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Re: Tagger design



Tim, Franz,

Another possibility would be to put the microscope BEHIND the fixed 
array.  The fixed array counters are only 4mm thick, and the entrance 
window to the microscope could be located a few cm behind those 
counters.  The geometry of the microscope works equally well in the two 
positions.  On the other hand, pushing back the fixed array makes its 
support rail substantially longer (several meters) at the downstream end 
(9GeV electrons, 3GeV photons).  It also makes sense at the low-energy 
end of the focal plane (photon energies near the end-point) to have the 
fixed array counters right next to the exit window.  There the focal 
plane deviates substantially from a straight line and having 70 cm of 
extra flight path between the focal plane and the tagging counters down 
there is not ideal.  If we put them next to the exit window there then 
we might as well design it that way along the entire focal plane.

In the present design, we are configuring the fixed array to be able to 
do endpoint tagging without the microscope, just using the fixed array.  
With the latest microscope design, there is now the added possibility of 
reconfiguring the microscope for endpoint running and moving it down 
there behind the fixed array in case one wants the highest tagging 
resolution and rates at the highest energies.  Given the low profile of 
the fixed array and the extended support that is needed to hold it, I 
think it makes the most sense to put it next to the exit window and 
mount the microscope behind it on a movable table.

Richard Jones

Tim Whitlatch wrote:
> Hi Richard,
>
> We can move it back as far as you wish (within reason). When all the 
> numbers and locations are agreed upon, we will update the drawings to 
> reflect the changes.
>
> Cheers,
>
>       Tim
>