Re: [TSSP] THOR: First observations on streamer formatio

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Marco,
           I'm glad you're managing to get around to doing these expts
with this particular setup. It was the same approach that I wanted to
take but time just hasn't been on my side and the inverter design is
in mothballs at the moment.

On 11 Mar 2004, at 8:47, Marco.Denicolai-at-tellabs-dot-com wrote:

 > 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<<

I don't think this is particularly surprising either. I have observed
this many times and the most striking demo I saw was single shot
testing of Electrum at its final home. The impression burned into my
memory was of it producing a single-rooted streamer which branched
into a tree with a visible length of about 7' at its breakout energy
(Vp about 35kV).

      I've said this before but Tesla speculated in some of his early
notes that the many sparklets and tendrils one sees must each have
been due to a single cycle of oscillation. Of course we know today
that this cannot possibly be true since there are so many of them as
compared to the relatively few oscillations produced by a single shot.


 > 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.

Other useful information could come from the following combinations:

- different sized terminals with the same ROC and a suitably retapped
   primary with Ep remaining constant. This would tell us something
   about the balance between terminal storage (total Cs) and output
   voltage at different breakrates.

- As above but this time with energy increased with terminal size to
   keep Vout constant.

- Constant Ep and ideally terminal capacitance but with ROC varied.

I will present more possible scenarios as they come to me. Thanks for
doing this work. I am delighted that you are in a position to be able
to do some of the tests I for one have thought about for so long.

Regards,
malcolm