[Halld-tagger] Fixed array counters - corrected

[Franz Klein]

Alex and Richard,

we are working on a stable mounting scheme for the counter from above. 
One way would be to hold the light guides in aluminum cylinders to 
fasten them easily to the support. It is not a problem to have some PMTs 
staggered (2 rows). I am still working on the details.
After comparing test results of various PMTs, it seems most reasonable 
to go with Hamamatsu R9800 (1"). I ordered some (since Ardavan Ghassemi 
(Hamamatsu salesman) first told me that they might have some in store, I 
hoped to have them here this month ... but at the end it will take 8-12 
weeks - talk late Oct./Nov.).

Cheers,
Franz

On 09/11/2012 05:44 PM, Alexander Somov wrote:
>
> I would position all counters from the same side (above),
> it will be more convenient to allign them as well. We'll
> need to place cnt75-143 in two (?) rows.
>
> Cheers,
>        Alex
>
>
> On Tue, 11 Sep 2012, Richard Jones wrote:
>
>> Dan and all,
>>
>> When you mount the fixed array counters, do you foresee them hanging 
>> down from above (like stactites), or sticking up from below (like 
>> stalagmites)? It might be more convenient from the point of view of 
>> cabling to have them above.  It would also help prevent collisions 
>> with the microscope, whose fiber readout is under the focal plane.  
>> We are working on a scheme for shaping the ends of the box to allow 
>> fixed array access to the focal plane immediately below and above the 
>> microscope coverage.
>>
>> -Richard J.
>>
>>
>> On 9/11/2012 4:57 PM, Alexander Somov wrote:
>>> Dear Dan, all,
>>>
>>> I think that the hodoscope rate in the microscope
>>> region is reasonable. I would go with a 4 mm counter
>>> size. The groups of counters also look good for me.
>>>
>>> I would require counters to overlap slightly in the
>>> close-packed region to avoid any acceptance gaps.
>>>
>>> How should we proceed with the counter location with
>>> respect to the focal plane ? Once we decide on this,
>>> we can ask Tim to prepare technical drawing for the
>>> mounting structure. Tim said that they may need
>>> about 1-2 extra cm if we decide to place counters at the
>>> focal plane
>>>
>>> We also need a few counters to cover the acceptance
>>> gap between the microscope scint. and the side plate of
>>> the microscope box.
>>>
>>> Dan, are you going to make some drawings for light guides ?
>>> I would use (straight) fish-tail light guides for
>>> all counters. For small counters (cnt22 + with R<20mm)
>>> we can just use a cylinder as a light guide. It would make
>>> sense to couple the light guides with PMTs in the same
>>> way.
>>>
>>> I would make the light guide about 5-6 inches long.
>>> The fringe field for end-pont counters is below
>>> 70 - 80 Gauss for both Bx and By at Y = 20 cm
>>> (and drops rapidly with Y).
>>>
>>>
>>> Thanks,
>>>          Alex
>>>
>>>
>>>
>>> On Tue, 7 Aug 2012, Daniel Sober wrote:
>>>
>>>> The previous mail, and Point 3 of the file attached to it, did not 
>>>> say quite
>>>> what I meant to.  Please look at the new pdf file instead.
>>>>
>>>> Here's my current best set of counters, with an explanation of the 
>>>> criteria
>>>> used.  Please look especially at point 3.  The important feature is 
>>>> that the
>>>> high-Egamma part of the hodoscope be able to run at GlueX rates.  I 
>>>> have set
>>>> it up so that the counters closest to the Microscope are 4 mm wide, 
>>>> compared
>>>> to the 2 mm Microscope fibers.  Thus no counter in this region 
>>>> counts faster
>>>> than twice the incoherent contribution in a microscope column.  
>>>> Since the
>>>> microscope rate will be limited by the coherent peak, where the 
>>>> total flux is
>>>> ~twice as large, the maximum hodoscope counter rates will be ~ same as
>>>> Microscope column rate. Is this reasonable?  If not, I can easily 
>>>> re-do the
>>>> calculation with a different rate limit.
>>>> Dan
>>>> -- 
>>>> /Daniel Sober
>>>> Professor
>>>> Physics Department
>>>> The Catholic University of America
>>>> Washington, DC 20064
>>>> Phone: (202) 319-5856, -5315
>>>> E-mail: sober at cua.edu/
>>>>
>>
>>
>>

-- 
===============================================================
                   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: 757-269-6672
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