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Re: an interesting idea...



As the pressure decreases, the breakdown (sparking)  voltage changes until
you get to the "Paschen minimum" after which, lowering the pressure
actually increased the breakdown voltage.  Even in a very "hard" vacuum,
you can still get a spark, although the propagation and initiation
mechanism is quite different (because you can't get the cascading electron
emission you get at higher pressures). For one thing, you have to vaporize
enough electrode metal to form ions to carry the arc current. (So, I guess
it really isn't a vacuum any more).

Glow discharges and x-rays and similar phenomenon occur below the Paschen
minimum.

for more on Paschen Law: http://home.earthlink-dot-net/~jimlux/hv/paschen.htm

There is also corona, which occurs in areas of high field stress, but where
a breakdown can't occur. 

----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: an interesting idea...
> Date: Friday, May 21, 1999 5:19 AM
> 
> Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> 
> 
> Jim Lux wrote:
> 
> > And, no, air isn't required for a spark to jump.
> 
> But the breakdown voltage drops as pressure goes down,
> and the appearance of the "spark" changes too, becoming
> diffuse. At some point the breakdown voltage starts to
> rise again, and there is almost no visible light,
> but cathode rays and X rays production.
> I am really not sure of exactly what is the behavior
> at this point (I would have to read a bit). 
> Can someone post something more precise on how the
> behavior of a "spark" in air as the pressure drops?
> 
> Antonio Carlos M. de Queiroz
> 
> 
>