From: Paul
Date: Sat, 11 May 2002 23:25:27 +0100
Subject: Re: [TSSP] Topload breakout potentials
Marc wrote: > Topload toroid is a fairly smooth 6.5" aluminum ducting with > a total diameter of 30.5" so 6.5" x 30.5" > I tried measuring capacitance of it but i came up with 29.6pf, > wintesla says 33.01pf for it? Floating in free space, this toroid would have 32.462574 pF. Inside your room (with my guesses for walls, ceiling, etc) it comes out around 42.3pF, and in-situ above the coil it contributes 36.2pF to the total shunt capacitance of the resonator. The toploaded secondary Fres comes out around 38.5 kHz, I assumed the toroid is mounted just clear of the top of the coil. The primary seems to be tuned a little lower - 36 kHz, so either the model is over 6% out on frequency, or you are doing the same as John - tuning the primary to the low side of the secondary. With a secondary Cee of 44.7 pF, your primary bang energy of 0.5 * 52 nF * 34 kV^2 = 30J would give a peak topvolts of sqrt( 2 * 30J/44.7pF) = 1160 kV if tuned. This topload has a highest surface gradient of 0.031 V/cm per volt of topvolts. Therefore your toroid surface field will try to reach 0.031 * 1160 = 36 kV/cm, which ought to give very early breakout with lots of short streamers. Incidentally, if tuned correctly, the average gradient along the secondary would be 1160kV/103cm = 11.3 kV/cm, and the stress factor for your h/d=4.6 winding is around 1.37, so giving a maximum gradient of 11.3 * 1.37 = 15.6 kV/cm, not including any 'corrugation' factor. The computer is currently working on the out of tune model using your tap settings and it should be done in a couple of hours, so it will be interesting to see what surface gradient that reaches. How can we determine whether Marc's and John's primaries are really tuned low, or whether the model is just not representing them properly? Tuning low seems to keep quite a lot of energy in the primary, thus reducing the peak topvolts but perhaps enabling the beat envelope to be sustained over more beats, thus generating fewer streamers but allowing them to grow longer. Is this a recommended way to deal with a too-small topload? -- Paul Nicholson, --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.