等离子体的三频点微波透射衰减诊断方法

 依据微波在等离子体中的传播特性，并利用微波透射非磁化等离子体时在三个相邻频率点的透射能量衰减值，可同时诊断等离子体中的电子密度和电子碰撞频率。使用该方法对100～700 Pa范围内氦气辉光放电等离子体进行了诊断，选择6.2，6.8和7.4 GHz三个频率点，并与使用双探针诊断的诊断结果进行比较。结果表明：两种诊断方法所得碰撞频率基本一致；微波透射衰减法诊断出的电子密度值与探针法的诊断结果在同一数量级(1016 m^-3)，但前者约是后者的1.67倍。最后对造成这一差异的原因进行了分析。三频点微波透射衰减诊断方法可用于较高气压及其它静电探针使用受限的环境下，并且可以采用能量较小的微波，不会对等离子体本身造成显著影响，适用于等离子体的初步诊断。

Plasma diagnostic method using the transmission attenuation of microwaves at three frequencies

The plasma frequency and the electron collision frequency can be deduced with the plasma diagnostic method which utilizes the transmission attenuation of microwaves at three frequencies in a non-magnetized plasma.Then the electron density can be obtained from the plasma frequency. The measurement system consists of a sweep oscillator,a pair of broad-band horns,and a scalar network,etc.The plasma produced by an electric discharge of helium with the pressure range 100~700 Pa in a closed cavity is diagnosed by this way at three frequencies of 6.2,6.8 and 7.4 GHz.As a comparison,the Langmuir double probe method is used at the same time.The results indicate that the electron collision frequencies got by these two methods are coincident.The electron densities got by the attenuation of microwave are universally larger than those got by the double probe diagnostic method,but they are at the same magnitude(1016 m-3).The transmission microwave attenuation method is suitable for the elementary diagnosis of the plasma at low and high pressure.