Fundamental Study due to Quantitative Measurement of Light Emission from Induced Discharge in Cloud

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The purpose of this project is to clarify various characteristics of laser produced plasma to trigger lightning in cloud. The results are as follows.The experiment is performed by using water vapor as a target for the plasma production. The threshold laser energy for plasma production is reduced by 1/3 in this conditon. Using the optical image processing system for discharge light measurements, which consists of an image converter camera and a CCD camera, the spatial distributions of light emission from laser produced plasma and their temporal developments are successfully measured. The analyzing programs for these experimental data are newly coded on the usual personal computers and the engineering work station. The expansion and decay phases are quantitatively evaluated by the result of analysis. On one hand, the numerical analysis, in which the shock wave induced by a point explosion is treated, is performed to clarify the physical mechanism. The calculated results are well agree with the experimental results. The behavior of the plasma in the phase after the laser energy deposition can be described by the characteristics of shock wave propagation.The experiment is developed to spectrum analysis of the light emission. The absolute intensity of light is measured in two dimensional space of time and wavelength. The calibration experiments of the measurement system are carried out to short-gap discharge in air SF_6, which show the effectiveness of the system. The measurement is applied to the laser produced plasma, and its density and temperature are estimated. The estimated values are similar with a report by other groups.The further experiments, the measurement of induced current in the weak electric field, are already started. The more detailed and reliable knowledge will be obtained by the synthetic analysis with the result of this project.