Re: [TCML] voltage

[Paul Nicholson <tcml88@xxxxxxxxxxx>]

Bob Svangren wrote:

> ...  the 20KV volts per inch standard,

Sorry, it won't work.

> A 50 inch arc would equal a million volts.

Really, the voltage is far less than that.

It's the local field strength at the tip of the streamer that
causes it to extend, therefore the terminal voltage doesn't
have the simple proportionality to arc length that you're
looking for.

The streamer tip - guided as it is by the field strength in its
vicinity - moves like a mountaineer coming down off a hill in
a dense fog who decides to always take the steepest direction
downwards.   This method often doesn't produce the shortest
path to the valley.   Similarly, the shortest path from the
toroid to earth is directly down the secondary, but the field
gradient around the toroid is steepest at the toroid's outer
rim and this fools the streamers into developing outwards from
this point.  Then in a succession of very rapid small steps
the streamer tip advances, always looking for the 'steepest
descent'.  It'll continue outwards so long as it sees a local
gradient of 24kV/cm or so - which is quite easy to obtain from
the sharp point of a thin streamer.    There just needs to be
enough charge in reserve on the toroid to flow out along the
streamer and keep the tip at a high enough local field strength.

There won't be much voltage difference between a toroid just
starting to break out and one that is developing long arcs,
so the proportionality scheme fails rather badly.

To produce long streamers, really the coil just needs to
develop enough voltage to start the breakout, and then be
able to back that up with plenty of charge (ie a big toroid)
and enough power to keep the streamers hot and low resistance.
Therefore you're more likely to find a simple relationship
from input power * efficiency to arc length.

As for the top voltage, it will be roughly clamped at the
voltage where the surface field strength on the outer rim is
enough for break out and that's mostly a radius of curvature
thing, independent of the details of the coil below it.
I think as you try to drive the voltage higher, more streamers
emanate and so the loading is increased and this provides a
clamping effect.

There is much to be done to quantify these things and the field
is wide open for someone to thoroughly instrument a coil and
measure what's going on.   Of course, that needs a top voltage
measurement, which is where Charles Van Neste is.
--
Paul Nicholson
--
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