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Re: Streamer colour

Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:

Original poster: Ed Phillips <evp@xxxxxxxxxxx>
I have a comment.  In running my VDG and observing sparks in a dark
room I see an interesting effect.  Often I get a segmented spark which
looks about like this:
First part, coming from the top terminal, is a fairly straight 4" spark,
ending in
Second part, a point from which am "umbrella" of purplish sparks emerge
and strike whatever.
I don't know what causes this phenomenon (bet Antonio does), but it is
obvious that the current density for the bright blue part must be higher
than that of the whole bunch of purple coming front of it.

This is "positive corona". A brush of thin filaments that join in a thick straight segment at the base. Possibly generated in the same way as lightning, with bunches of negative ions converging to a point where the discharge is suddenly completed by a "positive streamer", the straight segment. If you look carefully at a DC spark, you see the straight segment at the positive end. And if you look in the dark, weakening the spark by adding some series resistance, it's possible to see that the brush of thin filaments is always present, with the spark channel forming through one of them. I still have to find a way to photograph this.

Positive at the right side. Note the straight segments:

Antonio Carlos M. de Queiroz