T-474 phone conference

Thursday 15 june 2006, 16:00 GMT+1

discussion points

• plots and analysis progress can be found as usual in the T474 analysis eLog
• bug/feature fix in code, status
• optimisation results for external clocking DDC
• start recalibrating/reprocessing external clock runs
• documentation of analysis code, optimisation and settings : started a note about it, which is in CVS on the web (together with start of collection of analysis code for BPMs in ESA)

minutes

  Minutes of the 15 June 2006 T474 Phone conference
  -------------------------------------------------

- Bino reported on the progress that was made in the BPM analysis and
  the DDC optimisation. The key was finding that the algorithm in the
  lastest version of the code had a bug. The IQ plots had a lot of
  phase jitter. The reason for this was incorrect treatment of the
  filtering algoritm in timedomain, where the filter reference time
  (tfilter) was put to the starttime (startFit, picked up from
  calibration file) and the end time, tstop, was put to that value
  +dt, where dt is calculated from the filter bandwidth. This 
  technically speaking reduces the bandwidth of the filter as well by
  a factor of 2.

  This issue is extensively supported by plots in the electronic
  logbooks at :

  https://www.hep.ucl.ac.uk/elog/Bino's+logBook/5
  https://www.hep.ucl.ac.uk/elog/Bino's+logBook/4
  https://www.hep.ucl.ac.uk/elog/T-474/16

  A new version of the code (NanoModules version yury-13jun06a) was
  sent around by Yury, with the following changes :
    * the value t0Ref picked up from the calibration files now refers
      to the filter time (tfilter)
    * tstart = tfilter - dt, tstop = tfilter + dt

  This code produced good IQ plots again so optimisation could
  continue. 

- For external clock data, the optimal bandwidth and t0 Bino and Yury
  agree upon to be 
  t0     = 68.0
  filtBW = 0.20
  For t0Ref Yury finds an optimal value of 86, which produces after
  some fudging resolutions on BPMs 3-5 of 500nm in y and about 800 nm
  in x, Bino finds 89 as optimal value with slightly worse resolutions
  in y at 800 nm and x ~ 1 um. 

  Having the tfilter value a little further (89) filters the waveform
  only at it's end, thus conveniently bypassing any saturation effects
  but having a slightly worse resolution. Having tfilter at 86 takes
  more of the beginning of the waveform into account, thus having
  better resolution, but more sensitive to saturation effects. So this
  is also the reason why Yury had to apply some 'fudging' to account
  for saturation effects that might slip into the calibration. 

  So basically this boils down to the fact that we need to find a way
  to treat saturation better in the DDC algorithm. 

- The idea there is to have a look to the downconverted waveform,
  try to fit the gamma's and use those then. However problem here is
  that for some strange reason the phase has a slope across the
  pulse. This slope can be changed by tweaking the frequency assuming
  that this dependence is linear with time. This is however not the
  case, so the phase slope changes with amplitude (eg. in calibration
  runs) 

  The reason for this is either maybe influence from a monopole
  component or some other pathology (possibly hardware related). Note
  that there appear also 2 peaks for e.g. 417-419 in the FFT spectra,
  which give possible indications for hardware problems...

  So the play here is to use a macro called "plotDDC.C" in NanoMacros
  (version yury-13jun06a) and tweak the frequencies manually in order
  to make the phase plots flat across the pulse, next step is to fit
  the gamma's in the downconverted waveforms and use those in the DDC
  algoritm.

  ---> In future we will tabulate this variation of the phase across
       the pulse and correct for it by means of a lookup table....

- Yury brought up the issue of runs 960, which have external clocking
  and where the terminators were removed. This effectively changes the
  frequency and the width of the cavity, so one should take care of
  that when optimizing the data. This will be taken care of.

- Chit produced a new set of waveform info files for the entire
  runrange having the correct settings depending on internal or
  external clocking. Yury will send these around as a tarball.
  Bino produced new values for the fixed t0 for external clock, he
  will send these around as well.

- Yury will commit a new version of the t0 finding routine for
  internal clocking, which essentially removes the code which 'goes
  back a couple of samples' to do the linear fit of the rising edge of
  the trigger pulse. This should hopefully improve t0 determination
  for internal clock runs and resolution.

- Bino brought up an issue about calibrations where the IQ phase is
  around pi/2. Yury suspects this is probably due to saturation and
  not so much the actuall IQphase value. A quick check by slightly
  changing t0 (which changes the IQ phase) should bring clarity on
  this issue.

- Bino was wondering why the phase difference between q9Phase and q10Phase
  is more or less Pi. This is purely by coincidence Yury informed
  :). It brought up however the issue of looking to the Phase
  resolution. Bino will put up a plot in the eLog so we have an idea
  about it.  

- The conversion of the calibration files to have the real frequencies
  and widths of the cavities (so to make them uniform between external
  and internal clocking) has been postponed as everyone seems to be
  happy with the current version. Might implement it once the entire
  optimisatio/understanding of the data is finished.

- Plans for future :

   o split calibration / reprocessing according to internal & external
     clocking...	       

   o Implement a correction table for the phase change with time in
     the DDC algoritm...

   o Check whether the ADC values for the corrector magnets are in the 
     root files and write some code to automatically have this do the 
     calibrations, possibly having calibrations 'on the fly'...

- A mailing list was setup called '[email protected]' for mass
  mail concerning T474 analysis. To subscribe, people should send an
  email to "[email protected]" with an empty subject and
  in the message body "subscribe address="
  

- Time for phone conference next week will be decided via email
  exchange as Yury is away.