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So far, WFS and QPD loops for IMC, PRMI and FPMI are mostly closed. For PRFPMI, we didn't have much time for ASC commissioning. Also, we had ugly beam shape at POP and POP WFS were not commissioned at all so far. TRX QPDs had strange pitch and yaw coupling which needs further investigations. Achievements for different interferometer congifurations are summarized below. So far, WFS and QPD loops for IMC, PRMI and FPMI are mostly closed. For PRFPMI, we didn't have much time for ASC commissioning. Also, we had ugly beam shape at POP and POP WFS were not commissioned at all so far. TRX QPDs had strange pitch and yaw coupling which needs further investigations. Achievements for different interferometer configurations are summarized below.

Note that most of the loops indicated "closed" were "once closed" and were not stable enough to implement them in the guardian. Even if the loop was once closed, it was not reproducible. We suspect that linear ranges are too small and/or zero-crossing points are dependent on the interferometer alignment (for example, simulated WFS signals are distorted if we include inhomogeneity of ITMs [[https://journals.aps.org/prd/abstract/10.1103/PhysRevD.100.082005|PhysRevD.100.082005]]). We hope we can improve the situation once we establish reproducible daily alignment procedure.
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Commissioning towards O3 and RSE trial mostly focused on length sensing and control, and little time was occasionally allocated for ASC, when there was some spare time. For the commissioning towards O4, we should spend more time for ASC to achieve a stable lock. Commissioning towards O3 and RSE trial mostly focused on length sensing and control, and noise hunting towards achieving the 1 Mpc goal. Stability of the lock was not considered seriously and little time was occasionally allocated for ASC, when there was some spare time. For the commissioning towards O4, we should spend more time for ASC to achieve a stable lock.
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  * Measure the sensing matrix and compare it with analytical calculations and simulations
  * Hold the lock of IMC with ASC for a duration of longer than 2 hours continuously
   * Make sure that suspension alignment drift is smaller and the length noise is smaller when the ASC loops are on.

External Review for interferometer alignment controls (August 2021)

Purpose

From February 25 to April 21, 2020, KAGRA performed its first observing run for 4 weeks with power-recycled Fabry-Perot-Michelson (PRFPMI) congifuration. The sensitivity during the April run with GEO600, dubbed O3GK, was at the binary neutron star range of 0.5-0.7 Mpc. From July 13 to October 13, we had an intense commissioning period to try locking the full resonant sideband extraction (RSE) interferometer. We had many achievements during that period, but we have never achieved the full RSE lock yet.

During the O3GK run and the RSE trial, we faced several issues related to the interferometer alignment. The sensitivity of KAGRA depended very much on the alignment, and the best sensitivity could be achieved only when the expert aligned the interferometer manually. Almost no alignment sensing and controls (ASC) loops where closed, except for a few dither alignment loops in the power recycling cavity (PRC).

The purpose of this External Review is to receive comments from LIGO/Virgo interferometer experts on our plans to improve such situations. We would like to know if the issues we are trying to solve are reasonable, and if our plans are sound. We would also like to find out what are the issues we haven't identified yet. Finally, we would like to prioritize the works in the order of importance for a stable full RSE lock with ASC.

Agenda

  1. Daily alignment of the interferometer
    • summary of O3-RSE trial situation and improvement plans
  2. Commissioning and simulations for alignment sensing and control
    • summary of current situation and plans, focus on global controls using wave front sensors (WFS) and QPDs
  3. Input mode cleaner alignment sensing and control report
    • report from current on-site works

Basics of KAGRA interferometer

1. Daily alignment of the interferometer

1-1. Summary of the current status

The alignment scheme used for O3GK and RSE trial is summarized graphically in JGW-T2112594.

We started the daily alignment from the Xarm using the green beam. The Xarm is locked with green, and ITMX and ETMX alignments were tuned to center the beam on them, by monitoring camera (Tcam) images of the HR surfaces by our eyes. PR3 dither alignment was also done at this step to maximize the green transmission. The green injection from the back of PR2 was also tuned manually using a steering mirror (POP POM) at the back of PR2 occasionally.

We then proceeded to align IR beam to the Xarm by locking the Xarm with IR, and maximizing the IR transmission with IMMT2 and PR2 dither alignment.

Next, we aligned PRMI by maximizing POP90 with PRM and BS dither alignment. Somehow, when we do the Yarm alignment before PRMI, MICH fringe was not good.

We then aligned Yarm with ETMY dither alignment. By monitoring camera (Tcam) images of the HR surface of ETMY by our eyes, ITMY alignment was also tuned occasionally to center the beam on ETMY. When ITMY was moved, we went back to PRMI alignment again. Note that beam position on ITMY is not checked in this scheme.

Then, Yarm green beam is aligned by maximizing green transmission with SR3 dither alignment. The green injection from the back of SR2 was also tuned manually using a steering mirror (POS POM) at the back of SR2 occasionally.

And Finally, the single bounce beam from ITMY is aligned to OMC by maximizing OMC transmission with OMMT2 and OMC dither alignment.

1-2. Known issues and our plans (highly uncertain)

  • Issue 1
    • Plans ...
  • Issue 2
    • Plans ...

1-3. Known issues and our plans (less uncertain)

2. Commissioning and simulations for alignment sensing and control

2-1. Commissioning status

So far, WFS and QPD loops for IMC, PRMI and FPMI are mostly closed. For PRFPMI, we didn't have much time for ASC commissioning. Also, we had ugly beam shape at POP and POP WFS were not commissioned at all so far. TRX QPDs had strange pitch and yaw coupling which needs further investigations. Achievements for different interferometer configurations are summarized below.

Note that most of the loops indicated "closed" were "once closed" and were not stable enough to implement them in the guardian. Even if the loop was once closed, it was not reproducible. We suspect that linear ranges are too small and/or zero-crossing points are dependent on the interferometer alignment (for example, simulated WFS signals are distorted if we include inhomogeneity of ITMs PhysRevD.100.082005). We hope we can improve the situation once we establish reproducible daily alignment procedure.

2-2. Simulation status

  • Optickle

    • FPMI, PRFPMI, SRFPMI, DRFPMI (BRSE) sensing matrix simulations with imperfections done JGW-T1910359

    • PRMI, DRMI simulations, implementation of f2-f1 signals not yet
  • FINESSE

    • For LSC without mirror maps, GUI for simulations with any interferometer configurations done JGW-T2012132

    • Working on ASC integration
    • Also input mode cleaner (IMC) ASC simulations and analytical calculations on going independently

2-3. Strategies for commissioning

Commissioning towards O3 and RSE trial mostly focused on length sensing and control, and noise hunting towards achieving the 1 Mpc goal. Stability of the lock was not considered seriously and little time was occasionally allocated for ASC, when there was some spare time. For the commissioning towards O4, we should spend more time for ASC to achieve a stable lock.

Our planned timeline and goals for each step are summarized below (timeline based on JGW-G2113055). Full automation of the lock acquisition and daily alignment process should also be established at each stage.

  • IMC (May - August 2021)
    • Measure the sensing matrix and compare it with analytical calculations and simulations
    • Hold the lock of IMC with ASC for a duration of longer than 2 hours continuously
      • Make sure that suspension alignment drift is smaller and the length noise is smaller when the ASC loops are on.
  • Xarm (mid-August - mid-November 2021; ~12 weeks)
    • Find out the reasons for ugly POP beam
    • Investigate TRX pitch and yaw coupling issue
    • Check if REFL WFS, POP WFS, AS WFS and TRX QPD give consistent sensing matrices with simulations
      • Check the polarization content at each port when Xarm is locked/unlocked, cross check with FINESSE (birefringence) model
    • Hold the lock of Xarm in IR with ASC for a duration of longer than 2 hours continuously
      • SOFT and HARD controlled with REFL/AS and TRX
      • Make sure that suspension alignment drift is smaller when the ASC loops are on
  • Yarm (November 2021 - mid-January 2022; ~9 weeks)
    • Check if REFL WFS, POP WFS, AS WFS and TRY QPD give consistent sensing matrices with simulations
    • Hold the lock of Yarm in IR with ASC for a duration of longer than 2 hours continuously
      • SOFT and HARD controlled with REFL/AS and TRY
      • Make sure that suspension alignment drift is smaller when the ASC loops are on
  • FPMI (January - February 2022; ~8 weeks)
    • Note that we haven't try to lock FPMI in air before
    • Check the polarization content at each port, mode content at AS, cross check with FINESSE (birefringence) model
      • Compare them with a simple Michelson configuration to see Lawrence effect
    • OMC alignment commissioning
    • Hold the lock of FPMI in IR with ASC for a duration of longer than 2 hours continuously
      • CHARD controlled with REFL, DHARD controlled with AS
      • CSOFT and CHARD controlled with TRX and TRY
      • BS controlled with AS RF28
  • Center area evacuation (mid-February - mid-March 2022; ~4weeks)
    • Before evacuation, we at least want to check PRC/SRC Gouy phase/length, possible beam clipping (for POP), and decide SRM transmission (T=0% or T=30% 2-inch mirror)
  • PRMI (March - April 2022; ~7 weeks)
    • PRMI lock should be tried before the center area evacuation (we were able to lock PRMI in air before)
    • Check PRC Gouy phase and length (inconsistent results so far)
    • Hold the lock of PRMI in 1f or 3f signals with ASC for a duration of longer than 2 hours continuously
      • PR mirrors controlled with POP
      • BS controlled with AS RF28
      • Make sure that suspension alignment drift is smaller when the ASC loops are on
  • PRFPMI (May - June 2022; ~8 weeks)
    • Hold the lock of PRFPMI with ASC for a duration of longer than 2 hours continuously
      • CHARD controlled with REFL, DHARD controlled with AS
      • CSOFT and CHARD controlled with TRX and TRY
      • PR mirrors controlled with POP
      • BS controlled with AS RF28
      • Make sure that suspension alignment drift is smaller when the ASC loops are on
  • Towards DR
    • Check SRC Gouy phase and length (inconsistent results so far)
    • Examine the mode-hop criteria
      • Which mirror affects most and how much angular motions are tolerable

3. Input mode cleaner alignment sensing and control report

References

KAGRA/Subgroups/MIF/ExternalReview2021 (last edited 2021-08-26 00:30:15 by haoyu.wang)