LIGO Document E1400071-v1

ECR for adding auto-alignment for ALS

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E - Engineering documents
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Due to the high transmission of the 532 nm ETM coatings the sensitivity to alignment fluctuations and pointing errors is greatly enhanced. This is made worse by the change of cavity geometry between OATS/HIFO-Y and the current Advanced LIGO configuration which results in 3x higher cavity beam motion for the same misalignment. We propose to bring back the ALS wavefront sensors to support automatic alignment.
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Notes and Changes:
pending: Peter Fritschel/ISC will scope out costs and options:
- 1 WFS/end station, wait to see if 2nd WFS is needed
- 2 WFSs per end station
- H1 & L1 only, or 3rd IFO too (even though we don't expect high 532nm transmission for 3rd IFO ETMs, operationally ALS WFSs may be better)
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