The mechanism of the guidance effect of laser plasmas on electrical discharges has been studied. A 45 J CO2 laser pulse produces many spherical plasmas over a gap of up to 2 m, and the laser-guided discharge is formed along the plasma by the application of a lightning impulse voltage. Unusual properties of the laser guided discharge are obtained from streak photographs of the discharge development. The laser produced plasmas guide streamers and leaders from a negative electrode more effectively than from a positive electrode. The discharge development from the negative electrode plays an important role in the guidance effect.
Experiments to guide electric discharges with a chain of apparently discrete a i r -breakdown plasmas ( p l a s m a channel) produced by a l a s e r were c a r r i e d o u t . The electric d i s c h a r g e was guided u p t o 2m with a high power CO2 laser focused by a 10 -m focal l e n g t h m i r r o r . V o l t a g e w a s a p p l i e d a t s e l e c t e d delay times 5 f o l l o w i n g l a s e r r a d i a t i o n . The r el a t i o n s b e t w e e n 50% f l a s h o v e r v o l t a g e of a g a p filled with laser -produced plasmas and delay times r , between the guided length and the peak of the appiled voltage, were obtained experimentally. The e f f e c t s of t h e p o l a r i t y of a n a p p l i e d v o l t a g e a n d t h e p o s i t i o n of t h e p l a s m a c h a n n e l o n f l a s h o v e r voltage a r e described. Development characteristics of the guided discharge were a l s o investigated.
Bead-like plasmas produced by a laser have guided and triggered electrical discharges in air gaps. The physical parameters (electron density, electron temperature, geometric structure) of the laser-produced plasmas have been measured using spectroscopy and laser interferometry. We compared the results of these measurements with the characteristics of laser-guided discharges, and found that the mechanisms of the guiding ability of the laser can be explained by the behaviour of the plasma as a conductor (metal ball model). We conducted model experiments of the laser-guided discharges using small metallic balls. The features of the discharge guided by metal balls were similar to those guided by laser-produced plasmas. We thus concluded that the behaviour of the plasma plays an important role in triggering and guiding the discharges.
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