Re: vacuum spark gap

Tesla List wrote:
> Original Poster: "Alfred C. Erpel" <aerpel-at-pil-dot-net>
> I was thinking that a vacuum gap would be the most responsive (and possibly
> the most efficient?) . I don't really see any meaningful difference in the
> effort it would take to make a high vacuum sealed gap and a pressurized gas
> gap.

	Think there is a very fundamental difference, namely that the "high
vacuum sealed gap" WON'T WORK AT ALL!  The gap in air or other gas,
pressurized or not, depends on the fact the air, once ionized, forms a
very low resistance path between the terminals.  In a high vacuum the
most that would happen would be ionization of the residual gas,
resulting in a low-current discharge, or field emission from the
terminals, resulting in a very low electron  current flow.  Note that
typical vacuum switches insulate 30 kVDC with spacings of perhaps
1/16".  At least some of the ones I have seen (but don't have,
unfortunately) have mechanical actuation of the moving part.  With one
of those you could move the contacts closer and closer together until
something happened, then observe the effect.

	Vacuum capacitors rely on the extremely "high dielectric strength" of a
vacuum to permit rather large capacitances in small devices.  The
typical plate spacing is only of the order of 0.010" and that will stand
off as much as 15 to 30 too.