[esa-t474] spectrometer uncertainty

[Eric Torrence]

Hi Bino,

    This stuff is important, and I am glad somebody is
trying to think about it deeply.  You should state right
up front in your note that you are defining E_beam as
the beam energy in the middle of the chicane.  I don't
know how much energy loss there is in the ESA chicane
(something you should calculate) but I would guess the
beam energy loss through each dipole pair is significant
at the 100 ppm level.

    Also, don't forget about the installed precision on
the roll of the magnets.  This directly affects int(B dl)
and probably will be one of your largest uncertainties.
It is possible that you can actually measure this better
than the survey accuracy from the BPM data by looking for
a "bend" in the vertical direction, although you will be
fighting against a sin(theta) term.  Perhaps this is
already being done.

Regards,
-Eric

On Dec 5, 2007, at 8:10 AM, Bino Maiheu wrote:

> 	Dear All,
>
> I've started some studies concerning the uncertainty and the overall
> layout of the chicane. I wanted to make some plots first of all in the
> style of Karl-Heinz Hiller ( see LC-DET-2004-031 ), but for a 4 magnet
> chicane. I think it's important that we have a think about how to
> calculate the energy in a 4 magnet chicane and that we fix the  
> formalism
> for later studies. So I've started a small writeup, which you can  
> see in
> attachment.
>
> I also included a plots which shows the \Delta E/E versus \Delta B/B,
> distance between the first 2 magnets, distance between the central BPM
> and the second magnet ( as these are the 2 independent  
> variables ! ) and
> the uncertainty on these quantities, for BPM resolutions of 1um, 500,
> 100 and 50 nm. There is more explanation in what I have written so  
> far,
> which are nothing more than some initial thoughts, but I wanted to
> distribute this already now for early feedback.
>
> My plan next is to extrapolate these plots for ILC chicane and
> subsequently use a full Geant 4 simulation with real fieldmaps to
> reproduce and study these curves more in detail as a function of
> magnetic field uniformity and misalignments of BPMs and Magnets.
>
> Questions and sort of drafting of a TODO list are welcome.
>
> Bino
>
>
> -- 
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