From: Mike Rosing <rosing@neurophys.wisc.edu>
Newsgroups: sci.physics.plasma
Subject: Re: REQ: Arc discharge build-up time?
Organization: Medical Electronics Lab.
References: <ad2d5k$8i1a$1@saturn.cs.uml.edu>


Dudelman wrote:
> I was wondering if there's any information out there about the time
> that an arc discharge requires to build up?

What do you mean by "build up"? The time before an ionization streamer
appears, or the time it takes for the streamer to form?

> Qualitatively I assume that this time is dependent on
>
> - voltage (the higher the quicker),

yes

> - air density (the thinner the faster),

For atmospheric yes, but once you get down to millitorr things change.

> - air humidity (humid air is easier to polarize hence
> the more humidity the faster the arc build-up),

No, water is harder to ionize that O2 or N2 so more humidity makes
things
harder to arc. Water also helps quench the arc faster.

> - electrode/terminal geometry (the sharper the quicker?)

usually, but surface roughness can improve arcing (lots of tiny sharp
points
work better than one large sharp point).

> Are there any quantitative theories/measurements/experiences
> available? I'd appreciate any comment.

Yes, look up Townsend. He photographed lightning type arcs and measured
the time and length of typical arcs to go from one plate to another in
air.
I think it was in the early 1900's, but some of it could have been in
the 1930's.

Patience, persistence, truth,
Dr. mike