Re: On sparks

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>

>
> There are some interesting energy insights here...
> The E-field and base current measurements imply that it takes a
> comparatively large amount of energy to initially form the leaders versus
> the amount required to maintain them (at least for near CW operation).

This is pretty much to be expected... once the spark channel is established,
the resistance of the channel drops, so you don't need as much voltage to
keep the charge flowing fast enough to keep the leader head moving.  I
suspect that the leader head only moves on one polarity of the RF, and that,
during the other half, the charge is flowing back down along the spark
channel (keeping it hot).  However, there's no question that more voltage,
if not more energy, is going to be required to form the channel in the first
place.

The "optimum" long spark waveform might be a big spike at the beginning (to
cause breakdown), and then substantial low impedance current to flow along
the leader.  The end of the leader is pretty "pointy" so it probably doesn't
take much voltage to create a big enough field there to keep the breakdown
going, especially compared to the "top load" which has a big ROC, and needs
a fairly big voltage to even start to breakdown.

An interesting thought here.. If the topload breaks down too early, not
enough charge will be stored to support the leader growth, so you kind of
want a big smooth topload so that it can accumulate enough charge to support
a big long spark.  However, given that you can transfer charge into the
topload on every cycle of the RF, with the right circuit, a breakout point
(to force earlier breakdown), combined with the right tuned circuits, might
work even better.

The whole thing reminds me of a "peaking gap", as used in impulse testing.