Basic Studies for the Mechanism of Gas Discharge Caused by Laser and its Applications to the Laser-Induced Lightning

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In this project we studied the basic process and experimental study of laser-induced discharge under long gap condition to put the laser-induced lightnin for practical use in the near future. Summary of these researches are as follows :(1)To put the laser-induced lightning for practical use, the laser-induced plasma length must be 20m at the shortest because it has to break through the space charge layr which is produced by ground corona discharge.(2)Laser-induced disharge level was lowered significantly compared to normal gas discharge under the following conditions : applied voltage is DC, gap length is 20-30mm, plasma channel is produced near the electrode which is relatively positive, positive electrode configulation is flat and there is no positive side corona. On the other hand, in the case of long gap and lightning impulse, these performances are reversed.(3)Laser induced discharge is mainly produced inside the rarefied ar. It is caused by gas expansion for heating up.(4)Accordi … More ng to the observation of the plasma which is produced by KrF excimer laser or YAG laser, shock wave is generated immadiatly after plasma production within 1mus and is spread by sonic speed. After plasma channel is produced there are some spots where plasma density is rarefied. The electron densities are in the range of 10^<23>-10^<24>m^<-3>.(5)According to the observation of the plasma which is produced by CO_2 laser, the electron density was about 10^<24>m^<-3>.(6)The influence of rain or fog is not so significant in the experiment of the induced discharge by CO_2 laser under the condition of 3m gap length.(7)We observed in almost all experiments the time-lag(10-100mus) between laser irradiation and 50% spark over.We succeeded laser induced discharge between the electrodes of 8m gap length, using the outdoor impulse genarator and two sets of CO_2 laser(rated out put energy are both 45J).(9)According to the experiment mentioned No.(8) item, the effective plasma length induced by two sets of CO_2 laser is 1.5m, breakdown voltage is 3.8MV which is 1MV lower value compared to the normal breakdown voltage. Less