[esa-t474] New version of paper available

[Alexey Lyapin]

Hi Mark,

I guess the issue in BPM1 is not just detuning, but the modes are not 
entirely orthogonal - the initial polarizations split into submodes as 
the result of the damage, which can be sensitive to both x and y and 
strongly coupled (can only speculate about that). The reviewer may or 
may not be right about the filter, I don't really know how far apart the 
two polarizations were initially supposed to be.
I beleive the artifact in BPM4x is the feature seen in our small signal 
plots, where the residual depends on the position. Probably what he says 
is that we could make a similar plot for BPM1 and learn something from it.

We can quote the sensitivity as something close to 1 V/mm/nC at the peak 
(though it's different for individual BPMs). Not sure about typical 
signal levels as we are working in a wide range of the offsets. We could 
draw a level diagram similar to the one you made for nanoBPM some time 
ago, but I think this is a step back to discussing noise/resolution, 
while we are addressing stability. Besides, discussing electronics noise 
is worth nothing as we are getting resolutions close to the ADC bit 
resolution - maybe that should be mentioned. Components specs can be put 
in, but I doubt we have any temp stability data, which would be the 
interesting bit.


Cheers,
Alex


Mark Slater wrote:
> Dear All
> 
> 	I have added almost all the corrections indicated by the reviewer.  
> Below is a list of the alterations. The only points I have issue with are
> (2) where he talks about an artifact for BPM 4x which I didn't realise we
> had and point (11) for which I'm going to need someone else to write up,
> or at least send me the info so I can write it up.
> 
> If people can help with either of these, do let me know ASAP!
> 
> However, as I say, the majority were not a problem and I've implemented 
> them. You can see find the new version at:
> 
> www.hep.phy.cam.ac.uk/~slater/esabpm.pdf
> www.hep.phy.cam.ac.uk/~slater/esabpm.ps
> 
> the submitted version can be fonud at:
> 
> www.hep.phy.cam.ac.uk/~slater/esabpm_old.pdf
> www.hep.phy.cam.ac.uk/~slater/esabpm_old.ps
> 
> !!NOTE CHANGE OF WEB ADDRESS!!
> 
> Thanks,
> 
> Mark
> 
> 
> 
> 
> 
> Reviewer #1: I believe this is a valuable, relevant to NIM, and very 
> detailed manuscript. The community will benefit 
> 
> from its publication. I have the
> following comments, all of which should be solvable by simple editing:
> 
> ********************************
> 1) The discussion starting with line 441 and ending with line 474 is 
> confusing. I will attempt to summarize my 
> 
> understanding of it: On each shot, eight
> pieces of data are collected from the outer two BPM's, including the I and 
> Q signals in each direction. The 
> 
> correlations between this data and the the I and
> Q of the central BPM are analyzed over many shots, such that eighteen 
> linear parameters are found that best predict 
> 
> the central BPM data (nine parameters for
> I, and nine parameters for Q).
> 
> If that is the case, then the authors should explicitly state that x_i and 
> x'_i in Equation 16 are derived from the I 
> 
> and Q signals of one of the outer
> BPM's. The phrase "outer BPM coordinates" sounds vague, since coordinates 
> could be taken to mean positions only.
> 
> Reworded these paragraphs
> 
> ********************************
> 2) In several places (line 178 on p. 12, and later, in lines 671 to 674 on 
> p. 42, line 587, p. 35), the paper talks 
> 
> about unwanted coupling with other modes
> in the cavity. BPM 1 is said to have rectangular cavities, and I am 
> guessing that the mechanical damage brought the 
> 
> detuned orthogonal mode closer to the
> filter acceptance window.  Is the artifact in the BPM 4x signal due to the 
> same issue? In that case, analysis of the 
> 
> residual vs. motion in the y-direction
> would give a much clearer indication of the source of the cross-coupling 
> (if data is available).
> 
> 
> Is he correct in saying that the detuned orthoganal mode was closer to the 
> acceptance window of the filter?
> There is no artifact in the 4x signal! 
> 
> ********************************
> 
> 3) I recommend the description of the SLAC "A-line" (line 82 on p. 6 to 
> line 121 on p. 8) to be better "decoupled" 
> 
> from the discussion of the ESA beamline.
> Initially, I was looking for BPM's 1-9 in the Figure 3 description of the 
> A-line, and only realized the general 
> 
> layout of the beamline components after
> re-reading both sections a couple of times.
> 
> Removed most of the ESA references in the A-line section and added another 
> sub-heading
> 
> ********************************
> 
> 4) Table 7: the fourth entry in the table is "Q cavities". I could not 
> find in the text what this refers to. Are 
> 
> these the phase reference cavities?
> 
> changed to Ref. Cavities
> 
> ********************************
> 
> 5) Fig 16 is missing the plot legends.
> 
> 
> Fixed
> 
> ********************************
> 
> 6) In some of the plots, a label such as "BPM 4x Residual" is easy to 
> mistakenly read it as "four times"  the 
> 
> residual, thus giving the impression that the
> signal was rescaled by a factor of four. A notation such as BPM-4X might 
> make it easier to interpret the plots.
> 
> All plot labels fixed
> 
> ********************************
> 
> 7) The definition of "linked" system resolution starting in line 544, p. 
> 32 is a bit vague. Assuming a straight line 
> 
> trajectory through a set of BPM's, the
> residual of each BPM is calculated, which gives up to eight numbers. At 
> this point, I am confused about whether a 
> 
> single BPM is selected and the RMS value of
> its residual is called the "linked" system resolution, or whether a 
> further RMS is performed on all the residuals of 
> 
> up to eight BPM's in the set. In the
> case of a single BPM, how is that BPM selected?
> 
> This is incorrect. The residual of a single BPM is calculated from a 
> prediction formed from all but the neighbouring 
> 
> BPMs. Reworded this to make it clearer.
> 
> ********************************
> 
> 8) Table 8 and its discussion would be clearer if: 1) the table column 
> headings were called something like "Measured 
> 
> resolution, x", and "Predicted
> resolution, x", etc. and; 2) The sentence on line 552, p. 33 was changed 
> to alert the reader that predicted 
> 
> resolution is defined in the next paragraph.
> 
> Done
> 
> ********************************
> 
> 9) In the discussion of measured system resolution on line 554, p. 33, I 
> wonder if the digitizer was operated near 
> 
> the peak of its range, or would additional
> signal amplification further reduce the digitizer noise?
> 
> I have reworded the statement on attenuation optimisation to indicate that 
> this is what we do
> 
> ********************************
> 
> 10) Figure 18, I can guess that the black points are the mean, and the red 
> region is the RMS width, but it should be 
> 
> stated explicitly. Also, the meaning of
> the green lines is not at all apparent.
> 
> Added to captions
> 
> ********************************
> 
> 11) In general, the paper would benefit from a statement of the BPM 
> sensitivity (signal voltage for a given bunch 
> 
> charge and displacement),  typical signal
> levels seen at various points in the processing electronics, a more 
> detailed description of the electronics 
> 
> components used (mixers, amplifier), and a
> discussion of the likely sources of electronic noise.
> 
> ********************************
> 
> 12) Minor grammatical errors on lines 587, 654, and 656.
> 
> Fixed
> 
> ********************************
> 
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