Re: Streamer colour

["Tesla list" <tesla@xxxxxxxxxx>]

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:
http://www.coe.ufrj.br/~acmq/trmspk.jpg
http://www.coe.ufrj.br/~acmq/bbspark.jpg

Antonio Carlos M. de Queiroz