the discharge column at different times (0<t<20 ns) are measured by the combination of optical systems, such as achromatic lens, monochromator and ICCD. The results indicate that the continuum emission intensity of the discharge increases with time during the period of 0<t<10 ns, and then decreases during 10 ns<t<20 ns. However, the intensity of argon lines always increases with time. As the intensity of continuum emission is positively correlated to the electron density, the electron density also increases firstly and then decreases, which has the same tendency as the discharge current. According to the continuum radiation model, the electron temperature during the discharge (0<t<10 ns) is measured to be (1.4±0.2) eV. As the driven voltage drops (10 ns<t<20 ns), the electron temperature decreases gradually to 0.9 eV. Our research suggests that the excited argon atoms are mainly populated by electron impact excitation during 0<t<10 ns, and thus their emission intensities increase with the electron density. Afterwards, due to the decreasing of electron temperature, the rate of Ar+₂ ions recombination reaction increases dramatically. The production of excited atoms is governed by the electronion recombination processes, leading to increase their emission intensities further. The virotational spectrum of OH species is detected by adding 0.5% water vapor into the working gas. It is found that the production mechanisms of OH(A) make it deviated from Boltzmann distribution. In this work, a two-rotational temperatures OH(A-X) spectral model is employed to examine the gas temperature. During the discharge pulse, the gas temperature remains invariant around the value of 400 K. Moreover, the addition of water vapor causes the increase of the intensity of the continuum in the short wavelength range. It is analyzed that H₂ could be produced by the dissociation of H₂O in the discharge and then excited to the excited state H₂(a3Σ+_g) by means of the energy transfer reaction from argon atoms in a metastable state. Finally, H₂(a3Σ+_g) decays by spontaneous radiation to the repulsion state H₂(b3Σ+_u) and emits the short-wavelength continuum emission. The electron temperature (T_e>1 eV) is very sensitive to the short wavelength response of the continuum spectrum. So even if the working gas contains a small amount of water vapor, it will greatly influence the electron temperature diagnosed by the continuum radiation.