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Entry  Fri Oct 4 02:08:32 2013, Masayuki, Update, Green Locking, FPMI with ALS arm stabilization FPMI_ALS.pdf
    Reply  Wed Oct 23 00:13:30 2013, Masayuki, Update, Green Locking, FPMI with ALS arm stabilization ALSnoise1.pngALSnoise2.pngOLTF.png
Message ID: 9201     Entry time: Fri Oct 4 02:08:32 2013     Reply to this: 9261
Author: Masayuki 
Type: Update 
Category: Green Locking 
Subject: FPMI with ALS arm stabilization 

[Manasa, Masayuki]

We locked MICH with 2 arms stabilized by ALS control.

Measurement

We measured the power spectrum of the LSC-MICH_IN1  at each step so as to know the in-loop noise of MICH. And also we measured the OLTF of MICH loop and the error signal with BS excited at 580 Hz and MICH notch filter at same frequency enabled to obtain the MICH calibration factor.

1. We locked  MICH using the AS55Q error signal and fedback to BS actuator. (Red curve)

2. We locked  MICH and locked both the arms using POX11 and POY11 error signals and fedback to ETMs actuators.(Blue curve)

3. We stabilized both the arms using ALS. We use the ALS error signals and fedback to ETMs actuators. And then we locked  MICH.(Magenta curve)

Attachment

The green and brown curve are the ALS in-loop noise, which is the _PHASE_OUT_Hz calibrated error signals. So for these two curves the unit of vertical axis is Hz/rHz. The other curves are the MICH in-loop noises and these are not calibrated. So for these curves the unit of vertical axis is counts/rHz.

Discussion

The UGF of MICH loop is 10 Hz with phase margin of 45 degrees (measured today). The FPMI noise with ALS stabilized arms is much larger than the FPMI with IR PDH locked arms above 30 Hz. That is because the ALS arm stability is not as good as the stability of PDH locked arms. We have to analyze and verify the calibrated numbers for FPMI + ALS with model.

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FPMI_ALS.pdf
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