| Popis: |
In this study we use an experimental investigation to shed light on the lightning inception problem. From atmospheric observations, it is known that the electric fields in thunderclouds are significantly lower than required for electric breakdown in air. One theory to explain lightning inception is that hydrometeors, i.e. any liquid or solid water particles formed in the atmosphere, greatly enhance the local electric field and can thereby initiate an electron avalanche leading to a streamer discharge. In this study, we investigate streamer initiation in the presence of artificial particles with different shapes. A metal or dielectric (TiO2) particle is suspended between a high-voltage and a grounded planar electrode which are separated by 16 cm in 50 mbar air. The particles are shaped as ellipsoids with a length of 8, 4, 2, and 1 cm and with different aspect ratios. A negative high voltage pulse is applied with a rise time of 30 ns, a pulse width of 1–10 μs, a repetition rate of 1 Hz, and a maximum voltage between 1 and 50 kV. Results show that the required background electric field for breakdown in the presence of a dielectric particle is decreased to 0.4 times the air breakdown field. Moreover, we observed bipolar streamer development from the particles where negative streamers are thicker and slightly slower than positive streamers. Finally, we found that streamers from longer particles are thicker and faster. |
