[esa-t474] All corrections to T474 paper complete

[Mark Slater]

Dear All,

After help from Alex, I believe I've now answered (and corrected) all the 
points raised by the reviewer. As before, the new version is 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

I plan to submit in TWO WEEKS TIME!! If anyone has any 
comments/criticisms/complaints, please let me know before then!

Thanks,

Mark

P.S. Comments that I will send to the reviewer are listed below:


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:

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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.


MWS:  Reworded these paragraphs

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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).

MWS:  The artifact seen in 4x (assuming you mean fig. 22a) is just an
example seen in other BPMs - notably y and 9-11. If it was leaking from 
the y direction, I would expect it to show an overall worsening of 
resolution, not a correlation (unless the y movement of the beam was 
correlated with the x movement, which it didn't seem to be).

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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.

MWS:  Removed most of the ESA references in the A-line section and added 
another 
sub-heading

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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?

MWS:  changed to Ref. Cavities

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5) Fig 16 is missing the plot legends.


MWS:  Fixed

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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.

MWS:  All plot labels fixed

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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?

MWS:  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.

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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.

MWS:  Done

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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?

MWS:  I have reworded the statement on attenuation optimisation to 
indicate that this is what we do, i.e. we optimise the signal levels so 
that we get the best range (~+-1mm) and the best resolution (largest 
gain).

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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.

MWS:  Added to captions

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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.

MWS:  Added more specifications on the equipment, added the BPM 
sensitivity and improved the discussion on dominant noise sources. 
Unfortunately, we don't have the data available for the signal levels 
through the electronics chain, but a quick analysis showed that the 
thermal noise level was significantly below the digitiser noise level and 
so this was assumed to be domoinant.

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12) Minor grammatical errors on lines 587, 654, and 656.

MWS:  Fixed

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