Re: vacuum spark gap

Gavin is basically right.  A vacuum is a fairly good insulator.  The
breakdown is by field emission of electrons, which knocks a few electrons
off the electrode, which then starts to get warm, and then, once it's
going, vaporized metal ions keep it going.  It doesn't take much metal to
do this BTW.

Xrays would be a problem when you get over about 10 kV, but assuming you
put the thing in a metal can, it shouldn't be a big problem. 

Quenching may prove to be a problem.

There are several on this list (and in the archives) who have made gaps
from retrofitted vacuum circuit breakers.  A little practical experience is
worth hours of dialectic.

> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: vacuum spark gap
> Date: Saturday, April 29, 2000 11:01 PM
> Original Poster: "Gavin Dingley" <gavin.dingley-at-astra.ukf-dot-net> 
> Hi Al,
> correct me if I'm wrong, but don't you require a gas present to ionize
> form a
> conducting channel. If you have a vacuum, then there are no gases
> so how
> does it conduct? The only other way as far as I can see it, is for the
> particles from the electrodes forming the conducting channel. If this is
> the case,
> then a real high voltage is required before it will brake down. In this
> case there
> will be x-ray emissions.
> Unless I have got the wrong end of the coil, I mean we are talking about
> primary circuit, or do you mean a spark gap of of the secondary coil. If
> is the
> latter you may end up with a little particle accelerator and some
> when
> the few particles in the vacuum pick up high velocities and strike the
> electrodes;
> major x-rays!
> Regards,
> Gavin, U.K.
> Tesla List wrote:
> > Original Poster: "Alfred C. Erpel" <aerpel-at-pil-dot-net>
> >
> > Hello,
> >
> >     I am going to build a vacuum spark gap. I have a vacuum pump
capable of
> > 10^-4 torr. I have all the machine shop equipment, vacuum grade grease
> etc. to
> > do this properly. It will need to switch less than 500 watts.
> >     What non-mechanical issues might there be? X-ray concerns or any
> other type
> > of radiation? What percentage of energy might be expected to be
> by the
> > gap and/or radiated? What is the dielectric strength of a 10^-4 torr
> >
> > Regards,
> > Alfred Erpel
> >