From: Paul
Date: Fri, 27 Sep 2002 18:33:24 +0100
Subject: Re: [TSSP] Top Voltage
Terry wrote: > Good news. The fiber probe seemed to be working most of the > time so the previous data is fine. Well that's good. Those current signals looked too realistic to be an artifact. Hope the current probe is fit for battle. Bert wrote: > Corona, and corona flashes (or streamers) are all "cold" > discharges, while leaders (what most coilers mistakenly call > streamers) are composed of hotter, highly conductive plasma > (actually more arc-like). So the leaders are plasma, but the streamers are un-ionised gas with the odd accelerated electron, insufficient in themselves to cause a bulk ionisation of the air, but enough when combined in their multitude to cause a leader to form? You see, in the back of my mind, I'm forming a hypothesis that Terry's topload is in fact breaking out rather earlier than the load current probe suggests. Could it be that streamers are forming at around the expected breakout voltage, but a) they are not bright enough to see, b) their large number plus their individual miniscule current adds up to a smooth average displacement current which is sufficiently smoothed by their large number to be indistinguishable from the displacement current that we can already see charging the rod and sphere. Perhaps the spikes we are taking to indicate breakout actually mark the formation of distinct, visible leaders, and that a much less visible (by eye or current probe) breakout is starting rather earlier. Malcolm has in the past reported a faint glow around his topload prior to obvious breakout. If this hypothesis were correct, then if we measured base current and rod+sphere+load current simultaneously (average or RMS values here, not scope traces) and plotted their ratio as a function of variac setting, then we would see a departure from a constant ratio. At low power, definately no breakout, the value would be set by the fixed capacitance of the rod+sphere. As the voltage is turned up and invisible streamers begin to form, the load current would increase disproportionately above the base current. Conveniently, Terry's rod+sphere is of quite small C, therefore it should be fairly sensitive to a small additional streamer current. > http://www.physic.ut.ee/~tomas/phd_plank.pdf Thanks Bert. www.physic.ut.ee is not letting me download at the moment, I'll try again later. I'm away this weekend at the final round of the British rally championship, so if anyone posts anything, don't worry if it doesn't come through until Sunday. Cheers All, -- Paul Nicholson, --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.