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

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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.