Experiments of discharge guiding using strongly and weakly ionized plasma channels for laser-triggered lightning

Abstract

Generation of a long laser-plasma channel capable of triggering and guiding an electrical discharge is a crucial issue for laser-triggering protection system. We make a long plasma channel to increase the probability of triggered lightning by laser. To produce a long laser plasma channel, we proposed a new technique called hybrid plasma channel method which combines weakly (<1O' cm3) and strongly (>>lO' cm3) ionized plasma channels to maximize laser-energy efficiency of discharge guiding. We investigate the characteristics of the hybrid plasma channel method through several laboratory experiments.The weakly ionized channel was generated by ultra violet laser pulses (248nm) in air. As the number density of electrons in weakly ionized channel is proportional to 1 .1 power of laser intensity (5.5 eV), nitrogen and oxygen molecules can not attributed to the source of ionized plasma. It is suggested that dissociation process of impurities in air whose density is 10' '-1012 cm3 plays an important role in plasma formation and leader triggering effect.The 50 % flashover voltage (V50) using the hybrid plasma channel method is lower than that without the weakly ionized plasma channel. It was also found that higher repetition rate of the plasma generation on lowers the V50 furthermore.

Triggering and guiding HV discharge in air by filamentation of single and dual fs pulses

“…The basic researches on the laser lightning control are mainly carried out in laboratories using artificial HV, because of the randomness and danger of the natural lightning. Since 1980s, Japanese scientists have done many works on laser-triggered HV discharge using high power CO 2 laser [2,3]. The CO 2 laser produces a discontinuous plasma channel composed by serials of separated breakdown sparks, and large amount of laser energy was needed to trigger a long gap discharge.…”

Long Gap Discharge Guiding Experiments Using Strongly and Weakly Ionized Plasma Channels for Laser Triggered Lightning

“…Electron densities produced by KrF-laser are also shown in Fig. 3 [6,7] by square. The data of the electron density produced by UV-and KrF-laser were allocated on a same line.…”

“…3 [5] by circle. From this result, the plasma density of 10 13 cm −3 was generated with a laser intensity of 2× 10 9 W/cm 2 .…”