Re: Static gap behavior

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 05:52 PM 1/12/2004 -0700, you wrote:
>Original poster: "C.T." <ct451-at-yahoo-dot-com>
>I'm using two horizontal 4.5" pieces of 1" copper pipe as a gap on a small 
>coil running on a 4000/30 NST.
>The gap is too small <0.05" apart and I only get 6-7" streamers on the top 
>but I noticed a peculiar behavior while the coil is running.
>The actual spark  will only be ~3/4-1" along the length of the pipe but it 
>starts on one end and slowly moves up length of the pipes over a number of 
>cycles (or so it appears to the naked eye).

Do you mean that the "sparking area" along the pipe is about an inch long? 
(so it looks like a bright band between the pipes?)

>When it reaches the end it will either turn back and come down the 
>opposite direction or jump to the other end and start moving forward again.
>
>More ionized gasses at the side of the previous spark or something I'd guess.
>Is this normal behavior for this type of gaps or has anyone observed the 
>same? How does this affect the performance of the coil?

I've noticed the spark moving along the length of my copper pipe gap when 
running without any airflow.  A low speed blower (little muffin fan) makes 
it apparently random, so I suspect it's a local heating effect, whether of 
the air or the electrode material, I don't know.  Both would affect the 
striking behavior.


>Also I was wondering if there's a rule of thumb or a table somewhere that 
>gives approximate breakdown voltages for gaps with cylindrical electrodes.

If the gap is much less than the diameter of the pipes (which yours is), 
you can probably consider it as a uniform field gap.  A number like 70 
kV/inch will be in the ballpark (10% or so).
Your 0.05" gap would be be about 3.5 kV.




>any input welcome,
>Chris
>