Hall C Document 980-v1

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Development of a Laser-Based Survey Procedure to Measure the Hall C Target Position

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Holly Szumila-Vance
Updated by:
Holly Szumila-Vance
Document Created:
06 Aug 2018, 11:52
Contents Revised:
06 Aug 2018, 11:52
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06 Aug 2018, 11:52
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The continuous electron beam at Jefferson Lab is used to study the internal structure of nuclei by
studying reactions of the beam with nuclear targets. The beam targets in Hall C are solid or liquid,
and are placed on a movable ladder within a vacuum chamber. The target must be kept at low
temperatures and under vacuum to prevent heating and boiling and to prevent beam interactions
with air. The target ladder moves when subjected to the processes of pulling vacuum and cooling.
This displacement of the target is a large source of uncertainty for both the spectrometer optics
and experimental physics results. An optoNCDT laser can be used to measure this displacement.
The laser was used to take measurements, which were then characterized to determine its
resolution, linearity, stability, and repeatability. From using a similar test set-up to the real Hall
conditions, it was found that the laser has a 0.1 mm resolution, but has associated drifts and offsets
that must be considered before each trial, yielding an overall 0.2 mm resolution in reproducibility.
The laser can be used to effectively measure the position of the target in the experimental hall, but
it must have an adequate “warm-up” period and a linearity check using other known targets at
various distances to determine offsets. With a procedure that characterizes and accounts for all
offsets, this measurement can significantly reduce uncertainties on the target ladder position
during nuclear physics experiments.
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target survey laser
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