Re: Tagger design

[Franz Klein <fklein@jlab.org>]

Richard and Tim,

in the updated design the fixed array is 30cm displaced from the focal 
plane. Last May I didn't have any drawings from Richard ... but that has 
changed! It doesn't make sense to have the microscope (high resolution 
device) behind the fixed array (low resolution device).

Franz


On Mon, 29 Sep 2008, Richard Jones wrote:

> 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
>> 
>
>

===============================================================
                   Franz J. Klein, Associate Professor
                   CUA, Department of Physics
                   Washington, DC 20064
   office: Hannan Hall 206          phone: 202-319-6190
   or: Jefferson Lab,CC F-243       phone: 757-269-6671
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