[esa-t474] BPM frequencies

[Alexey Lyapin]

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 )
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