[Kenta, Yuzu] (LockLossWork)
We checked the signals related to MICH, PRCL (IN1, OUT, RFPD signals), and REFL PDA1 DC signal during the cavity scan (LSC_LOCK guaridn = FIND_FINE_IR_RESONANCES). Fig1 shows several signals at the time without the glitch on MICH_OUT and PRCL_OUT. Fig2 shows the same signals at the time with the glitch(shown in the original post). We found

• The peak-to-peak amplitude of REFL_PDA2_RF51_Q (MICH, yellow) became larger 3.8 -> 27.9.
• The peak-to-peak amplitude of REFL_PDA2_RF135_I (PRCL, sky blue line) became larger 1.6 -> 11.1.
• The power dreduction of REFL_PDA1_DC (because REFL_PDA2_DC is unavailable) became smaller 5.77 -> 3.8.
  • When we correct the power reduction by taking account into the IRX power, we expect the REFL_PDA1_DC will be 5.7/18.7*8.1 = 2.4. The current power reduction is 3.8.
  • Ushiba-san told us that the the alignment of PRCL might be not good and the PRCL cavity might be lossy. He suggest the intitial alignment might solve the issue.
• We are still not sure what the critical cause is...

I listed up the activities on 8/29 and the status of IFO locking.

• - 05:16 : IFO kept locked with ASC from last night
• 05:16 : Unlocked intentionally for Pcal-X alignment (klog 30906)
• Before morning meeting: Not sure. Initial alignment?
• 09:23 : Stopped IFO work and started ISS work
• 13:04 : Resume IFO work, PRFPMI_RF_LOCKED for recording a good alignment
• 13:28 : Requested DOWN intentionally, locked IFO as PRFPMI with 1f signal without ASC
• 14:32 : ASC engaged (PRFPMI_RF_LOCKED)
  • ISS work (implementation of whitening filters)
• 16:11: IFO down, started VIS work
  • Designed NBDAMP filter for 1.67 Hz
  • Implemented in ITMY
• 20:06 : Started IFO work again
• 20:48 : Started DC readout trial
• 29:54 : IFO down, after that we failed in IR handover

Some important signals for lock acquisition on 8/29 0:00 - 8/30 0:00 are shown in Figure1.

I checked these signals during IR handover. Figure2, Figure3, and Figure4 show the time series at 06:11 (after PCAL Y work), 13:08 (after ISS work) and 20:10 (after VIS work). It seens that MICH and PRCL glitch appeared after the VIS work.

Silimar phenomenon was reported last year (klog 26074). That post concluded that the cause of the instability is glitches in DARM signal. on the other hand, in the current situation it seems no glitches in DARM signal when IR is close to resonance as shown in Figure5.

[Kenda, Yuzu]

• We checked the SDF of LSC, LSC2 by requesting the LSC_LOCK guardian. The FM1 and FM2 have been changed since August 18, as reported in klog30867. (FIG1)
  • At 2024/08/29 4:35:00 UTC and 13:30:57 UTC, there is no difference on switches on these filter banks. (FIG2)
• I checked the filter bankds. There was no obvious difference on the switches, gain, the demodulation phase.
  • FIG3: REFL_PDA2_RF51 (MICH). The upper panel shows the time without glitch (4:35:00 UTC). The bottom panel shows the time occuring the glitch ( 13:30:57 UTC).
  • FIG4: REFL_PDA2_RF135 (PRCL). The layout is same as FIG3.

Ushiba, Yuzurihara, Tanaka

I measured the spectra of PRCL and MICH error/feedback signals with various states. Also, we measured the oplev signals related PRMI. Fig. 1 and 2 show the results. The red line shows the spectra when the IR beam was flashing in arm cavities and PRMI was locked with 3f signals, DARM/CARM were lockd with ALS. The blue line are the spectra when the IR beam was not flashing in arm cavities by applying the CARM offset intetionally and PRMI was locked with 3f signals, DARM/CARM were lockd with ALS. The green lines are when PRFPMI was locked with 3f signals.

As you can see, there seems not to be significant difference between blue and green lines in both figures. On the other hands, when the IR beam were flashing in ARM cavity, large bumps appeared in red spectra of fig.1 from several Hz to 100 Hz. And there are strong coherence between the MICH and PRCL feedback signal in this region. So this indicates there is the large coupling between MICH and PRCL.

First, we attemped to change the PRCL UGF and saw whether the bumps in the MICH feedback signal was changed. Fig. 3 shows the results. When we halfed the UGF, then the bumps got larger (black). On the other hands, when the tripled the UGF then the bumps got slightly smaller (green).

Second, we attemped to subtract the PRCL signal from the MICH signal using the PRCL signal. the red line shows the result and indicated that this method is not effective. 

Next, we try to check the phasing of 3f PDs

Fig.1 shows the current RAM offset in REFL PDs when the beam was reflected from PRM directly.

RF17 and RF56 seem to be still large (>400 cnts). RF45s seem to be somehow smaller than previous ones in klog308806.

On the other hands, there are very small offsets in the 3f signals.

I measured CARM error signal (CARM_SERVO_{FAST, SLOW}_DAQ) and checked coherence between MICH and PRCL signals as shown Figure1.

Top two plots are power spectrum of CARM error signals with various IFO status, PRMI by 3f locking with the arms flashing (red), without arm flashing (blue) and PRFPMI by 3f locking (green). When the arms were flashing, CARM error signals got smaller by ~ 6 times. This implies that when the arms were flashing the sensor efficiency got smaller (or the signals were saturated?).

Bottom two plots are coherence between CARM_SERVO_FAST_DAQ and LSC_{MICH, PRCL}_IN1. Coherence came up only when the arms were flashing.

I think the glitches may related to the CARM signal because both 3f signals arealso sensitive to CARM signal, but I'm not sure about the actual mechanism.

[kTanaka, Ushiba]

We noticed that the phasing of REFL PDA2 RF51 and RF135 did not seem to be done with PRMI.
So, we checked them.

Figure 1 shows the spectra of REFL_PDA2_RF_51_{I,Q} signals with 94.125 Hz MICH excitation..
The references show the spectra before the phase rotation (102.22 degrees) and the current values show the spectra after the phase rotation (26.82 degrees).

Figure 2 shows the spectra of the REFL_PDA2_RF_135_{I,Q}signals with 94.125 Hz PRCL excitation.
REF0 and REF1 show the spectra before the phase rotation (86.92 degrees) and REF6 and REF7 show the spectra after the phase rotation (129.92 degrees).

So, PD phasing seemed to be not good for both PRCL and MICH.
Since this is the first time we have performed phasing after O4a with PRMI, we are not so sure when the mis-phasing occurred.

After phasing, we tried PRFPMI lock but there are still PRMI glitches are existing when the arms are flashing.
So, further investigation is necessary.

Note:

During phasing, we noticed that MICH has a large offset.
Figure 3 shows the MICH error signals and POP90 signals after RF51 phase rotation.
As you can see, POP90 signals became obviously large when the MICH error signal was changed from 0 to -20 (roughly in units of nm).
We are not so sure what is the source of this offset but if it comes from RF AM, it could be a critical because REFL PD power was drastically changed when arms are flashing for LOCK acquisition and it would cause large offset change of MICH.

We kept new phase values even though PRFPMI could not be locked.
So, if you find some problems, do not hesitate to revert them.
In addition, we also keep K1:LSC-MICH1_OFFSET 20 to get good POP90 with current RF51 phase.
So, if you revert the phase values, please also revert the MICH offset values.

Also, we didn't measure the PRCL and MICH OLTF after the phase rotation, so it is necessary to measure them.

CARM OLTF was also measured during the state of PRFPMI_LOCKED_WITH_3F.

Date: 2024/9/3
With KTanaka, Yokozawa, Ushiba, Michael

Summary

• We minimized the MICH offset and adjusted the demodulation phase of REFL_PDA2_RF51 to see if the glitch issue would be improved, but it was not improved.
• Then, we adjusted the phase to minimize the glitchs on MICH and PRCL loops. The final phase was 76.220 deg.
• After the adjustment, we could reach PRFPMI_LOCKED_WITH_3F state and measured OLTFs.
• (The references on the attached files are old measruement data, which may have different situation. So we can not take them as the references.)

Details

• At first, we make the demodulation phase of LSC_REFL_PDA2_RF51 to be back to 102.220Hz, which was changed yesterday.
• Adjustment of the phase with the signal of MICH after set MICH1 OFFSET back to 0.0, which was changed yesterday.
  • State: PRMI_3F_LOCKED with misaligned ETM.
  • Minimize MICH offset
    • Guardian: LSC_LOCK -> DOWN, VIS_ETMX -> MISALIGNED, VIS_ETMY -> MISALIGNED, VERTEX -> PRMI_3F_LOCKED
    • MICH1 OFFSET = 20.0 -> 0.0 (at the day before yesterday, it was 0.0.)
    • This is because we don't want the glitchs for this measurement. If the ARM flashing, the glitchs happen.
  • When we shake MICH, we needed to add a notch on PRCL1 FB.
  • We use 94.125Hz at MICH1 EXC to shake the MICH error and use it as a reference to obtimize the phase.
    • If the PRC Trans laser power is at the top point, there would be a signal at double the frequency and the signal at the freq would be smaller(dissappers).
  • The current phase is 102.220 deg
  • Change the RD rotation of LSC_REFL_PDA2_RF51, which is the phase.
    • 121 deg looks to be the optimized value. (121.220deg)
    • We monitored the TF from MICH OUT to the RF51.
  • Measured MICH OLTF with the PRMI_3F.
    • diaggui file: /users/Commissioning/data/DARM/2024/0903/DARM_OLG_PRMI_3F.xml
    • Fig001
  • Requested PRMI_3F_LOCKED from LSC_LOCK to check if the glitchs are better.
    • There are still many glitchs.
• Try to change the phase by whaching glitchs.
  • When the phase is 76.220deg, we could reach PRFPMI_LOCKED_WITH_3F with LSC_LOCK.
  • Check pahing of PRCL.
  • Measurement of OLTFs with PRFPMI_LOCKED_WITH_3F
    • diaggui template: Commissioning dock -> Right bottom green botton -> ? OLG
    • DARM: /users/Commissioning/data/DARM/2024/0903/DARM_OLTF.xml
      • fig002
    • MICH: /users/Commissioning/data/MICH/2024/0903/MICH_OLG.xml
      • fig003
    • PRCL: /users/Commissioning/data/PRCL/2024/0903/PRCL_OLG.xml
      • fig004
  • Measurement of OLTFs with ENGAGE_WFSDC: 1F lock
    • MICH: /users/Commissioning/data/MICH/2024/0903/MICH_OLG_ENGAGE_WFSDC.xml
      • fig005
    • PRCL: /users/Commissioning/data/PRCL/2024/0903/PRCL_OLG_ENGAGE_WFSDC.xml
      • fig006

Additional information:

After locking the PRFPMI, I measured the RF51 I/Q signals with PRCL excitation at 94.125 Hz to understand the current demodulation phase.
Figure 1 shows the cross spectrum of RF51Q/RF51I.
Since Q/I values increased with the "optimal" demodulation phase for PRMI glitches, PRCL to MICH coupling seems increased.
So, new "optimal" demodulation phase is diffrent from the phase that minimizes MICH offsets, minimizes PRCL to MICH coupling, and maximizes MICH signals.