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Re: AW: halo muon counter



Dear Peter and Dave,

Please find attached a drawing with the dimensions that will (hopefully) 
allow you to create the apropriate drawing for the workshop. Here are 
some comments with respect to your drawing on the TWiki page:
- I did not yet calculate the h_light. It depends on the length of the 
yet not specified sliding feedthrough.
- The d_plexi is 20 mm for the existing feedthrough. However, Ron told 
me that the mounted PMT is a so called 1.8" and not a 2" one. So we 
probably need to adapt the thickness a bit. However, since the NW40 
connector on the pipe has an inner diameter of 40.8mm there is plenty of 
space for a slightly thicker plexi tube.
- I also drew one of these NW40 connectors which are welded to the 
vacuum pipe. The counter part should have at least the same edge where 
the vacuum clamp is mounted.
- For the length of the vacuum pipe we have the following options:
  + A 360mm long one plus a 650 mm (with one NW40 connector at 200 mm 
from the edge)
  + 1210 mm
  + 800 mm (with one NW40 connector at 180mm from the edge)
I think we should go for the first version since it is similar to the 
actual length of the beginning of the 8" pipe to the target position 
(1020 mm).

Some comments to the existing feedthrough as an orientation for the new one:
- The existing feedthrough has a metal shielding for the plexi with an 
outer diameter of 25.2 mm. In this version plexi and aluminum are 
touching but if you prefer a non touching version with alu wrapping that 
should be fine.
- The outer pipe for the feedthrough with the o-rings has an inner 
diameter of 25.3 mm. So there is only ~0.1mm of space for the two 
sliding parts. Since we might have a thicker plexi tube the diameters 
might change but the relative difference should be the same.
- I didn't manage today to look at the details of the o-rings in the 
feedthrough. But I want to extract one tomorrow and check it's size.
- I haven't thought yet of a good end for the feedthrough where the PMT 
is mounted which could enable us to prevent the PMT from being sucked 
in. But you (Peter) already had something in mind with the set screws, 
right.

Today I also talked to Mr Bugmann from the workshop east. He immediately 
told me that they are extremely busy until October. However, if we come 
with good drawings he can better estimate the time they need. If they 
only had to cut the plexi tube and the metal shielding it would be a  
few days only. The outer feedthrough that needs to be milled adds some 
more days. I already checked with Mr Baumann from the Hallendienst and 
he agreed that they can do the vacuum tight welding of the two NW40 
connectors next week. The milling could be done in the workshop west but 
I first need to ask for their capacities. So we should estimate 1-2 
weeks for that being done at PSI.

Well, I hope that these information are sufficient to bring up a first 
version of a design. I'm sure we need another iteration tomorrow. I'll 
be still online for about half an hour in case I have forgotten to 
provide some necessary information. Tomorrow I'll be looking around for 
the PMTs and other mechanics and with a fresh mind I can review any 
drawings.
Best greetings
Peter

Attachment: HaloCounter.ppt
Description: MS-Powerpoint presentation