From: Paul
Date: Mon, 16 Jul 2001 11:08:03 +0100
Subject: Re: [TSSP] Thor base current measured
Marco, Over the weekend I did some more work on comparing your base current with the model. Unfortunately, the results on closer inspection are rather poor. The problem is due to poor accuracy of the model's prediction of the higher mode frequencies. You may recall that I've been trying to improve the Cint interpolation, I now have four different routines, all of which generate slightly different answers, some of which are almost 5% out and therefore quite useless. So far, the only encouraging thing is that if I cheat and manually set the mode frequencies to match an FT of your waveform, the resulting phase and amplitude match is very good indeed, which suggests that the modal decomposition stuff (pn1401 section 7) is working OK. A similar problem prevents successful comparison of Terry's high-k measurements too. I think I'm going to have to put these base current readings to one side for the time being, until the Cint interpolation and material dielectric corrections are working properly. On a more positive note, I think we can safely conclude from yours and Terry's measurements, that the secondary is being excited significantly (mode 3 amplitude between 1% and 10% of mode 1 and 2) at higher modes, and that the proportion increases with k. See http://www.abelian.demon.co.uk/tssp/md110701/md110701-g.gif which compares predicted and modeled spectra. Note the size of the mode 3 current. The problem now is whether this higher mode excitation is the limiting factor when raising k. Apologies to anyone waiting for the latest revision of code - promised a few weeks ago! I'm a bit stuck at the moment with this Cint thing. BTW, the initial ringing contains frequency components at 1.92Mhz, 2.09 Mhz, 5.68Mhz, 7.26Mhz, all +/- 50kHz. Don't know where I got the 800kHz from that I mentioned in an earlier message! Cheers, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.