[Tpe] TPE beam monitors

[Larry Weinstein]

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
http://www.physics.odu.edu/~weinstei

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