From: "Malcolm Watts"
Date: Thu, 6 May 2004 08:48:01 +1200
Subject: Re: [TSSP] A naive question about discharge elongation
Hi Marco, On 5 May 2004, at 9:55, Marco.Denicolai@tellabs.com wrote: > Hello all, > > After reading all the references gathered from some of you, > iteratively the references of these papers, several HV books, > articles, etc. I feel I know something more but I am sure there is A > LOT I don't know yet. > > There is material about positive discharge, negative discharge, > corona, always with AC or single, more or less standardized pulses. I > found very few relevant data about elongation of AC discharges with > freq. of the order of kHz. Nobody seems to have bridged a 3 m gap with > only 600 kV (as Thor and typical TC do). I have began to think that: I personally know one experienced coiler from LA who had a pretty good grip on things being most uncertain as to whether he had ever reached 1MV despite running a coil which threw 25 footers. I do not think you are alone. > - AC with high freq. (kHz) can bridge longer gaps than a single > positive pulse (with crest voltage = peak AC voltage) - there is no > study of AC discharge as a succession of a negative and positive > discharges, analysing the static charge left and explaining the > elongation mechanism. > > What is your opinion? In a sense there is HF repetition present as the spark propagates on each successive half cycle within a bang. We are talking air streamers here. Once the streamers connect with a target, the Q of the system dives in a major way and that particular repetitive element disappears leaving only the bang repetition to repeatedly connect with the target. I came to these basic conclusions in '94 while doing the research for my article although at that time, I didn't fully realize the part that a still highish Q while streamers remained unconnected might play. Having said that, I am fully cognisant that what I've just said includes an element of handwaving and those whose expertise lies in gaseous discharges might have more quantitative things to say about this. But the Tesla coil differs greatly from a static source because of its HF oscillations. I think lightning probably comes close through its stepped leader and charge pooling mechanisms. > Did I misunderstand this phenomena here or...? > Is the TC long discharge mechanism analysed, modeled and known in the > literature or isn't? Any references were this is done? I am sorry I have not quantified my thinking to that degree but I am happy to see that the basic conclusions I reached 10 years ago are starting to withstand much deeper scrutiny. The key to understanding how sparks propagate in a TC system started coming to me when I realized the true magnitude of the voltages that could be reached (i.e. the scientific maximums) and then realized that rhapsodic notions I had read about the (disruptive) system ringing up and up while sparking were in fact myths. As always, the scope told the true story and I began to wonder why (at least some) others with oscilloscopes had not observed what I was clearly seeing. Malcolm
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.