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RE: spark gap ?

>Original Poster: Mark Finnis <mefinnis-at-medicine.adelaide.edu.au> 
>At 06:59 4/09/98 -0600, Gary Lau wrote:

>>I think you know the answer now.  If you have no airflow, it's like
>>asking "Will a 4 or 8 cylinder engine deliver more HP, even though I
>>don't put oil in it?"  If you are determined to not use airflow, Terry
>>Fritz has shown that gaps with a large number of very small spaces work
>>well.  Gaps with 10 or fewer segments run TERRIBLY with no airflow,

>Don't know that I would entirely agree with this.  I have a lot of respect
>for Terry's work & build one of his gaps (TFG) shortly after his original
>post.  This certainly produced an improvement over the 4-gap large-diameter
>copper tube arrangement I had at the time.
>
>Unfortunately this self-ignited as I had the rows of copper tubing too
>close together (was > 2x total series gap for the row, but you have to
>remember field concentration at the ends and adjacent surface effects !!!).
> Just a design point subsequent builders might want to keep in mind !
>
>The real problem I had was fouling between the gaps, and from subsequent
>posts I was not alone in this area ;-)
>
>My subsequent/current gap has only *3 stages*, and even without airflow
>this worked significantly better than the TFG.  This used tungsten TIG
>electrodes and LOTS of heat sink.  3 gaps were chosen by chance ..... I
>bought their complete stock ;-)
>
>Conclusion ........ it ain't *that* simple.  I have been playing this game
>for only 4-5 months (ie. complete bloody novice) but have realized there is
>a lot of science in spark gaps !

>>you should remember that airflow should be channeled THROUGH the gap arcs
>>as much as possible.

>Recently finished the forced-air part of the gap & this certainly improves
>performance, but to a lesser degree than going from a TFG multi-gap to the
>current one *without airflow*.
>
>Both gaps can be seen at
>
>	http://www.cobweb-dot-com.au/~dkfinnis/photos.htm
>
>I strongly suspect that using a material, or providing an environment (eg
>argon), which limits metal-oxidation is highly desirable.
>
>My 2c worth .......


Hi Mark:

As you say, my suggestion that the TFG is superior with little or no airflow
may not be true for just any coil, and I haven't tried it myself.  It may
be that a TFG works best only for small or low current coils.  I think
you're using a 15KV/120mA power supply, right?  I believe Terry used a
15KV/60mA power supply, but I think he also had to throttle it down with
a variac so as not to set his room on fire, so his results were probably
at a much reduced current level compared to yours.  (Terry, feel free to
chime in here...)

<<<< I do use a 15/60 neon.  We tried two of them (15/120) and the gap
really did need some sort of forced air for runs of 30 seconds or more.
Apparently, some are running up to 4KW through them with forced air and
good results.  Quench needs to be on the first notch to dramatically lower
dissipation.  Of course, there are other factors that may affect a
particular coil's performance.  - Terry >>>>


It's interesting that you saw superior results when going from a copper
tubing TFG to a 3 gap tungsten TIG electrode configuration.  Perhaps the
gap material selection is critical, not only in it's ability to resist
fouling and errosion, but also in it's property of not generating hot
ions which work against quenching, something I've not seen mentioned before.
It could be that if the gap material doesn't spew metal vapor, there's
less need for a fan to remove it, and this may provide a means of
significantly advancing the state of the art of spark gaps.

Regards, Gary Lau
Waltham, MA USA