T-474 phone conference
Thursday 22 june 2006, 16:00 GMT+1 (08:00 PDT, 11:00 EDT)Phone number : (+ 1) 510-665-5437
Meeting code : 4194
Minutes of the 22 June 2006 T474 Phone conference ------------------------------------------------- - The funky IQ plots on the q10 reference cavity are due to the fact that the cables were swapped inbetween the q and x cavity for the last couple of runs. - Apart from a couple of lonely runs, the external clock runs are basically reprocessed. They reside currently at UCL but will be copied to the same datadisk at SLAC. Will communicate by email on this. - Main discussion point is the phase dependence of the resolution, for which Mark seems to have found a clear hint from his MC simulation, where he varies the phase of the generated waveform keeping the amplitude constant. This seems to generate a small but large enough phase dependence of the DDC amplitude. Yury thinks this might be due to some non perfect filtering of the double-frequency component of the downconversion. So a couple of questions arose : o Does the amplitude of the residual sin-wave scale with the filter bandwidth ? -> clear hint ! o Can we get rid of this effect by some IQ rotation ? o Can this behaviour be fixed by tuning the frequency or the t0Ref ? o Would reducing the filter bandwidth help ? Or cut-off parameter ? o Behaviour same for real and imaginary part ? Further checks in MC : o check effect of going off-frequency o can we predict the phase of this residual harmonic, either by MC simulation of by rigorously going through the math, and possibly correct for it in the algorithm ? Eventually, w.c.s. we could try out different filters as well, if this proves to be the problem. - Now that the reprocessing of the external clock runs is basically done, it's time to revisit the systematics! Mark will have a think again and put something in the eLog for everybody to add/comment. o Need resolutions tabulated versus various beam conditions, optics o Should *really* revisit the extrapolation in DDC possibly enabling us to move t0 back in the waveform, enhancing signal/noise. o Look at stability of frequencies, gamma's etc... o Relationships between BPM stations, orbit fitting - The berkeley gang will come up with some macros for all of this. Yury will take the libRooEsa library from the UCL CVS and put it into the main CVS at SLAC together with the rest of the data production code. - We will try to have a phone conference next week, will communicate to esa-t474 list.