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will be approximately 0.003".
The vacuum can then be seal and the nose installed. The target must be positioned
with the roots pumps connected and tied down permanently. This survey is done
in conjunction with the table tuning that the target magnet sits on.
Long term running information will also provide X, Y positioning measured
from averaged vertex reconstruction but this takes at least 1 month of data to produce and only give the mean with a very large variance. The precision in
the target cell to beamline positioning needs to be good to mitigate
large absolute errors while running. This is estimated to be on the sub-millimeter level (based on simulations being confirmed). There are several factors that can lead to false asymmetries relating to this precision. There can be a bias produced in the detector if the beam is off center. There can also be less polarized scattering if the beam is not aligned and missing part of the target material (beam profile dependent, also being checked).
There can be greater scattering off the aluminum ladder on one side as compared to the other. Most of these manifest from X being off but if Y is off over 1 mm then the same issues start to manifest with the ladder as well but this may not result in false asymmetry and only result in additional heat load to the coils.
Once the close survey is complete the only additional information must
come from radiography or from running the beam.
An X-ray survey while cold would be the next step if possible. We may not needed it if we achieve good results from the above. It may also be possible to use a special insert with fitted with film to check beam position on a special target insert without depending on the magnet or nose having LHe in them. We might also find something that discolors or burns in the beam so we can make an insert that will be use over the experiment to confirm beam position over time.
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Documents:
First Survey: Dock Survey