[Tpe] More on TPE

[David Kashy]

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
>>    
>