[esa-t474] spectrometer uncertainty

[Bino Maiheu]

Hi Eric,

>     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.

Indeed. I'm looking to some formulas to calculate the energy loss at the
moment, so I'll be producing some plots for reference. 

>     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.

Right, I don't think anyone is looking into this, but I'll definitely
put it on the list. Can do it quite easily with the simulation program. 


Thanks for your comments !

Cheers,
    bino

> 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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-- 
                                                  !!!!!
                                                 ( 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  /
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