From: Bert Hickman
Date: Mon, 28 May 2001 01:12:55 -0500
Subject: Re: [TSSP] Genetic optimisation (New: temperature sensitivity!!)
Paul and all, I think we kind of all "assumed" that large numbers of residual ions were necessary, but because of recombination and thermal dissipation during the relatively long time period, we couldn't account for the observed behavior between bangs. Sometimes mining the older texts can unearth real gems! The reason for the decrease in breakdown voltage is indeed the longer mean free path. Electrons have more time to gain kinetic energy from the applied field, so at lower gas density, a lower applied E-field can now support initial ionization and avalanche breakdown thresholds. Paul wrote: > > Bert, All > > Some remarkable observations there from Peek's work. I never > realised there was such a sensitivity to temperature. I'm probably > not alone in having assumed all along that a fairly high temperature > would be required to memorise the passage of a streamer. > > Presumably the mean free path is longer at the lower density > associated with the higher temperature? > > > It's beginning to look as though we may have pinpointed the > > mechanism underlying bang-to-bang leader growth at relatively > > low break rates! The previous leader leaves behind a high > > temperature, lower density region having lowered dielectric > > strength - the NEXT leader can reignite at a significantly > > LOWER terminal potential, further extending the overall > > leader length over a series of sequential "bangs"! > > That's quite an important statement! It does sound very > plausible, given what you've reported from Peek. > > Does this mean that if a series of video frames from, say, ten > consecutive bangs where captured synchronously, they would be > expected to show the streamers developing further along each > path with each frame? I suppose the first bang would reach > the highest terminal voltage, and subsequent bangs would shunt > more charge into the streamer loading than earlier bangs, and so > would reach progressively lower peak voltages. Yes. Frame-to-frame growth has been observed in numerous videotapes and by observation of operating coils. Unfortunately, unless one is using a SRSG or DC Coil to generate uniform bangs, bang size variations may cause the leader to grow or shrink from one bang to another once a certain minimal length has been achieved. It may be that the uniformity of bang size is why SRSG systems seem to generate the longest leader length with respect to input power. Many of the videotapes produced by Richard Hull and John Freau clearly show streamers growing over time, sometimes using the same "root" for one or more seconds at a time. BTW, there are some other measurements that you may be interested in reviewing. When Greg Leyh was testing Electrum in 1998, he was able to make measurements of current between the top of the resonator and the top sphere, and from the sphere to streamers/leaders. Greg did this by means of Pearson wide band current transformers while he and the measurement equipment were inside the topload! These measurements were taken at 2 uSec, 5 uSec, 10 uSec, 20 uSec, and 100 uSec/division, and clearly show current spikes during leader propagation, and displacement currents out of, and back into, the topload once leaders were formed. Greg's measurements can be seen at his site: http://www.lod.org/electrum/sphere100us.jpg http://www.lod.org/electrum/sphere20us.jpg http://www.lod.org/electrum/sphere10us.jpg http://www.lod.org/electrum/sphere05us.jpg http://www.lod.org/electrum/sphere02us.jpg For example, in sphere20us.jpg, precursor current spikes can be seen, leading to fairly heavy negative current being pulled out of the surrounding space charge region at about 40 uSec. This is then followed by a much larger positive current peak (a positive leader) at 50 uSec which is then kept "alive" by relatively steady displacement arc current as charge is first transferred into and then pulled out of the leader during the subsequent negative transition. This is followed by an even higher amplitude current peak at about 80 uSec as the NEXT positive half cycle as part of the negative space charge around the streamer (from the previous negative half cycle) is neutralized and another (higher current) extension to the leader occurs. A smaller spike can also be observed at about 105 uSec. The overall leader length at full power was about 50 feet. There are lots of other interesting things that can be gleaned from these invaluable measurements! > Perhaps in lieu of a synchronised camera, a light curve could be > obtained with some kind of photodetector? > > Cheers, > -- > Paul Nicholson, > Manchester, UK. > -- Lots to ponder... Best regards, -- Bert -- -- Bert Hickman Stoneridge Engineering Email: bert.hickman@aquila.net Web Site: http://www.teslamania.com
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.