[G14_run] Natalie's talk at 10-12-12 meeting - collimators

[Franz Klein]

Andy,
years ago we decided to go with a smaller diameter of IBC and target to 
achieve better polarization and temperature stability. The focus on the 
experiment were extraction of polarization observables, not cross sections 
... which can be done much better with long LH2, LD2 targets.
Of course, it is nice to subtract the corresponding cross sections to 
check the systematics of the asymmetries, but that was not the focus!

We could have used a larger collimator for the circular photon setting. 
For the plane-polarized photon setting we need anyway the 2.0mm 
collimator.

Greetings
Franz

On Wed, 17 Oct 2012, A.M.  Sandorfi wrote:

> Folks,
> As Eugene mentioned, Linear polarization from diamond required a 2.0 mm
> collimator to define angles and maximize the photon polarization. This
> produced a spot of about 7.5 mm OD on target and our cell was 15 mm ID.
>
> For circular running we just copied the g9 conditions and used the 2.6 mm
> collimator. But we could easily have made 25 mm ID targets so, while it's
> unpleasant to think of these things now, I guess for circular running in g14
> we could have used a larger collimator, which would have given us more flux
> on target - sigh!
>
> Andy
>
>
>
>
> On 10/17/12 12:57 PM, "Eugene Pasyuk" <pasyuk at jlab.org> wrote:
>
>> Reinhard,
>>
>> This is because for g14 run we collimated (2.6 mm for circularly polarized and
>> 2mm for linearly polarized) photon beam while for g1c and g11 the beam was
>> uncollimated.
>> We used small collimator to make sure the beam does not hit target cell walls.
>> The inner diameter of the HD cell is 15 mm. With this collimation beam spot
>> size on target is bout 10 mm. The targets for g1c and and g11 had diameter 60
>> and 40 mm respectively.
>>
>> -Eugene
>>
>> ----- Original Message -----
>>> From: "Reinhard Schumacher" <schumacher at cmu.edu>
>>> To: "g14 run" <g14_run at jlab.org>
>>> Sent: Wednesday, October 17, 2012 12:47:17 PM
>>> Subject: [G14_run] Natalie's talk at 10-12-12 meeting
>>>
>>> Hi Natalie,
>>> I liked looking through the slides of your talk last Friday, the one
>>> at
>>> the Collaboration meeting I missed.  There is some interesting new
>>> material.
>>>
>>> My immediate question is about slide 13 showing a measurement of the
>>> beam line transmission function, based, I assume, on an analysis of
>>> the
>>> TAC data from a normalization run.  Why is the transmission
>>> efficiency
>>> as small as 35%?  For g1c and g11 the transmission fraction was much
>>> larger.  Is it because of the size of the collimator?  If that is the
>>> case, why did we use such a small collimator?
>>>
>>> Anyone can comment on this of course, not just Natalie.
>>>
>>> Cheers,
>>> Reinhard
>>>
>>>
>>> --
>>> ___________________________________________________________________
>>> Reinhard Schumacher         Department of Physics, 5000 Forbes Ave.
>>> Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A.
>>> phone: 412-268-5177         web: www-meg.phys.cmu.edu/~schumach
>>> ___________________________________________________________________
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===============================================================
                   Franz J. Klein, Associate Professor
                   CUA, Department of Physics
                   Washington, DC 20064
   office: Hannan Hall 206          phone: 202-319-6190
   or: Jefferson Lab,CC F-243       phone: 757-269-6672
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