[Tpe] TPE: downstream collimator

[Will Brooks]

  Dear all,

  I will think about it further, but my first inclination is not to have 
a step. A collimator needs to either touch the particles or not, and any 
reduced thicknesses will just increase the exposure to showers. If the 
length of the collimator can be made to be quite a bit longer, then a 
step will possibly help, but I think we would like to have a good solid 
20 radiation lengths for anything where we expect showering particles to 
hit.

  Cristian simulated the entire collimator as tungsten. However, if our 
instincts are correct, only the inner collimator matters. He and I 
discussed this yesterday afternoon, and he was planning to launch a job 
Thursday night with inner collimator made out of tungsten and outer 
collimator made out of Pb. If there are no job crashes, we will have the 
results today (Friday). However, I would not advocate waiting for the 
results before proceeding. The inner W collimator can only help, and 
probably is all that is really needed.

Thanks,

  - Will


On 10/14/10 11:05 PM, Larry Weinstein wrote:
> Dear Folks,
>
> The downstream collimator is a cylinder 40 mm ID, 98 mm OD and about 
> 6" long.  It is currently lead and we would like it to be tungsten 
> (based on Cristian's simulation results).
>
>  1) The downstream collimator will be tungsten ID 40 mm, OD 76.2 mm 
> with a lead jacket ID 76.2 mm, OD 98 mm.  It will take 4-6 weeks to 
> get a bigger piece of tungsten so that the entire piece is made of 
> tungsten.  We do not have that time.
>  2) Dave K suggests that we taper or step the ID of the tungsten to 
> reduce the effects of a possible misalignment and to let the tungsten 
> also be its own clean-up collimator.  Do we want the collimator to be 
> ID 40 mm for the first half (3") and then ID 42 mm for the 2nd half?
>     a) Do we want a step in the collimator?
>     b) If so, where do we want the step (how far downstream)?
>     c) How big do we want the ID change to be?
>
> I will discuss this with Dave Monday (and I will not be available 
> tomorrow).
>
> - Larry
>
> -------- Original Message --------
> Subject: 	collimator at target
> Date: 	Thu, 14 Oct 2010 16:56:55 -0400
> From: 	David Kashy <kashy at jlab.org> <mailto:kashy at jlab.org>
> To: 	Larry Weinstein <weinstei at jlab.org> <mailto:weinstei at jlab.org>
>
>
>
> Hi Larry,
>
> The shop tells me to get tungsten of 4" OD will be 4-5 weeks just for
> the material, I called a place my self and they said 5-6 weeks. I don't
> think we should risk the delay since there is a piece at the shop that
> is 3" od and just over 6" long.
>
> I did have an idea that you might want to consider.
>
> We could make a taper or step in the ID so that slight miss alignment of
> the collimator has less effect that would be something like making the
> first 2, 3 or 4" with 40 mm id and the final 4 , 3 or 2 inches is 42mm
> or 44mm
>
> Let me know
>
> Dave
>
>
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