Re: Streamers (and Ion Clouds...)

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

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

All,

My previous post apparently wasn't sufficiently clear: It's _Free
Electrons_ that last for an average of only ~11 nSec in air before
becoming attached to oxygen and water molecules, forming negative ions.
Once attached, these electrons are no longer free, and are effectively
taken "out of play". Attached electrons no longer support avalanche
breakdown and streamer development. 

There's NO doubt that both positive and negative ions last MUCH longer.
There's also evidence that ions can linger from previous bang(s), and
their numbers can thus increase during subsequent bangs. Finally,
there's also evidence that sparking Tesla Coils are prodigious producers
of ions. The point I was attempting to make (not very well I admit...
:^)) is that ions, per se, are not directly involved in the initial
stages of spark breakdown, so their presence is basically _irrelevant_
to breakdown processes at the beginning of a NEW bang. 

So... if we take uniformly cold air mixed with lots of positive and
negative ions, and compare it to uniformly cold air with NO ions,
breakdown would behave in a similar fashion! The presence of ions really
doesn't matter. You can see this situation if you run a system at high
breakrate (generating lots of ions!) and then significantly lower the
breakrate to permit channels to cool down between breaks - in this case
every bang then behaves independently with no channel followthrough from
bang to bang.

BTW, I had an offlist discussion with Gary Lau this morning about the
"ion cloud" that surrounds the topload of a sparking coil. Capacitive
loading from this cloud has been thought to create the observed downward
shift in the secondary's resonant frequency. I suspect the real answer
is a bit different, and that the presence of long lived ions around the
topload is not the root cause of the frequency shift. 

Instead, we are likely seeing the effect of displacement currents (via
leaders and streamers) into, and out of, the region around the toroid.
The exchanges of charge between the topload and surrounding region look
and behave much like an additional capacitance. Charge flows into, and
back out of, the region around the toroid via streamers and the rooted
leader, behaving as though we've added topload capacitance. The current
waveforms seen on Greg Leyh's system clearly show high frequency
displacement currents flowing into and out of a rooted leader, as well
as much briefer (10's of nanoseconds) current transients corresponding
to streamer flashes. 

These current transients can be seen heading both OUT of the topload,
and also back INTO it. These displacement currents behave (grossly) as
though we've added capacitance to the topload, lowering the secondary
system's resonant frequency. The presence of hot leaders may not even be
necessary - the additional capacitance should be observable as soon as
we begin generating streamers or streamer flashes (i.e., the dim
precursors to arc-like leaders).  

Suppose you were able to very quickly power down your system and measure
the secondary's resonant frequency using a base-driven signal generator.
You would not observe capacitive loading from the "ion cloud", since the
output terminal voltage is now too low to support avalanche breakdown
and the resulting streamers that create the loading effect - even though
the "ion cloud" may still be lingering. in the vicinity. That's not to
say that positive and negative ions don't exist, cloud like, around the
top of an operating coil - they do in abundance, for some time after the
coil is turned off. However, this "ion cloud" plays no direct role in
the observed frequency shift...

Best regards,

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

Tesla list wrote:
> 
> Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<davep-at-quik-dot-com>
> 
> Tesla list wrote:
> >
> > Original poster: "rheidlebaugh by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
> >
> > Bert: I like your posting and I intent to save it, but...I have
measured ion
> > life in liquids over 11 seconds and in air over several minutes. While the
> > center ion track time is limited to the browian movement time the
surounding
> > wide track remains for a long time like a static cloud.
> >   Robert  H
> >
> > > From: "Tesla list" <tesla-at-pupman-dot-com>
> > > Date: Sun, 24 Feb 2002 22:26:39 -0700
> > > To: tesla-at-pupman-dot-com
> > > Subject: Re: Streamers
> > > Resent-From: tesla-at-pupman-dot-com
> > > Resent-Date: Sun, 24 Feb 2002 22:36:49 -0700
> > >
> > > Original poster: "Bert Hickman by way of Terry Fritz
<twftesla-at-qwest-dot-net>"
> > > <bert.hickman-at-aquila-dot-net>
> > >
> > > Dave and all,
> > >
> > > I still suspect the main reason why leaders follow the previous channel
> > > from bang to bang is lower air density and not the presence of residual
> > > ions. The reason? Although longer lived positive and negative ions can
> > > indeed persist from one bang to the next, their presence does not
> > > directly contribute to the spark breakdown process on the next bang.
> > >
> > > Avalanche breakdown initially requires free electrons, accelerated by an
> > > E-field, colliding with air molecules, to create an increasing cascading
> > > shower of free electrons. For the avalanche to proceed, the rate of free
> > > electron creation must exceed the rate of electron loss through
> > > attachment (to oxygen or water vapor molecules to form negative ions).
> > > Electron attachment occurs very quickly in air. Any free electrons
> > > created during the previous bang are long gone by the time of the next
> > > bang, having been captured by electronegative gases in the air since the
> > > average "free" electron life in air at STP is only about 11 nSec.
> 
>         Lacking a site, other than the one to Cobine, previously supplied,
>         (which would take some work to reduce to 'real time',) i can
>         only say:
> 
>                 I think, for whatever reason, 'tis longer than that...
> 
>         Not real rigorous...
> 
>         (ferinstance:
>                 The 'inside' of a lighting bolt (or streamer) is
>                 unlikely to be AT STP.
>         )
> 
>         best
>         dwp