低压氩气电感耦合等离子体特性分析及光谱诊断

电感耦合等离子体具有电子密度高、放电面积大、工作气压宽、结构简单等特点，在等离子体隐身领域具有突出的潜在优势。相对于开放式等离子体，闭式等离子体更适应于飞行器表面空气流速高、气压变化大的特殊环境。研究着眼于飞行器关键部件的局部隐身应用，设计了一种镶嵌于不锈钢壁中的圆柱形石英腔体结构，利用电感耦合放电的方式在腔体中产生均匀的平板状等离子体。由于增加了接地金属，降低了腔体内的钳制电位，同之前的纯石英腔体相比，该结构显著改善了等离子体的均匀性。研究了该闭式腔体内氩气电感耦合等离子体（ICP）的放电特性和发射光谱，实验中放电功率达到150 W时，可以明显观察到ICP的E-H模式转换，此时发射光谱和电子密度都呈现阶跃式增长。氩气发射光谱强度随放电功率升高显著增加，但是不同谱线强度增加幅度并不一致，分析认为是受不同的跃迁概率和激发能的影响。根据等离子体的发射光谱，利用玻尔兹曼斜率法对电子激发温度进行诊断，得到电子激发温度在2 000 K以上，并且随功率升高而降低，因为功率增大使电子热运动增强，粒子间的碰撞加剧，碰撞导致的能量消耗也更大。电子激发温度沿腔体径向呈近似均匀分布，分布趋势受功率影响不大。针对利用发射光谱诊断电子密度误差较大、计算繁琐的问题，引入Voigt卷积函数，经过拟合滤除多余展宽项的影响，得到准确的Stark展宽半高宽。最终利用发射光谱Stark展宽法计算了电子密度，腔体中心处的峰值密度可以达到7.5×1017 m-3。随着放电功率增大，线圈中容性分量降低，耦合效率增大，电子密度随之增大，但空间分布趋势基本不受功率影响。

Characteristics Study and Parameters Diagnosis by Spectral Analysis of Low Pressure Argon Inductively Coupled Plasma

The inductively coupled plasma (ICP) has more advantages over other plasma sources in radar stealth, including simple antenna structure, a wide pressure range, large area and high electron density. Compared with the open-type plasma, closed-type plasma is more compatible with the flying environment of aircraft, where the air flows fast and pressure changes fiercely. A newly designed cylindrical closed chamber made of quartz windows inlaid in stainless steel was used to generate planar ICP for the potential application in stealth design of aircraft local. Compared with previous all-quartz chamber, the new structure effectively improved the homogeneity of ICP because of the ground connection. The discharging characteristics and emission spectrum of ICP in the closed chamber was studied. Obvious E-H mode transition was observed when the power came to 150 W in experiment. The spectrum intensity and electron density increased in a huge step at the transition point. Over the whole discharging progress, the spectrum intensity increased with power, but because of the diversity in transition probability and excitation energy of spectral lines, the increasing amplitude was also different. Based on the emission spectrum of ICP, the electron excitation temperature was diagnosed by the Boltzmann slope method. The electron excitation temperature was above 2 000 K and the higher of the power, the lower of the temperature. Because higher power enhanced the thermal motion of electrons and then the collision between particles became fiercer. This kind of collision consumed more energy so the temperature came down. The distribution of electron excitation temperature along the radial direction was approximately homogeneous. And the power had little influence on the distribution. A Voigt convolution function was introduced to solve the problem of big error and cockamamie calculation about spectrum diagnosis of electron density. The interferential broadenings of argon emission spectrum were eliminated by fitting calculation. So the accurate full width at half maximum of Stark broadening was obtained. Then the electron density was calculated by Stark broadening method. The peak electron density came to 7.5×1017 m-3 at the center of chamber. The electron density increased with power because the coupling efficient was enhanced. Power had little influence on the spatial distribution of electron density.