[esa-t474] All corrections to T474 paper complete

[Mark Slater]

Thanks for the comments, Yury. I have ammended the reply to points 2 and 
11 and changed the specs. I would be very grateful if this was checked to 
make sure I'm not talking rubbish! 

Chris A.: Has there been a direct measurement of the coupling for BPMs
3-5?

Yury: What are the specs for the front-end filter (the one centred at 
2856)?

Thanks,

Mark




> > ********************************
> > 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 damage to the cavity seems to have allowed the orthogonal mode to
be accepted by the coupler due to the change in geometry. In general, the
coupling in the rectangular cavities (1-2, 9-11) will be dominated by the
proximity to neighbouring cavities (around -30-40dB). There would be
direct coupling for the cylindrical cavities but this was measured to be
at a similar level. At the offsets recorded (~200um), it is highly
unlikely we would see a coupled signal in the orthogonal channel. During
calibrations (mover or corrector) when the offset was larger, any residual
seen is almost certainly going to be dominated by relative rotation errors
between the axes of the beam/BPM movement and the couplers making it 
difficult to measure from the beam data.

When you mention the artifact for BPM 4x, if you mean what is shown in Fig
22a, then this seems to be most likely due to non-linearities rather than
coupling as, assuming the y position was not correlated with x, then we
would expect a general worsening of resolution in x rather than a
correlation of the x residual with x position. Additionally, this
behaviour is seen in several other BPMs, both x and y.


> ********************************
>
> 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. Though
signal levels were measured we didn't think it necessary to include them
as the attenuation was varied per channel during the optimisation process
and the experimental data agreed with that predicted from
theory/specifications. This data also showed that the noise was dominated
by the digitisers.