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Message ID: 15935     Entry time: Thu Mar 18 01:12:31 2021
Author: gautam 
Type: Update 
Category: LSC 
Subject: PRFPMi 
  1. Integrated >1 hour at RF only control, high circulating powers tonight.
    • All of the locklosses were due to me typing a wrong number / turning on the wrong filter.
    • So the lock seems pretty stable, at least on the 20 minute timescale.
    • No idea why given the various known broken parts.
  2. Did a bunch of characterization.
    • DARM OLTF - Attachment #1. The reference is when DARM is under ALS control.
    • CARM OLTF - Attachment #2. Seems okay.
    • Sensing matrix - Attachment #3. The CARM and DARM phases seem okay. Maybe the CARM phase can be tuned a bit with the delay line, but I think we are within 10 degrees.
  3. TRX/TRY between 300-400, with large fluctuations mostly angular. So PRG ~17-22, to answer Koji's question in the meeting today.
    • This is similar to what I had before the vent of Sep 2020.
    • Not surprising to me, since I claim that we are in the regime where the recycling gain is limited by the flipped folding mirrors.
  4. Tried to tweak the ASC (QPD only) by looking at the step responses, but I could never get the loop gains such that I could close an integrator on all the loops.

I need to think a little bit about the ASC commissioning strategy. On the positive side

  1. REFL11 board seems to perform at least as well as before.
  2. ALS performance made me (as Pep would say), so so happy.
  3. Whole lock acquisiton sequence takes ~5mins if the PRMI catches lock quickly (5/7 times tonight).
  4. Process seems repeatable.

Things to think about:

  1. How to get the AS WFS in the picture?
  2. What does the (still) crazy sensing matrix mean? I think it's not possible to transfer vertex control to 1f signals with this kind of sensing.
  3. What does it mean that the PRM actuation seems to work, even though the coils are imabalnced by a factor of 3-5, and the coil resistances read out <2 ohms???
  4. What's going on at the ALS-->CARM transition? The ALS noise is clearly low enough that I can sit inside the CARM linewidth. Yet, there seems to be some offset between what ALS thinks is the resonant point, and what the REFL11 signal thinks is the resonant point. I am kind of able to "power through" this conflict, but the IMC error point (=AO path) is not very happy during the transition. It worked 8/8 times tonight, but would be good to figure out how to make this even more robust.
Attachment 1: DARM_OLTF_20210317.pdf  19 kB  Uploaded Thu Mar 18 15:34:47 2021  | Hide | Hide all
Attachment 2: CARMTF_20210317.pdf  89 kB  Uploaded Thu Mar 18 15:35:08 2021  | Hide | Hide all
Attachment 3: PRFPMI_Mar_17sensMat.pdf  45 kB  Uploaded Thu Mar 18 15:35:31 2021  | Hide | Hide all
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