Re: Spark Dissipation

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

Original poster: "Gary Johnson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <gjohnson-at-ksu.edu>

At 11:44 AM 02/01/2001 -0700, you wrote:
>Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<FutureT-at-aol-dot-com>
>
>In a message dated 1/31/01 10:14:43 PM Eastern Standard Time, 
>tesla-at-pupman-dot-com writes:
>
>> It appears that the second spark might try to follow the path of the first
>>  one for a short distance (an inch or less) but then finds its own path. Two
>>  distinct sparks were evident most of the time, even at a spacing of 2 ms. 
>>  
>>  At 125 sparks per second (5 ms burst and 3 ms spacing) the
>>  spark length drops about 12 percent from the 1 spark per second case. There
>>  are enough other things happening in a conventional Tesla coil (resonance 
>in
>>  the power supply, heating effects, etc.) that this probably would not be
>>  obvious either. The point is that one should use whatever break rate gives
>>  the most pleasing visual appearance, without expecting that going from 60 
>to
>>  120 to 240 sparks per second will make a significant difference in spark
>>  length.
>>  
>>  Gary Johnson
>
>Gary,
>
>Do I understand correctly, that you're suggesting disruptive spark
>lengths do not increase much as the break rate is increased from
>for instance 120 to 240 bps?  This does not seem to fit what I've
>seen in my work.  I've found a 20% increase in spark length as
>the bps was increased from 120 to 240 bps while keeping the
>bang size constant.  Greg Leyh's streamers in his old coil, 
>grew almost linearly with increased breakrate.  The sparks can
>be seen to grow over time.  The sparks from each bang do not 
>seem to be separate sparks, but seem to follow the same paths,
>adding to the length.
>
>John
>
Hi John:

Yes, John, I am familiar with your work.  Perhaps I generalized too much,
implying that results for 6 inch sparks from a solid state driver would
apply for 50 inch sparks from a spark gap system. I think we are both
reporting accurately what we see in our labs. The fun part will be to
isolate exactly what is causing the difference, why I can't extrapolate up
and you can't extrapolate down. One advantage of a solid state system is
that I can have exactly two sparks in quick succession, followed by a long
gap. The first spark always starts in air with a low ion concentration. With
a spark gap, you have 120 or 240 sparks per second, say, so the ion
concentration must be higher. That is an obvious candidate for the possible
cause of the differences.

I know this: for my system with two sparks as little as 2 ms apart (and then
1 second before the next two sparks), I clearly see two sparks. They appear
to start at the same point on the brass knob and may share the same path for
the first 10 percent of their length. I look at the spark at one per second,
and then at this doublet once per second, and do not see any increase in
length, just two sparks of the same length as the one.

I also note that the spark length for CW operation is less than the spark
length for one per second, at a given applied voltage.  I am not sure how to
describe the break rate for CW operation, except perhaps at a limit or
maximum value, something higher than 240 bps. I think I am seeing a
monotonic decrease in spark length as break rate goes from 1 to some maximum
value per second. I don't know if you can increase the break rate for a
disruptive coil to where it approximates CW operation, but if that were
possible, I would predict that spark length will hit some maximum for a
given break rate and then start to decline for higher break rates.

Isn't this stuff fun?

Gary Johnson