Re: Spark-gap sparks vs. solid-state sparks

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>

Malcolm and all,

Glad to hear I'm not the only one who's seen this! I suspect that few
coilers have actually observed this because the required conditions are
somewhat unique. First, the coil and topload must be near the verge of
breakout, but the topload must not actually break out. The light from the
main gap should be shielded so that the dim corona and streamer flashes can
be more easily observed. And, while it's not essential for your eyes to be
dark-adapted, it helps considerably when trying to observe the faint outer
region of the discharges. I accidentally stumbled upon this phenomenon
while making a change to a larger toroid, and the system then no longer
achieved breakout. After seeing something strange (the outer portion of the
toroid was sort of "glowing"), I then purposely reduced the light to see
what was really going on. I couldn't believe the level of activity that was
going on around the toroid - it was surprisingly bright and quite
beautiful!

There's some evidence (again via Bazelyan) that corona and streamer flashes
represent mostly a capacitive load to the HV electrode, and that current
may not only be "injected" into the surrounding region when the topload is
positive, it may also be "extracted" from the surrounding space charge when
the topload polarity reverses, returning some of the surrounding space
charge back to the topload. If this is primarily a "reactive" transfer, the
impact on Q would be minimal, while still impacting Fo of the secondary...

-- Bert -- 
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>
> 
> Hi Bert,
> 
> On 23 Apr 01, at 8:00, Tesla list wrote:
> 
> > Original poster: "Bert Hickman by way of Terry Fritz
> > <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>
> >
> > John, Ken, and all,
> >
> > John, I believe you are correct. Have you watched (in a completely
> > darkened room with dark-adapted eyes) a coil operating just below the
> > point of streamer breakout? For a disruptive coil topped with a toroid
> > of large minor diameter, the outermost surface of the toroid (the
> > region of highest E-field) is bathed in a diffuse bluish glow. Upon
> > closer examination, it can be seen that this glow actually consists of
> > countless bush-like discharges. Technically called streamer corona and
> > coronal flashes, these are "cold" discharges that are the predecessors
> > to true leader formation (or "breakout"). As the coil operates, these
> > individual flashes constantly flash and wink out of existence, being
> > brighter at the toroid surface, dimming as they extend outward to the
> > limits of visibility. On my system, the visible portion of these
> > discharges extend outward by as much as 12-18" (versus 65" leaders
> > after breakout occurs). At this stage, the overall average current
> > flow is low if compared to that of a fully formed leader, but it is
> > NOT zero. In fact, per Bazelyan ("Spark Discharge") the peak currents
> > of these coronal flashes may actually be in the ampere range but
> > individual discharges may last only tens or hundreds of nanoseconds.
> >
> > Each of these discharges effectively transfers an increment of charge
> > from the toroid to the space charge in the surrounding region. This
> > would appear to the topload as an additional resistive and capacitive
> > load as charge is injected and removed from the surrounding region
> > during polarity reversals of the topload. Paul's latest TSSP model
> > (Section 2) indicates that even small resistive loading tends to
> > reduce resonator frequency. Perhaps the combination of the additional
> > capacitive loading and energy loss through these cold discharges
> > account for the observed frequency shifts prior to the more obvious
> > added capacitance of fully formed leaders...
> >
> > -- Bert --
> 
> I have seen exactly that on one occasion. I was not expecting it. I
> observed a ball of wispy streamers about 3' or so in diameter
> emanating from a 9" sphere. At first I couldn't believe what I was
> seeing. This must be the source of the pre-breakout C and shunt
> resistance. This resistance is high though. Scoping the e-field shows
> Q dropping by very little.
> 
> Regards,
> malcolm
> <snip>