From: Paul
Date: Tue, 08 Oct 2002 08:52:26 +0100
Subject: Re: [TSSP] Top Voltage
Marc wrote: > The space charge is a very strong field i think. Terry wrote: > I am thinking the toroid is breaking out all over and > "poisoning" the space around the small top ball with flying > ions. If space charge is having an effect, we should be able to detect it by noticing a change to the effective C of the topload, and this would occur before the visible breakout. Terry, I'm hoping you can measure the average rod+sphere probe current and the average sec base current, for various power levels leading up the observed breakout. Plotting probe current against base current way show a tell-tale deviation from the straight line as the power goes up. We can also try to detect a rectification of top terminal current. A cap of 0.1uF in the base would have around 40 ohms reactance, so at most a 50-100 or so RF volts across it. If breakout occured, the DC charge that accumulates on this cap would be equal to the total net rectified charge put out by the topload. At most, if the entire firing energy was rectified and stored in the 0.1uF cap, you would have Vfire * sqrt(47uF/0.1uF) DC volts on the cap, so you could end up with a few kV. That's just one bang. If you allowed charge to accumulate over more bangs, the voltage could continue to rise. Can I suggest around 0.1uF with a 2.5kV Victoreen gap across it to dump any excess DC? -- Paul Nicholson, --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.