From: Paul
Date: Fri, 30 Apr 2004 19:31:27 +0100
Subject: Re: [o-o] [TSSP] Modeling with ANSOFT
Marco, > I have still a lot of thinking/reading/measuring > before I can tell you anything valuable. It takes time... Have you anything with which to measure the operating topvolts of the coil, to the extent of capturing a calibrated waveform into a scope? To be useful, the measured signal would have to report specifically the toroid voltage and not just sample the E-field flux from the vicinity of the topload. This signal, combined with that from a coil-top current probe, would allow us to calculate the total streamer charge, as a function of time, through the breakout event. We have Q = CV for the topload and its breakout load. So the current into the topload from the coil is dQ/dt = CdV/dt + VdC/dt The measured signals give us dQ/dt, V, and dV/dt, so that we determine dC/dt and the 'breakout charge' VdC/dt as functions of time. If we just sample the flux, we get a signal roughly proportional to Q, which isn't very helpful. This is the point on which we are a bit stalled at the moment. Sometime ago we discussed the prospects of a shielded capacitive divider, perhaps running down inside the secondary. Sorry I'm not familiar with the commercial field modelling packages, so can't really help with that. But I think it would be easy if you just model the system with charged rings, discs, toroids, spheres, etc, and set them to appropriate voltages (eg Terry's voltage distributions). > I would like to verify the postulate of 5 kV/cm required > to elongate up to, say, 1.5 m and 1 kV/cm required to elongate > further. These average field strengths look reasonable. It shouldn't be too hard to verify them. You could take a topvolts measurement and then use a closed formula for the field around a sphere or toroid - ignoring the coil altogether. I think Antonio and Godfrey were passing a few suitable formulas back and forth a while back, or were they just for surface fields? I should think you could just pretend the topload is a sphere as far as the average E-field gradient is concerned - once you get a little way from the topload it doesn't matter much what shape it is. It would be interesting to see how your 5kV/cm to 1kV/cm varies with risetime, bps, etc. But I think you will need to measure topvolts at some point. -- Paul Nicholson --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.