[esa-t474] comments on paper draft 3, chapter 4
Bino Maiheu
bino at hep.ucl.ac.uk
Fri Sep 28 17:58:53 BST 2007
Hi Mark,
An other set of comments on chapter 4 from Alex and myself.
We weren't able to finish comments on the last two chapters by today,
but I'll go through it in detail tomorrow and send it before I leave.
Cheers,
bino
------------------------------------------------------------------------
General style remark for the figures
- I hate the word "tilt", suggest replace it everywhere by "slope"
which is much more commonly used in beam dynamics !!!!!!!!!!!!!!
- add ticks !! ->SetTicky(), ->SetTickx();
- ->SetLineWidth(1), otherwise when it gets NIM-ified, it'll look
rubbish
- precision -> resolution
accuracy : we cannot measure !
Comments to BPM commissioning paper Draft 3
-------------------------------------------
Chapter 3 : Kill it entirely & recycle it throughout the rest of the
paper !!!
3.1 -> moves to 4
3.2 -> dissolved in the text where systematic effects are
analysed !!
Chapter 4 : Commissioning the BPMs
-> kill 364->370 entirely, and replace by a much condensed version of
section 3.1 which just has the *relevant* equations in there !
-> So beginning of chapter 4 with old 3.1 :
- when showing equation 8, we should make it clear that this
formula allows us to distinguish between the offset and the
angular
component of the output voltage, provided we have a phase
reference.
-> Chapter 4 sectioning : suggest to change to :
4.1 Cavity frequency
4.2 Calibration
4.2.1 Corrector calibration
4.2.2 Mover calibration
4.3 System optimisation
4.3.1 Sampling point
4.3.2 Digital Filter Bandwidth
4.3.3 Attenuation and Alignment
4.3.4 Linearity of the BPM response
- line 372 : get rid of "(V(t) in Eq.10)"
- line 373 "...when downmixing to baseband (see Section 3.2.2"
suggest replace by : "... of the DDC signal."
- line 375 : need citation for MINUIT
- line 376 : "To avoid low amplitude effects." : not clear to reader
what is understood by this.
-> suggest replace by something like : "The fitting is most
efficient for large amplitude signals, so
this fit was..."
- line 377 : (~ 1 mm) ... make the cuts clear here !
- line 378 - 384 + table 5 and figure 10 : need rewriting/rethinking !
The way it is presented now is that one takes a period of 20
hours ( is this acutally 20 hours, because from figure 10 ( the
x-axis you can't tell ) ?) and fit for all the frequencies, put
them in one big histogram and fit for mean and stddev. If the
frequencies over this period are indeed distributed as a normal
distribution, then fine, but then we can't show the drifts
during this same period as this would mean that we fit something
with a gaussian which is not gaussian at all.
Suggest: we can present the data in table 5 from the first
point, in figure 10, were we say that we assume the long term
drifts to be small enough for us to assume that the obtained
frequencies are normally distributed, but not take the average
from the whole period !!
In figure 10 we can then show what these drifts look like, but
we definitely need some sort of uncertainty on these values
because the way these figures are presented now, they show clear
systematic drifts!
- line 385 - 392 : do we need this ?
- line 395 : as we got rid of section 3.2, we can put here section
3.2.3 instead of the brackets
- line 396 : Differences of ~ 0.5 MHz were achieved for all by BPM1y
( 39.90 MHz vs 36.70 --> see table Table 5 )
- figure 10 : in general - check Y axis labels
- time axis : proper labelling
- error bars needed !!
correlation plot with temperture ?
- table 5 : get rid of the "as q1" etc... just quote the values or
use double quotes
- table 5 : use the same precision ( number of significant digits )
for the quoted numbers and their errors !!!
- line 407 : probably best to have a correlation plot with
temperature here to support the statements or at least
give some
indication of the temperature variation over the period
considered.
- line 412 : The killed section 3.2.2. should go here then...
- Table 6 : Is very informative, we need something more in the sense
of "If my frequency changes by this amount, then the
resolution
and accuracy changes by that percentage...".
caption : "for each BPM if the physical frequency
changed by the amount given in Table 5" ?
What do you mean exactly, did you simulate BPM responses
with a slightly offset frequency ? -> Need explanation!
But if simulated, then what is the difference between
the different BPMs when simulated ? Or did you change
the DDC frequency and not the physical frequency ?
-> line 413 -> 424 prob. needs a bit of rethinking in the wake
of this comment
- line 417 : Section ??
- line 425 - 429 : This frequency change is not shown anywhere,
might be a bit confusing, or we have to put in a
plot showing it !
- line 431 : $(\omega)$ -> $\omega$
- line 433 : get rid of ($\Phi_{IQ}$ in Eq. 22) and similar
references !
- line 433 : scaling factor -> calibration or position scale
- line 437 : kill sentence "This movement not only..."
suggest replace : "...was applied, this way the rotation of the
position axis and the scale could be determined."
- Figure 11 : -> see general figure comments at top
-> bottom left plot : I suppose this is "uncalibrated
position" and not "measured", so should be in
arbitray units, not mm.
-> in the I vs Q plot, and the I,Q vs event number,
show that there was a slight drift between step 3
and 4, in I/Q : not equidistant fit point...
---> maybe use better calibration to demonstrate
to show principle
-> rephrase caption
- line 441 : kill first three sentences !
suggest change :
"By varying the magnetic field of correctors XCOR32 and YCOR33
in steps of 0.005 kG.m around the nominal value, we
scanned the position of the beam in all the BPMs. As
the change of the integral field of the magnets is known along
with the location of the BPMs in the beam line, a simple
calculation yields the predicted offset in each BPM at each
step."
- line 446 : "For each of these events..."
suggest change : "For each of the steps, the I and Q values
of the events were computed and fitted to a Gaussian to
determine..."
- line 447 "gaussian" -> "Gaussian"
- line 448 : beam jitter is not really in place here, get rid of it!
- line 448-452 : "The values at these set points...." needs a bit
rewriting + some extra explanation
suggest : "As the orbit correctors are far enough from the
BPM stations, the induced slope is negligeable
compared to the position offset, so that points
(I,Q) for each step have to form a straight
line. The $\Phi_{IQ}$ is then given by the slope
of that line in the IQ plane. Applying a
coordinate rotation of $\Phi_{IQ}$ to the IQ
plane ( see eq...) yields the uncalibrated
position. The calibration scale is subsequently
determined from a straight line fit .... bla bla
bla...."
- line 458 : "A significant drawback..." .. true, but one could use
BPM 31/32 ... maybe comment on that !
- line 464 : "In addition to these problem..." until the end of the
paragraph
suggest rewrite : "In addition, there was no instrumentation
available to monitor the actual magnetic fields in the
correctors." full stop.
- line 470 : Section 2.6 -> "section 2.6", but will probl be
different number ! check it
- Figure 12: Too large,
Caption "relationship between the beam and a
triplet"... don't really think they are in love ;)
-> in fact, kill the entire figure, not very informative
- line 471 - 474 : suggest replace by :
"The beam jitter could be removed using the readings from
the two outer BPMs in the triplet for the events in which
the central BPM has moved. This results in a significantly
more accurate method of calibration. Furthermore the
horizontal
position of these 3 BPMs was monitored by an
interferometer, improving the calibration in x."
- line 475 : "the Zygo interferometer" replace everywhere by simply
"the interferometer", Zygo is a brand and is
irrelevant and jargon.
- line 476 : remove last sentence, accuracy already mentioned before
- Eq 28 : Get rid of the k, and replace by 4. In ESA we only have 1
BPM on a mover, so no need to have an index "k". Also
replace the indices of the sum to "\sum_{i=3,5}"
- Eq 29, see remark above and also the vector with the correleation
coefficients should be a small letter, not capital "K" to
indicate that it is a *vector* of values, not a matrix.
- line 503 : get rid of the brackets around the (I), (Q) and (x)
- line 505 : refer to eq 29 instead of 31.
- line 505 : "First, the..." replace by "First, the position and
slope readings of the outer BPMs"
- Figure 13 : - left bottom shows no label
- ticks, line thickness all 1 !
- "Run 1374 has been used" ( run 1374 )
- top plots x axis need different division scale (
SetNDivision(...) or something in ROOT )
- line 517 : -1 to +1 mm doesn't correspond with the predicted
position in the bottom right graph of figure 13
- line 517 : "...(the actual values....)". get rid of this, already
mentioned
- line 519 : "..were determined from the central BPM step"
suggest replace by "...was determined from the middle step"
and get rid of "(at zero relative offset)".
- line 523 : typo "detemining".. missing r
- line 527 -> 530 : needs rephrasing + discussion on what was done
here !!
- 4.3.3 : System optimisation : need some intro on alignment and
attenuation bla bla as well, so add :
"Also the gain of the electonics had to adjusted to fit the
required range of the beam offset to the range of the
digitisers. A beam based alignment techique has been applied
to match the dynamic range of all the BPMs."
- Table 7 :
- sample point in MHz ??
- gaussian -> "Gaussian"
- caption "... to centre the gaussian filter." Hmm, sounds
funny to center a filter around a point in time domain.
- what do we learn from this table ? Not much we think, need
some kind of reference, or say how far down the waveform
from the maximum we are, so correlate with decay time.
- Ah, but wait!! In the text it's mentioned that the sampling
point is 10% down from the maximum, so don't think this table
makes
much sense.
- Also, when we pick the point to be at 10%, it is not really
optimising...
---> need some discussion !!!
- line 544 : "... and the phase was stable." : this needs some
explanation as this is not trivial. Need to refer to
figure 9.
- line 552 : "nagligible" : typo
- Table 8 : we have to explain why the optimum values for the filter
bandwiths are different. So what we're seeing is the
effect of the short decay times for BPM3-5, resulting in
a much more broadband response in frequency
domain. Therefore, the filter needs to be more broadband
as well in order not to cut in the signal and loose
sensitivity.
-> or something phrased a bit more decently in that sense !
- Table 9 : the errors in the table are meaningless, get rid of
them.
- line 563 : "... was measured." -> "... was measured with a
precision of a few micron."
- section 4.4 : Need to mention somewhere :
"Most of the BPMs were aligned to better than $\pm$
150 $\mu$m.
- line 572 : what is "good ?" need to quantify "linearity".
-> need a good definition of linearity !!1
"The range in mm in which the BPM amplitude does not
deviate from a straight line by more than some %"
-> ideally even 0.05 % ( 500 nm resolution on dynamic range
of 1 mm )
-> need to discuss !!!!!!
-------------------------------------------
--
!!!!!
( o o )
@ -- Bino Maiheu, Dr. ;) ---------oOO----(_)----OOo------- @
/ :: WORK .:: / :: HOME .:: /
/ University College London / /
/ Physics and Astronomy / 31 Kilgour Road /
/ Gower Street / Forest Hill /
/ London WC1E 6BT / London SE23 1PG /
/ [tel] +44 20 7679 3454 / United Kingdom /
/ [fax] +44 20 7679 7145 / [mob] +44 7747 75 58 78 /
@ -------------------------------------------------------- @
More information about the esa-t474
mailing list