[Tpe] TPE beam monitors

[Will Brooks]

Dear Larry,

 The other position we discussed for the calorimeter was downstream of 
CLAS. That would allow much more flexibility in repeated changes, but it 
should be checked whether the free aperture is enough for the collimated 
beams to be transported that far without hitting anything.

Thanks,

 - Will



Larry Weinstein wrote:
> Dear TPE-ers,
>
> We have several beam monitors available for TPE:
>
>    1. two quartz crystal background monitors located in the chicane
>       just before the PS magnet.  They will give real time monitoring
>       of shifts in the relative intensity of the left and right beams.
>    2. fiber monitor plus calorimeter.  The FM will be directly in
>       front of the calorimeter to provide much improved position
>       resolution.  The combination will be placed in the beam during
>       chicane tuning to measure the energy vs position spreads of the
>       e+ and e- beams separately.  (We will block the individual beams
>       to measure the other beam by itself.)  This will be done once or
>       twice during the measurement.  There are two possible locations
>       for the detector:
>          1. upstream of the steel shield (as shown on the current
>             drawings).  This might not give enough lever arm to
>             measure the beams.
>          2. at the target (as advocated by certain people).  This
>             would give a much better measure of the beam position vs
>             energy at the target, but would have a huge overhead (2
>             days?) for insertion and removal.
>    3. reaction vertex measurement by CLAS.  This will not be a real
>       time measurement, but I hope we can organize near-online data
>       analysis to give us this information a few hours later.
>    4. a possible sparse-fiber monitor (1 mm fibers every 5 mm) located
>       at the downstream collimator (where it was during the test run)
>
> Open questions:
>
>    1. where should we locate the calorimeter?
>    2. do we need the sparse-fiber monitor?
>
> 1. We are simulating the beam profile at the two possible locations.  
> We will also discuss this with Dave Kashy to see if it is even 
> possible to place it at the target.
> 2. I am not sure what we will learn from the sparse-fiber monitor.  It 
> will give us relatively poor beam centroid information and very poor 
> beam width information.  If the italian dipole fields drift, then the 
> beam centroid will not change, but the width will increase slightly.  
> I am not sure what could change that would give a significant change 
> in the sparse fiber monitor.  At present, I am inclined to leave it out.
>
>
> -- 
> 				Sincerely,
> 				Larry 
>
> -----------------------------------------------------------
> Lawrence Weinstein
> University Professor 
> Physics Department
> Old Dominion University
> Norfolk, VA 23529
> 757 683 5803
> 757 683 5809 (fax)
> weinstein at odu.edu <mailto:weinstein at odu.edu>
> http://www.physics.odu.edu/~weinstei <http://www.physics.odu.edu/%7Eweinstei>
>   
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