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Re: Primary Qs

Tesla List wrote:
> 
> >From MALCOLM-at-directorate.wnp.ac.nzTue Oct  1 21:55:47 1996
> Date: Wed, 2 Oct 1996 09:03:02 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Re: Primary Qs
> 
> Greg,
>       Thankyou for this info....
> 
> > > Q does trend up with increased gap current showing a drop in gap
> > > resistance. It would be useful to get readings for much higher
> > > voltages but the supply and caps on hand wouldn't allow it.
> >
> > This observation would agree with the data from 'Gaseous Conductors',
> > where the author noted that the current *density* in an arc remains
> > relatively constant as the gap current is varied.  This would mean
> > that if the gap current were doubled, then the arc cross-section
> > would roughly double, cutting the resistance by half.
> 
>      I wonder if the current density then relates to the number of
> potential current carriers (npi) present (e.g. gas molecules) in a
> given cross-sectional area? I wonder if your pressurized gap at 3 atm
> (?) would allow a much higher current density than we get at normal
> air pressure? Also, would blowing compressed air through the gap have
> a similar effect? If this were true, it would seem that pressurized
> gaps are more efficient than normal air pressure. What do you think?
> Anybody measured this?
> 
> Malcolm
> <snip> point noted thanks. For the normal configuration of spark gap
> in my new machine I'm looking at using about 200uH primary with 50nF
> at 20kV peak. Those CP caps are looking wonderful right now. Thanks
> to Scott for organizing the purchase of them.

Malcolm,

All your logic seems correct about doubling the current carriers in the 
arc at higher pressures.  I do know that at higher pressures the gap 
width must decrease per unit voltage over atmosphere.  These generalities 
are pretty good, but not precise.  Equations are around that supposedly 
allow this breakdown to be computed. (in short conrolled gaps at fixed 
pressure.)  I have been reading a number of core level treatises on 
gaseous conduction. (and a few texts).  It seems everyone has the answer 
and they are all somewhat different.  I have become more and more leary 
of "the final word on the matter" theories about just what happens in a 
gap at break down.  The gross picture is relatively well understood.  It 
is the actual minutia that remains a mystery.

Richard Hull, TCBOR