[Tpe] More on TPE

[Will Brooks]

Dear Dave,

  A few comments on the calorimeter:

I have estimated the weight at about 3 kg per bar, and we're using 
either 25 or 30 bars. So the weight of the thing for 30 bars is about 
200 pounds, plus any cable weight.

We plan to attach the bars together somehow (i.e., in a box) and pivot 
it in the middle so it can rotate to point skyward, for initial 
calibrations. If this is a major inconvenience, we can just do this 
before and after the run, and have a simpler geometry during the run.

We will use it for dedicated runs in the position indicated, downstream 
of CLAS, but would also like the freedom to move it elsewhere as a 
continuous monitor. Ideally it would be somewhere that it could see 
photons coming from the target. In any case, it must be removed from the 
direct beam during the regular data taking.

It could be hung, or could be positioned further downstream; there is 
some degradation if it is too far back, since it will be measuring 
charged particles that will multiple scatter in the helium or air 
in-between (unless you have vacuum). This is undesirable but not a 
show-stopper.
The downstream beam will be bigger in diameter than normal, since as we 
know it's already fairly big at the target and will multiple scatter 
through the chamber window, etc.

Is there a way to insert the calorimeter into the large steel tube in 
the center of the forward carriage? If there were a safe way to insert 
and remove it, that might be best. The calorimeter is made of modules 
which are 3.8x3.8x45 cm, plus the length of the phototube housing. We 
could stack them in a square array of 5x5, or rectangular array of 5x6. 
(In a pinch, we could even remove the corners of the 5x5 to make it 
closer to a cylinder, but then you have to invent a more complicated 
support system, and also the cosmic ray calibration is a little more 
complicated.) My recollection is that the large steel tube is quite a 
bit larger than that. Another constraint is that Stepan's fiber profiler 
is intended to be in front of it, but it might not fit, I don't know its 
dimensions.

Thanks,

  - Will


On 5/25/10 2:37 PM, David Kashy wrote:
> Hi TPE'ers and others
> Here is an update
>
> As you know we have started the target cell design.
> We have also started a new scattering chamber design to match.
> There are lots of other things that are needed (some could have somewhat
> long lead times marked with **)
>
> Nose Shield for mini torus (** if tungsten is desired)
> Steel Wall
> Steel Wall support **
> 6"OD x 1" thick SST tube(s)
> New stand for Calorimeter **
>
> While reviewing the drawing today I realized that we have used the same
> stand for the downstream dipole triplet magnet and the calorimeter
> behind the forward carriage. This is not possible since we only have
> one. So we will need a different support for the calorimeter! I spoke
> with Doug and he does not like the location just behind the forward
> carriage Apex as shown on
> http://www.jlab.org/~zarecky/TPE/TPE%202010-2012/TPE-SH-3.pdf
> because it blocks egress off the FC. I agree with him and we need to
> find either a new location or method of support. He thought we might be
> able to use the TAC stand at the end of the beam line. Can we remove the
> TAC and use that stand in its current position? Can we move it just to
> the upstream end of the Alcove? Can we find a way to mount it to the
> underside of deck above the beamline on the forward carriage thus not
> blocking egress?
>
> We need to decide if we need vacuum in the beamline down stream of the
> target or will helium do?
> We need more info on protecting the tagger hodoscope.
> We need to decide how to shield the tagger vacuum box.
> We need a design for the shielding at the tagger dump (propsed by Will)
>
> Doug has already gathered much of what we used before and he will
> continue to find things. He and I went over a list of stuff this afternoon.
>
> Thanks
> Dave
>
>
>
> Larry Weinstein wrote:
>    
>> Dear Dave,
>>
>> We have done all our simulations with a 6 cm diameter target cell.
>> The beam is well contained within that diameter, but there is some
>> tail.  We might be able to reduce the diameter by 0.5 cm or at most 1
>> cm.  We can look into that.
>>
>> Beam currents will be 100 pA each of e+ and e- incident on the target
>> windows.  This translates to a dose of about 0.1 MG.
>> 10^-10 A * 3*10^6 s = 3*10^-4 C
>> 3*10^-4 C * 2 MJ/(g/cm^2) = 600 J/(g/cm^2)
>> The beam is spread out over at least 10 cm^2 -->  60 J/g = 60 kJ/kg =
>> 0.06 MGy
>> Double this to account for the two beams to get 0.1 MGy.
>>
>> Radiation damage to the target endcaps is not a problem.
>>
>> - Larry
>>
>> David Kashy wrote:
>>      
>>> Hi All,
>>> Attached is a concept drawing that I'm starting to analyze for the new
>>> TPE target cell.
>>> The material is chosen to be .005" Kapton  for the cylinder and the
>>> upstream and downstream caps. The ring with the ports is Torlon (also a
>>> polyimide) like Kapton. the feed tubes are aluminum as used in all other
>>> targets.
>>>
>>> Please take a look and comment ASAP.
>>>
>>> Questions:
>>>
>>> 1) what is the expected beam spot size at the target?
>>> 2) is there any need to go bigger or smaller OD?  (Smaller is better
>>> since there is less flammable gas but not mandatory)
>>> 3) What is the dose expected for the end caps. (Kapton shows a 24% drop
>>> in ultimate strength and a 5% drop in elongation at 77K when exposed to
>>> 35MGy radiation dose. At 119 MGy the drop in strength is 38% amd
>>> elongation is  35%)
>>>
>>> Thanks
>>> Dave
>>>
>>>        
>>      
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