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 the 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

• f1=16.88 MHz, f2= 45.02 MHz, f2-f1=28.13 MHz

• List of optical parameters

• PRD 88, 043007 (2013)

1. Daily alignment of the interferometer

Summary of the current status

• Sumary of Alignment Scheme of KAGRA in O3GK JGW-T2112594

Known issues and our plans (highly uncertain)

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

Known issues and our plans (less uncertain)

2. Commissioning and simulations for alignment sensing and control

Commissioning status

• IMC
  • IMC REFL WFS to control IP1 and MCe
    • UGF ~0.1 Hz
  • IMC TRANS DC QPD to control MCo
    • UGF ~0.05 Hz

    • https://klog.icrr.u-tokyo.ac.jp/osl/?r=13916

  • IMMT1T were not used because of scattering lights when PRFPMI is RF locked
  • IMC ASC loops were turned off during O3GK due to excess noise
• WFS and QPDs for the main interferometer
  • REFL and AS are commissioned relatively well and WFS DC centering loops are closed.
  • POP beam was too dirty and WFS are taken out

    • https://klog.icrr.u-tokyo.ac.jp/osl/?r=11506

  • TRX QPDs had strange pitch and yaw coupling

    • https://klog.icrr.u-tokyo.ac.jp/osl/?r=12019

• Xarm
  • REFL WFS17 QPDA1/2 to control SOFT/HARD closed
    • UGF ~50 mHz for SOFT and ~20 mHz for HARD in yaw, ~60 mHz for both HARD and SOFT in pitch

    • https://klog.icrr.u-tokyo.ac.jp/osl/?r=11543

    • https://klog.icrr.u-tokyo.ac.jp/osl/?r=11537

      • https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=10996

  • Sensing matrix measurement with POP, AS, TRX not done
• PRMI
• DRMI
  • ASC did not work including dither.
• FPMI
  • AS WFS28 Q to control BS closed
    • UGF ~30 mHz for yaw, ~80mHz for pitch

      • https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=11061

• PRFPMI

Simulation status

• Optickle

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

  • PRMI, DRMI simulations 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

Known issues and our plans (highly uncertain)

Known issues and our plans (less uncertain)

3. Input mode cleaner alignment sensing and control report