From: Paul
Date: Mon, 20 May 2002 15:02:31 +0100
Subject: Re: [TSSP] Racing arcs
I wrote: > If breakout limits that in reality to > 26kV/cm, the topload > will be limited to 960 kV * 26/50 = 500 kV Boris wrote: > No. Usually final voltage will be higher than that... > you are forgetting that SPACE charge around toroid will contribute.. Yes! I've completely ignored space charge, and that could alter the picture quite a bit. > Discharging only clamps max field at the > surface,but not voltage in such a drastical manner. Indeed. Space charge around the topload will reduce the surface field strength for a given topvolts. Therefore if the streamer dynamics acts to clamp the surface field at 26kV/cm, it will not clamp the topvolts if significant space charge is present. Topvolts will continue to rise causing more streamer-feet of charge to join the space charge as necessary to limit the surface to 26kV/cm. In that case, the topvolts still will not rise past the Vtop given in the web page tables, and nor will the coil surface fields rise past the values given in the animations, but it does reduce or destroy the usefulness of the 'breakdown ratio' that I defined in a previous post, which relied on perfect topvolts clamping. Instead, with space charge, the dynamics will apply only a very soft clamping to the topvolts - the V/Q curve will not have a sharp knee, but instead a rounded levelling off. The issue of space charge certainly complicates things! It's going to be even more interesting to see some accurate topvolts measurements from a breaking-out coil. I'll have to think about this development a little more. But one thing comes to mind - this should imply that the streamer roots on the topload will try to space themselves as far apart from each other as they can, because as one streamer forms, its addition to the space charge above that region of the topload will tend to suppress further new streamers in that area. Only away from that root will the surface field attempt to exceed 26kV/cm and start a new streamer. -- Paul Nicholson, --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.