RE: THOR Bang energy vs. streamer length measured

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

Original poster: "Denicolai, Marco" <Marco.Denicolai-at-tellabs-dot-com> 

Hi Jim,

How do you say there, "opening a can of worms"?

 > This is quite fascinating.  When you're measuring the
 > current, is it at the base of the leader?  Here's a sort of
 > conceptual model.  the spark channel is an ever growing
 > transmission line (that grows in jumps).  The charge has to
 > propagate down the currently existing channel (keeping it hot in the
 > process) to the tip, where the field steadily increases until
 > breakdown occurs.  Then, a short new segment is added, with
 > charge flowing into it (mostly from the end of the channel).
 > At some point, though, the voltage at the base starts to
 > decrease, and charge will eventually flow out of the channel
 > and back to the base electrode.

Les Renardieres group has documented (for breakdown due to a single
pulse in long gaps) positive leaders, negative leaders and even space
leaders (i.e. leaders born in the middle of the gap, not attached to the
anode or neither the catode). All these come and go, appear and disapper
during a *single* pulse breakdown. So, not even a TC bang, which is made
of a burst of pulses and therefore more complex, is needed to have this
mess to happen :)

Now, the leader-streamer mechanism is probably a simplification of the
problem (for long gaps) but, still, a very good starting point for this
matter in which all the scientific community is still very ignorant
indeed. Recall also that the leader-streamer mechanism won't be employed
for gap shorter than 1 meter.

 > As you say, positive polarities have lower breakdown voltage
 > than negative, so the time from zero crossing until new jump
 > occurs should be lower for positive than negative, BUT,
 > there's less charge in the channel when breakdown occurs, so
 > the length of jump might be less.

The static charge accumulated influences here, I don't only know how.
Corona inception voltage of a gap with alternating positive and negative
pulses has never been investigated (as for the accumulated charge and
its effect).

 > A H
  transformer that can be driven by a high power RF source
 > might be quite useful to investigate this, because you could
 > change the RF frequency (ideally on a cycle by cycle basis,
 > as with an arbitrary waveform generator), which would change
 > the relative timing of the channel conduction, leader jump,
 > etc. processes.

That would be nice to try.

 > One really needs a very high speed camera synchronized to the
 > RF, but, perhaps suitable high speed current measurements and
 > some carefully chosen efield measurement points might help.

We ordered one 5000 pictures/sec digital B/W from Ukraina. I suppose
it's only a matter of time to get it.

Best Regards

-