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Re: theory(?) for long sparks [RSG]
From: D.C. Cox[SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: Saturday, November 29, 1997 7:59 PM
To: Tesla List
Subject: Re: theory(?) for long sparks
to: Greg
It appears this relationship is nearly linear. I have used a pulley
arrangement to belt drive a 12 inch dia RSG and also noted similar results.
It will be interesting to see if this holds true with the large sparks you
will be getting out of your 120 KW setup. Hope El Nino calms down but they
are already forecasting another bash to Tucson in the next few days and
probably will effect you as well.
DR.RESONANCE-at-next-wave-dot-net
> From: Greg Leyh[SMTP:lod-at-pacbell-dot-net]
> Sent: Friday, November 28, 1997 4:06 AM
> To: Tesla List
> Subject: Re: theory(?) for long sparks
>
> Jim Lux wrote:
>
>
> > I have just gotten my copy of "spark discharge" by Bazelyan and Raizer
(CRC
> > press). I have been inspired by the picture of the 100 meter+ spark
> > produced by only 5 MV, and have given some thought to what it takes to
make
> > long sparks.
>
> Me too... This has been my bedtime reading for the last week.
>
> > It appears that a spark propagates at around 2-3 cm per microsecond. If
the
> > voltage pulse producing the spark only lasts 10 microseconds, the
maximum
> > spark length that can be developed will be in the area of 20-30 cm.
> >
> > What is necessary for the spark to start is that the field at the
starting
> > point be greater than the breakdown for air (i.e. around 30 kV/cm).
Then,
> > for the spark to propagate, the voltage has to increase enough to cover
the
> > drop along the spark, and, the source has to supply sufficent current
to
> > "fill" the spark channel with charge. (I am doing horrible injustice to
the
> > pretty complex physics here, sorry).
> >
> > So, then, if you want to produce a 100 meter spark, (i.e. 1E4 cm), the
> > voltage has to be there for at least 5000 microseconds, and probably
> > longer. Further, the voltage has to be high enough to overcome the drop
in
> > a 100 meter long spark channel, i.e. several MV.
> >
> > A tesla coil running at 100 kHz (for example), has a half period of
only 5
> > microseconds, well short of the desirable 5 milliseconds. It is
possible
> > that the fine structure (i.e. the 100 kHz carrier) isn't the
significant
> > thing, but rather the overall envelope (i.e. the time til the first
> > "notch"), which would be more consistent with the observed 1-3 meter
length
> > sparks from a medium sized tesla coil.
> >
> > Ideas anyone?
>
> TC's may be able to effectively do better than the 2-3 cm per
> microsecond
> limitation, owing to the ion persistance between gap firings. Case in
> point:
> my DC coil will produce 3-4' streamers below 100PPS, ~10' streamers at
> 200PPS
> and 20-25' streamers at 350PPS. The primary cap voltage is the same at
> all
> gap speeds.
>
>
> -GL
>
>