[Halld-tagger] Beamline / location of solenoid

[Tim Whitlatch]

Hi Elton,

It is known that the other halls had settled over time. We will not be 
able to adjust the solenoid once it is completely installed. The BCAL is 
along for the ride and cannot be adjusted after it is installed. The CDC 
and FDC can be pulled out and adjusted if needed, but only to about the 
5 mm level.
Our beam pipe coming into the collimator has plenty of clearance so 
should be able to account for any settling. The collimator can be 
adjusted along with the solenoid settling. If the tagger settles more 
and we need to adjust it, that may be an issue depending on the dump 
acceptance. I believe the dump can handle a relatively large variation. 
I will check with Mike Bevins.

If the tagger is in need of adjustment over time, this could be 
relatively easy (to the 10 mm level).

Hall D has been in place for almost 9 months. We can have Chris check 
how much it has settled already. If the tagger is expected to settle 
more, we may not wish to set the solenoid high.

This definitely deserves more discussion.

Tim

Elton Smith wrote:
> Hi Tim,
>
> Tom was meeting with Chris Curtis from the survey group to discuss the 
> procedure for aligning the solenoid magnet, presently scheduled for 
> mid September. The question came up regarding possible settlement of 
> the Hall D building and whether we should take specific adjustments 
> for that.
>
> Assumptions:
> 1. We assume that changing the height of the magnet once installed 
> will be difficult
> - It would be useful to find out if any adjustments are possible, 
> e.g.  is it possible to lower it?
> 2. We assume that there would be some possible (vertical) adjustment 
> to the electron beamline at the time of installation. This should be 
> checked with beam transport and bring them into the discussion loop 
> when we have come up with a strategy.
>
> Suggested strategy and comments:
> 1. Align magnet to predetermined  height and align north/south.
> - Do we want to set the initial height of the magnet above nominal 
> with the expectation of settling?
> - I spoke to Rebecca Yasky. She said that Hall D is in fact on the 
> Yorktown Formation, so we might expect little settling. However, the 
> geological study (now 10 years old) expected less than 1 inch 
> settlement over the lifetime.
> - Hall D is not dewatered, so it is possible that there could be 
> movements due to ground water level.
> - The tagger building is not on the Yorktown, so it may actually have 
> more settling.
> 2. At the time the electron beamline and tagger magnet are being 
> installed, re-survey the position of the beamline in the collimator 
> hut and the height of the solenoid. Install the electron beamline and 
> tagger to correspond to the as-measured collimator and solenoid 
> locations.
>
> Note: The angle of the beam is adjustable and may be able to take up 
> some displacements of the collimator relative to the electron beamline
>
> Feedback is welcome.
>
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