Re: Gap Question

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Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 


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Sent: Monday, February 23, 2004 7:50 PM
Subject: Re: Gap Question


 > Original poster: "June Heidlebaugh" <rheidlebaugh-at-desertgate-dot-com>
 >
 > You have made an incorrect assumption. If you look at a gap that is firing
 > or photograph you will find the arc is spread over a distance of the gap
in
 > parallel electrodes. Dr Res has some fine photographs.
 >     Robert   H

Somehow, I don't think this is the case for a single discharge. A photo may
show an apparent "wide spark", but there's fairly good theory and
experimental evidence that you form a single "cathode spot" (up to a few
tens or hundreds of amps) of roughly constant size.  If the current gets
really high, you can form multiple "cathode spots".  If the spark/arc is of
long duration (time wise), the spot moves around.  There was a great survey
paper in IEEE Proceedings back in the 1970s that covered all this in quite a
bit of detail.  The cover of the issue had a (stylized) photograph of the
track of the cathode spot for a high power vacuum arc.

There was another paper (in that issue, I think, but I'm not sure) about
using high power arcs for transmitting power across a gap. It was intended
as a replacement for mechanical sliding brushes as  in supplying power to a
high speed electrically powered train.