[esa-t474] BPM frequencies

[Mark Slater]

Hi Alex,

	The modes are certainly rotated with respect to the couplers, but
what I've found is that moving the BPM in the XY plane affects the Tilt
(quadrature) value of the response, not just the position (in-phase) part
(hence the fact that you can see the 2d scan when plotting I vs. Q). I
would have expected that, even with the modes rotated, you should still
have a definite position and tilt axis to fit an IQ phase to.  If so, then
I'm currently not sure whether this is due to DDC issues or maybe the Q
cavity.

Thanks,

Mark

On Thu, 7 Feb 2008, Alexey Lyapin wrote:

> 
> Hi Mark,
> 
> It sounds like the two polarisations of the dipole mode in BPM7 are rotated
> with respect to the couplers. That means that even selecting one polarisation
> you do not isolate x or y signals. I think what we need to learn from the 2D
> scan is the rotation angle of the polarisations axes vs x and y. Plotting the
> power density or the amplitude from a frequency-constrained fit obtained at
> the frequency of one of the modes vs x and y (3D or intensity plot?) may be
> informative.
> 
> Cheers,
> Alex
> 
> 
> Mark Slater wrote:
> > Just as a bit of an aside on the split frequencies of x7 and y7, I've had a
> > brief look at these myself:
> > 
> > http://pcfj.hep.phy.cam.ac.uk:8080/slater/
> > 
> > entries 42 and 43. I'm going to try to make more headway here so we can
> > actually get meaningful positions out of the BPM.
> > 
> > Thanks,
> > 
> > Mark
> > 
> > 
> > On Wed, 6 Feb 2008, Bino Maiheu wrote:
> > 
> > >    Dear All,
> > > 
> > > As a first step in the analysis of the July 07 data, I've started by
> > > having a real close look to the frequencies of the waveforms as they are
> > > needed for the calibration of the BPMs and I want to understand any
> > > systematics as good as possible.
> > > 
> > > I've fitted every BPM waveform with a decaying exponential, using a
> > > constrained fit with the frequency and width of the fourier transform
> > > peak as initial input. This fit, although somewhat slow, seems to be
> > > working fine. The FFT spectra, frequencies etc are available from
> > > 
> > > http://www.hep.ucl.ac.uk/lc/T474/EsaData/fits.0/
> > > 
> > > where the fit parameters of each fit are stored in the root files as
> > > well. I'll upload macros into cvs later on to plot the fit functions on
> > > top of the waveform and FT. So far, I've plotted these frequencies versus
> > > pulse number and updated
> > > the data quality web-database with the plots. So far runs 2725->2850 are
> > > there, with the others on the way (takes about 50-60 hours for a single
> > > average run). I've made a cut on the chi2/ndf for plotting the
> > > frequencies, showing only 'decent' quality fitted frequencies. As Yury and
> > > Zen figured out, we were running on internal clock, so I
> > > have taken this into account, the IF frequency values shown are in MHz
> > > ( note the fact that we were undersampling for all but BPM7 ).
> > > 
> > > http://www.hep.ucl.ac.uk/lc/T474/EsaRunInfo/show_dq.php
> > > 
> > > ( currently 2735 -> 2850 )
> > > 
> > > I'll make a plot of the average frequency per run with the error, but i
> > > will need to look a bit in detail since some of the distributions are
> > > not nicely Gaussian, so that I pick the correct frequency for accurate
> > > calibration of the DDC algorithm. One thing i noticed, see e.g.:
> > > 
> > > http://www.hep.ucl.ac.uk/lc/T474/EsaRunInfo/show_dq.php?run=2725&plot=7
> > > 
> > > is that the frequency for BPM 12/24 waveforms seems quite unstable, I
> > > suspect this to be due to changes in the LO for these channels. Also,
> > > once can clearly see a double frequency structure for BPM 7. Anyway, as I
> > > said, I'll determing the averages to use as input for the
> > > DDC from this as Mark learned that this gives the best resolution. I'll
> > > add the plots for the decay constants and t0 from the fits as well. I'll
> > > keep you informed of my progress.
> > > 
> > > Bino
> > > 
> > > -- 
> > >                                                   !!!!!
> > >                                                  ( o o )
> > >           @ -- Bino Maiheu, Dr. ;) ---------oOO----(_)----OOo------- @
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> > >         /  University College London   /                           /
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> > >   @ -------------------------------------------------------- @
> > > 
> > > 
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