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

本项目主要研究长间隙条件下激光诱导放电的基本过程和实验研究，为激光诱导闪电的实用化奠定基础。（1）要使激光诱导闪电实用化，激光诱导等离子体必须穿过地面电晕放电产生的空间电荷层，其长度最短为20 m。（2）在外加电压为直流、间隙长度为20- 30 mm、等离子体通道位于相对正的电极附近、正电极表面平整且无正侧电晕的条件下，激光放电水平较普通气体放电显著降低。而在长间隙和雷电冲击的情况下，这些性能则相反。（3）激光诱导放电主要发生在稀薄的Ar内部。它是由气体膨胀加热引起的。（4）协议 ...更多信息 对KrF准分子激光器或YAG激光器产生的等离子体进行了观测，发现在等离子体产生后1 μ s内即产生冲击波，冲击波以声速传播。等离子体通道形成后，存在等离子体密度稀薄的区域。电子密度在10^<23>-10 ^<24>m2之间<-3>。（5）对CO_2激光器产生的等离子体进行了观测，电子密度约为10 μ <24>m ~ 2<-3>。（6）在3 m气隙条件下，雨雾对CO_2激光诱导放电的影响不大。(7)We在几乎所有的实验中都观察到激光照射到50%火花放电之间的时间滞后（10- 100 μ s），我们用户外脉冲发生器和两台CO_2激光器（额定输出能量均为45 J）成功地在8 m间隙的电极间进行了激光诱导放电。（9）根据上述实验，(8)第一项，两组CO_2激光器产生的等离子体有效长度为1.5m，击穿电压为3.8MV，比正常击穿电压低1 MV。少

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