Dynamics of spatially and temporally decaying arcs for lightning discharge initiation

Summary form only given. In the field of laser initiated lightning discharge research for electric power network protection, some drastic breakthroughs are necessary to apply this technique commercially, other than the conventional approach only for chasing after the higher laser power. One of the keys seems to be in the experimental results found in the same field. The laser produced plasma in quasi steady high electric field is known to show a strange feature. It has the peak lightning-triggering efficiency at around 100 /spl mu/s after a sub-micro second laser irradiation. From the existing computer simulation, this time scale should be far longer than the recombination and attachment time scale for free electrons in air. In this sense, the dominant constituents for lightening initiation are not free electrons but excited gases in certain conditions. We had set up an experiment with a transversally accelerated arc. This uses a modified version of a rail-gun type system but in high pressure air. This produces a rapidly moving high current arc armature with 10 kA peak and 10 ms current decay time. This time scale is slow enough to be considered as a quasi-DC condition for this application. The time scale of experimentally obtained hot gas decay is about 100 us and the laser pulse duration is in the order of 10 ns. The paper focuses on the mechanism and efficiency of charged particle removal from this plasma with experimental evidence. These results are summarised with the detailed comparison with the simulation and unresolved questions shown.