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Re: 20 joules at 100 bps vs 4 joules at 500 bps



Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 11:04 PM 8/4/2005, you wrote:
Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:

Original poster: "Denicolai, Marco" <Marco.Denicolai@xxxxxxxxxxx>
Hello Jim, all,
Based on my readings there are 3 different situations for breakdown:
- small gaps (some cm), Efield required 30 kV/cm, breakdown with avalanche (Townsend).
- medium gaps (< 1 m), Efield required 5 kV/m, breakdown with stable streamers and final jump.
- large gaps (> 1 m), Efield required only 1 kV/m, breakdown with leader-streamer phases and final jump.
These phenomena are very well documented, although usually with different names and in not such a clear manner. So, for a 2 m breakdown you need a 30 kV/m on the toroid surface, then at least some 5 kV/m within 1 m from it and the rest of the travel will succeed if 1 kV/m can be ensured.

This is interesting. In looking at sparks between two balls, there is evidently a distance where sparks cease to occur, even with corona at the spheres still occurring. A certain minimum required electric field in the space between the terminals is evidently required. But values as 5 kV/m seem too low, at least for relatively short sparks. For example, I have an electrostatic machine that can produce sparks with up to 16.5 cm between 2.4 cm spheres. I can simulate this in the Inca program, that predicts a breakdown voltage of 66.5 kV. Charging the balls to +/- 33.25 kV, the electric field exactly between the balls has a minimum of 96 kV/m. So, for sparks in this range, apparently something as 100 kV/m is required. But this is of a single spark. RF sparks, that grow progressively, may need less.


Maybe it's more "long sparks" rather than RF sparks. Lightning isn't RF and it grows progressively.

You need some field to keep the ionized particles moving in "some direction", or else after ionization (by whatever means) they'll just tend to drift out in all directions. If you see photos of laser induced breakdown (like the famous 20kW gasdynamic CO2 laser picture in the 1970s) you see blobs of ionized air along the beam path, but no tendency for them to elongate, etc.