[Prev][Next][Index][Thread]

Re: A Puzzle


From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Friday, September 05, 1997 9:15 AM
To: 	Tesla List
Subject: 	Re: A Puzzle

Tesla List wrote:
> 
> From:   Richard Wayne Wall[SMTP:rwall-at-ix-dot-netcom-dot-com]
> Sent:   Thursday, September 04, 1997 1:50 PM
> To:     Tesla List
> Subject:        Re: A Puzzle
> 
> Bert wrote:
> 
> snip
> 
> >> >The current levels required to support streamer growth are in the
> >> >multi-ampere range.
> >>
> >> snip
> >>
> >> Bert, have these current levels been experimentally measured and
> >> validated in the multi-ampere range?
> >>
> >> RWW
> >
> >Richard,
> >
> >Yes. There's actually quite a large body of research that's been done
> >in the area of long-spark "arrested streamers" over the years. These
> >experiments typically use a high voltage impulse generator (usually a
> >triggered Marx Generator) connected to a rod-plane (non-uniform field)
> >test gap.
> 
> snip
> 
> So, actually all these "arrested streamer" experiments were *not* done
> with quarter wave air resonate coils?  And, the streamers and arcs
> looked like and were dead ringers for Tesla coil discharges?  So
> naturally it follows that experimentally measured discharge currents in
> nonresonate nonquarter wave systems extrapolate to Tesla coil discharge
> currents.  I would submit that these discharges probably resemble van
> deGraf generator sparks also.  Incidently, Van deGraf generators
> produce exceedingly low current discharges.  (Actually, TC discharges
> are much like Van deGraf discharges, ie., very low current.)  As we all
> understand, voltage in a tuned quarter wave resonator reaches its
> practical maximum and current approaches zero in the limit at the top
> termination.
> 

Unfortunately, the mainstream scientific community hasn't done very much
experimentation using Tesla Coil voltage sources. While some high
frequency discharge research is also available, most modern day work
tends to be mostly microwave excitation of plasma for fusion and plasma
cleaning/processing. Richard, ALL long sparks (not arcs...) tend to look
fairly similar irrespective of their origin. 

However, as to sparks from TC's or VDG's being low current, you may be
confusing things abit. A Van deGraaff generator may have only
microamperes of charging current. A TC at its's first voltage peak may
have NO current flowing into the toroid from the resonator. However, in
both cases, there will be substantial energy available in the charged
top terminal capacitance and the surrounding ion space charge. A charged
capacitor of any type will deliver high currents very quickly - the
lower the discharge path inductance and spark resistance, the greater
the current flow. Spark breakdown, when driven directly from this type
of source, will deliver quite large currents, if only for a brief
instant. 

> snip
> 
> >I happen to use a 25 watt tubular bulb, but a regular style light bulb
> >will also work as well. When the coil is running at full power, the
> >bulb is lit by the streamer currents forced to flow thru the bulb and
> >"into" the air.
> >
> >By comparing the degree of brightness with an identical lamp driven
> >from a DC source, I found that this corresponds to about 110 mA of
> >"average" current.
> 
> snip
> 
> Again, very subjective measurements.  The eye, as well as, the ear are
> nonlinear detectors.  Also, the intense electrostatic field at the TC
> termination causes ionization of gases and illumination in light bulbs.
> This will introduce noncurrent error, particurally in a visual
> detection system.
> 
> A much better method is to use a "current driven device" such as a LED.
> Dwayne Bylund has demonstrated very low curents associated at the top
> of a resonator coil with serial LEDs along the coil.  RH has an
> excellent video tape proving that LEDs have good frequency response in
> the range of most TCs.  An LED coupled to a fiber optic cable will
> detect TC current above its threshold.  The signal can be calibrated
> and compared to a known current value.
> 
> RWW

A light bulb IS a current driven device. and is almost ideal for
integrating the type of rapid, fast rise-time current spikes associated
with streamer propagation (as long as the current doesn't take a "short
cut" and jump around the inductance of the filament). And the bulb is
operated in the "shielded" region of the top toroid, so ionization
heating is not a factor. I am familiar with Duane Byland's LED's in
various places along the resonator.. note that these will NOT permit you
to measure the peak currents coming off the self-C of the charged toroid
itself. Further, while the frequency response of LED's is not bad
relative to a couple of hundred kilohertz, accurate measurement of
current peaks going into discharges off the top would require much
higher bandwidth than available with common LED's. 

While I might not be able to pick out the peaks using a tungsten
filament, I have no doubt that the average current measurements are in
the ballpark. Any thoughts from other coilers?? Are the hot discharges
coming off big coils only demonstrating milliamp or microampere current
levels?

Safe coiling to you!

-- Bert --