LIGO Document T1300688-v2

ALS Noise Measurements and Model for HIFO-Y

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T - Technical notes
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Our measurements show a residual RMS of approximately 5 Hz for End-Y Half Interferometer (HIFO-Y). This matches well with the ALS model prediction. The dominant noise sources come from acoustic coupling at frequencies of around 100 Hz and suspension motion at frequencies below 5 Hz. The model indicates that with a reduction in acoustic noise by a factor of 10, the UGF of the CARM feedback control can be increased to 1 kHz while keeping under the noise requirement of 8 Hz. The model also highlights other contributing noise projections.

Besides noise projections, the ALS model is a linear control model that provides one with the ability to run several transfer functions of the servo loops required for the Arm Length Stabilization (ALS) system in HIFO-Y. This document describes the model and noise analysis in detail.

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