[Halld-tagger] Beamline / location of solenoid

[Tim Whitlatch]

I spoke with Mike Bevins and there is about 2 inches of adjustment on 
the electron dump...  Should be no problem

Tim

Alexander Somov wrote:
> 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.
>>>
>>
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