[Halld-tagger] Beamline / location of solenoid

[Elton Smith]

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.

-- 
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite #16
Newport News, VA 23606
(757) 269-7625
(757) 269-6331 fax