CHARACTERISTICS OF TIME-EVOLUTION OF LASER-PRODUCED PLASMA IN WATER VAPOR

作为激光感生闪电的先进方案--闪电消光的基础研究，我们对激光等离子体在水蒸气中的时间演化特性进行了两年的实验研究。本文从两个方面进行了实验研究，取得了以下成果。用分解成波长分量的方法测量了等离子体辐射的时间演化，并对得到的各光谱进行了分析。点火后对连续谱进行了分析，得到了5000-7000K的电子温度；经过较长时间(10musec以上)对线谱进行了分析，得到了10^&lt；22&gt；-10^&lt；23&gt；m^&lt；-3&gt；衰变时间常数为8musec。存在的问题是由连续谱分析得到的电子密度值的可靠性和长时间内未知的电子温度。我们通过施加一个弱电场来研究等离子体的特性。从等离子体中汲取的电荷量与电场强度成正比，与电极之间的距离成反比。为了考察其随时间的变化，采用了脉冲电场的方法。结果表明，等离子体和/或水蒸气产生的激波影响带电粒子的运动。一个精确的模型对于解释结果和了解等离子体特性是必要的，但目前的模型只解释了部分结果，不足以完全解释。我们还需要更多的实验数据。虽然还存在一些问题，但我们已经获得了闪电熄灭这一远景目标的初步数据。

As a fundamental research of extinction of lightning, which is the advanced scheme of laser-induced lightning, we have experimentally investigated the characteristics of time-evolution of laser-produced plasma in water vapor for two years. The experiments have been carried out from two kinds of aspects, and we have obtained following results.1. The time-evolution of the radiation of the plasma is measured with resolving into its wavelength components, and obtained each spectrum is analyzed. Just after the ignition, the continuous spectra are analyzed, and we have obtained the electron temperature of 5000-7000K.After a long period of time (over 10musec) , line spectra are enalyzed, and we have found the electron density of 10^<22>-10^<23>m^<-3> and decay time constant of 8musec. The remained problems are the reliability of the value of electron density by the analysis of continuous spectra and the unknown electron temperature in a long period of time.2. We have examined the characteristics of plasma by applying a weak electric field. The amount of electric charge drawing from the plasma is proportional to the electric field strength and inversely proportional to the distance between electrodes. In order to examine the time variation, the pulsed electric field is applied. The results suggest that the shock wave produced with the plasma and/or water vapor affect the motion of the charged particles. A precise model is necessary to interpret the results and to know the plasma characteristics, but the present model just explains partial results, and it is insufficient for complete explanation. More experimental data are needed.Some problems are remained, but we have obtained the initial data for the farseeing aim of the extinction of lightning.