Sascha,
Thank you for this thorough study that you have done, and the excellent
report on your results. I have the following comments.
- You have decreased the diameter of the secondary collimator from
10mm to 6mm. This decision means that either we must make the
secondary collimator exchangeable, or we give up considerable
flexibility in the ability to open the beam aperture. It is useful to
have the ability to do that to check alignment during beamline setup
and commissioning. It also has an impact on our ability to run at
higher tagging ratios for efficient unpolarized running. So my
question to you is, how much do we gain by that reduction? I know you
want to shadow the support structure of the Liq. H2 target. Is it
worth increasing the cost and complexity of the beamline by making the
secondary collimator removable? If we need a 6mm secondary to run
GlueX under optimum bg conditions, I see three options. Obviously I
prefer option 3, but we need to justify the cost.
- reduce the aperture to 6mm and design our alignment and run
plan around that constraint
- reduce the aperture to 6mm, but plan to go into the cave, open
the vacuum system and manually remove or replace the collimator with a
different one when the need arises.
- install an in-vacuum collimator ladder at the secondary
collimator station, for maximum flexibility.
- It might be worth taking Fig. 16, panel 3 to the electronics
guys and ask if that high flux of low-energy gammas in the area of the
electronics racks is a concern to them. It is probably not enough for
them to care, but it is 5 orders of magnitude above cosmic levels so I
don't want to assume anything.
Richard Jones
Alexander Somov wrote:
Pine.LNX.4.58.0807090953400.19987@ifarml1.jlab.org">
Dear colleagues,
I put a draft of the document describing simulation of collimator
cave and pair spectrometer background to
http://www.jlab.org/Hall-D/software/wiki/index.php/Collimator_cave_background
(I will place it to the DocDB later)
Cheers,
Sascha
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