THOR: First observations on streamer formation (try II)

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Original poster: Marco.Denicolai-at-tellabs-dot-com 

The first email was incomplete, sorry. Let's try again :)

Hello all,

I spent the last months designing, building and debugging a new
controller board to allow my bigger TC (named THOR, see
www.iki.fi/dncmrc) to perform a perdetermined number of bangs. Thor is a
disruptive TC: a SMPS charges the primary capacitor, synchronizing the
charge with the RSG electrode position and reaching a predefined
voltage. The new board allows to do this a predefined number of times,
as it can count the number of electrode presentations.

80% of the effort had to be put into a mixture of shielding, grounding,
filtering and optoisolation. Without this the board was prone to
misfunctioning due to the powerful transient generated by the bangs. I
was able yesterday for the first time to get rid of the noise and see
the new board work as it was supposed to.

The meaning of the setup was to investigate how bang size, bang
repetition rate and number of bangs influenced the growth of the
streamers. This is a question often asked in the list posts and the
answers are usually different, based on observation, speculation or
"measurements". For instance, I recall someone answering that he gets
full length streamers even with a single bang (!). Then there are the
explanations about ionized channel formation and its lifetime, etc.

Yesterday, as I wrote above, I was able to play with the setup for the
first time. I haven't got yet measurements and data but I still wanted
to share with you what I have seen.
I changed the number of consecutive bangs. With a single bang I got
about 15 cm long streamers. Increasing the number of bangs I got
increased length. At about 13-14 bangs I reached the full streamer
length, that is a grounded stick at about 3 meters from the toroid.

Nothing new here: this is what I expected to see. The surprising thing
was the behaviour with a SINGLE bang. I could see the formation of:
- a single streamer OR
- a biforked streamer OR
- at least two streamers from two different toroid locations

 >>This means that a single bang is capable of producing a number of
streamers, not just one<<

Next I'll have to decide what to measure and how. First ideas:
- current throught the grounded stick (with a Rogoski coil) when there
is no hit. Could it register the smaller streamers?
- current at the secondary bottom
- readings with Terry's old Voltage-current antenna
- run of statistical measurements bang_amount vs. streamer_length vs.
bang_voltage

Here your input and help is more than welcome. Also if you know/find
interesting references on high frequency streamer formation, dielectric
strength, etc. please, let me know.

Regards