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David Buscher added At_installation_time_the_beam__.tex
about 8 years ago
Commit id: 9a2c406a7092b2c935d7d9710d848eeb87c25a0f
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At installation time, the beam emitted by the UTM injection system needs to be aligned with the UTM inner axis. The accuracy of this alignment is that needed to keep the beam aligned with the pupil image independent of the inner axis rotation angle: this amounts to a precision of about 0.5\,mm in shear and 0.2\,milliradians of tilt. The laxness of this constraint means that this alignment needs to be done only once, as thermal drifts in alignment of this magnitude are not expected during the course of operation (of course, it would not harm to check this from time to time). A number of techniques can be used for the initial alignment, but manual alignment using a theodolite inserted in the UT output beam looking at both the telescope pupil and the injected light is one option.
The initial alignment of a beam train takes place using the BCA primary fiducial as before (although there exist additional options to use the UTM light injector in addition to or instead of the primary fiducial for this task, these will not be discussed further here).
