From: Paul
Date: Fri, 11 Oct 2002 09:38:01 +0100
Subject: Re: [TSSP] Top Voltage
Bert wrote: > Is the presence of the larger toroid "shielding" the sphere, reducing > the effective E-field at its surface? This might explain higher than > expected breakout voltage... Yes, but the calculations have taken account of that (I think!). Boris wrote: > First,I didn't know the position of Terry's small > sphere was so close to toroid top (hm,hm, seems Terry > changed something in arrangment while not informing us > ..) Terry gave the size and position of the sphere in a post a couple of days ago. Lower than the earlier tests because it didn't have the current probe beneath the supporting rod. > 190 kv (Emax~42 kv/cm) > looks like we start blowing away breakout mysteries pretty well. Well I suppose we're somewhere in the right ballpark. Given the low frequency, the DC value of 30kV/cm may be a better starting point than 26kV/cm. With this lower sphere, we are slightly better with our predictions, ie less than a factor of two out! Maybe the (unmodeled) effect of the current probe (its distortion of the field) makes the difference, by lowering the surface field strength of the sphere. Referring to http://www.abelian.demon.co.uk/tssp/cmod/ we see John Freau's two setups just breaking out at a surface field of 42kV/cm and 35kV/cm, so same ballpark as Terry just measured. Marc gets multiple streamers when his coil tries to set the surface field to 53kV/cm. No breakout from Malcolm's at 13kV/cm, and Bart's is breaking out with short streamers at 26kV/cm. Between them, they all seem to bracket a range of values, which I would like to try to refine with base current measurements where possible. I guess we should keep on collecting breakout data for a variety of situations, just to get a good picture of the terrain. We're bound to see a spread, and we might be able to discern a correlation with Fres and k. -- Paul Nicholson, --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.