[Halld-tagger] Beamline / location of solenoid

[Alexander Somov]

Hi Tod,

We have a discussion about possible settling  of the
experimental Hall-D and the tagger hall. Most components
in the tagger hall and the collimator cave are placed on
vertically adjusted cartridges, so that the vertical alignment
of them is possible in some range. However, the Solenoid
magnet, positioned in the experimental hall cannot be
adjusted vertically. Therefore, we might need to change
the photon beam trajectory and make the beam go through the
center of the target.

Do you know what our possibilities are in terms of changing
the electron beam parameters, i.e.,changing the incident angle
of electrons on the diamond crystal and the  vertical beam position ?

We don't know now what the possible settling could be  (might be 1/2 '').
The solenoid magnet is placed  about 22 m downstream from
the primary (3.4 mm diameter) photon collimator ( 76 m + 22 m = 98 m
from the diamond radiator).

Thanks a lot,
             Alex


On Wed, 24 Aug 2011, Tim Whitlatch wrote:

> 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.
>> 
>