Formation of a negative impulse discharge induced by an XeCl excimer laser in a long rod-to-rod electrode gap in air.

Negative discharge induction experiments were performed with a rod-to-rod electrode configuration having a gap length of 0.8 m using a high-power XeCl excimer laser of maximum output energy of 2 J/pulse and an impulse generator of maximum voltage of 1.2 MV. Development of a leader in the laser-ionized plasma channel was observed by using an image converter camera. When a XeCl excimer laser is applied at a carefully controlled instant, the guiding effect for an impulse discharge is optimized. Three main results were obtained. First, the discharge started near the focal point and then developed bidirectionally toward the high-voltage electrode and the grounded electrode. Midgap leaders were frequently observed. Second, it was observed that the lifetime of the laser-ionized plasma channel was about 1 Ps. Third, the discharge processes were classified into six stages. The mechanism of the streamer and leader propagation is discussed. [ABSTRACT FROM AUTHOR]