I updated the Guardian for the DRMI ADS preparation so that the following parameters are automatically set:

• IMMT2 excitation frequency, amplitude, and phase
• Common filters for the BP and I signals
• Notch filters

I modified LOCKING_DRMI_1F state as follows (see also fig1).

1. Change gains of MICH1, PRCL1, and SRCL1 filter bank to 1 to avoid kick of the suspension during the lock acquisition (self.counter = 0).
2. Increasing gains of MICH1, PRCL1, and SRCL1 fiter bank to 9, 1.7, and 1.4, respectively after DRMI is locked (self.counter == 2).
3. Turning off MICH2, PRCL2, and SRCL2 gains when suspension waskicked during the lock acquisition to avoid additional kick before calm down (self.counter == -1).

Ushiba, Hirose, Tanaka

We modified IMMT2 ADS so that we can implement resG filters in PRCL, SRCL, and MICH controls to suppress the peaks at IMMT2 dither frequencies in their error signals.

We changed the dither frequencies from 30.125 Hz and 32.125 Hz to 9.125 Hz and 19.125 Hz and performed the phasing for these frequencies (fig.1).

According to the phasing results, we set the demod. phases. Also, There seem to be some peaks at -0.875 Hz and +1.125 Hz in bandpassed signals. So we implemented the notch filters for 0.875 Hz and 1.125 Hz in DEMOD_SIG_I.

After that, we engaged IMMT2 ADSs. They seem to work well. 

[Hirose, Tanaka, Ushiba]

Abstract:

Roll off filters were implemented into TM_OLDAMP_L filter bank of PRs and SRs.
These roll-off filters reduced the noise in PRCL, SRCL, and AS34 signals.

Detail:

In this morning, DRMI was not stable enough to continue the ASC work, so we checked the suspension motions.
Then we found that SRCL signals had no structure above 1 Hz, meaning that SRCL didn't seem to see suspension motions.

To address this issue, we implemented the roloff filters in TM_OLDAMP_L filter for PRs and SRs.
For PRs, we just implemented roll-off filters at 3 Hz while maintaining overall gains at low frequencies.
For SRs, we reduced overall gains to make the loop stable with 3 Hz roll-off filters.

Figure 1 and 2 show the filters we implemented for PRM and SRM, respectively.
Similar filters are also implemented into the other PRs and SRs.
All filters are implemented at FM3 (LOCK) of TM_OLDAMP_L filter bank.

Figure 3 - 6 show the spectra of MICH error, PRCL error, SRCL error, and sideband biuldup signals, respectively.
Black lines show the spectra before this work.
Red lines show the spectra after this work.
Blue lines show the spectra when all TM_OLDAMP_L filters are turned off.
The spectra of PRCL, SRCL, and AS34 signals improved a lot with this work.

Though blue spectra are slightly better than red spectra, we keep TM_OLDAMP_L ON because it takes a long time to calm down if there is no damping controls.
In addition, since the difference in spectra are less than 3 Hz and they do not limit the RMS, these differences should not affect both LSC and ASC.

Then, we implemented the filter in the VIS guardian.
FM3 of TM_OLDAMP_L will be turned on automatically between ALIGNED state and LOCK_ACQUISITION state.

Summary:

After engaging resonant gains in MICH, SRCL, and PRCL, DRMI seems keeping alignment with all ADSs (IMMT2, PRM, BS, SRM).

Detail:

To investigate that we need resonant gains in MICH loop quantitatively, I measured the spectrum of MICH, PRCL, and SRCL error signals with ADS EXCs were on while turning off ADS feedbacks (fig1).
Basic idea is that the peaks appeared in MICH error signals multiplied by the coupling function from MICH to POP90/AS34 should be lower than noise floor of POP90/AS34.

According to the coupling function measured in the original post (MICH to POP90: ~0.008 and MICH to AS34:~0.03), we can obtained the following table.

According from the above tble, it is better to put resonant gains to reduce the offset of alignment signals at least for BS yaw, SRM pitch, SRM yaw, IMMT2 pitch, and IMMT2 yaw.
So, I tested the resonant gains.

Unfortunately, MICH UGF is close to 30 Hz, it is difficult to engage resonant gains at 30.125 Hz and 32.125 Hz.
On the other hands, resonant gains can engaged for the oher ADS frequencies
Figure 2 shows the filter bank of MICH1, and FM4 is the resonant gains I implemented.

For the other LSC loops, resonant gains are also implemented as shown in fig3 and 4 because the UGFs for these loops are higher than that of MICH, and we can engage the resonant gains without any problems.

After that, I tested the ADSs with DRMI 1F lock and DRMI seems stable with all ADSs are ON (fig5).
Also, when engaging the ADSs, POP90 and AS34 signals were increased, so ADSs seem to work well.

Note:

Since the resonnt gains at IMMT2 ADS frequencies cannot be engaged, IMMT2 ADS should have an offset.
So, the current lignment is still not the best, so it is better to put resonant gains at MICH, PRCL, and SRCL loops by increasing MICH loop UGF if possible.

As reported in klog36998, IMC lock loss sometimes occurred when the ASC feedback signals were reset.

To recover from this situation, I prepared MEDM buttons to insert offsets into the IP PZT actuators temporarily.

When the "Insert" button is pressed, the offset is set to match the PZT input signal from 30 seconds before. If the calculated offset is outside the range from 0 to 150, the offset is not inserted.

When the "Return" button is pressed, the inserted offsets can also be gradually returned to 75V. (FIG1)

CAUTION: These buttons have not been fully tested yet. Please do not use these MEDM buttons until the test is completed.

with takafumi.ushiba, takaaki.yokozawa, hirose.chiaki

Summary

We checked the effect of the SRCL resonant-gain (resG) filters at the ADS frequencies and measured the coupling from the LSC length error signals to AS RF34 and POP RF90. The SRCL resG filters suppressed the injected peaks in the RF signals. For MICH, no resG filter is currently used.

Measurement

The interferometer was brought to ALIGNING_DRMI. The IMMT2 and PRM ADS loops were kept on, while the BS and SRM ADS loops and the SRM BPC loop were off. The BS/SRM ADS CLK_GAINs were set to zero to avoid angular excitation from the ADS itself.

For the SRCL measurements, longitudinal excitation was applied to the SRM TM TEST L at 22.125 Hz and 24.125 Hz. For the MICH measurements, longitudinal excitation was applied to the BS TM TEST L at 14.125 Hz and 16.125 Hz.

Date directory: /users/Commissioning/data/DRMI/2026/0824

SRCL resG check

At both 22.125 Hz and 24.125 Hz, the excitation peaks seen in AS RF34 and POP RF90 were strongly suppressed when the SRCL resG filter was enabled.

Figures: SRCL_22p125.png, SRCL_24p125.png

Length-signal spectra: SRCL_peak_22p125.png, SRCL_peak_24p125.png

MICH measurement

MICH currently has no resG filter at these ADS frequencies, so the spectra were measured without resG. Clear excitation peaks were observed in the MICH length signal and in the RF signals.

Figures: MICH_14p125.png, MICH_16p125.png

Length-signal spectra: MICH_peak_14p125.png, MICH_peak_16p125.png

L-to-AS34/POP90 coupling

Using the measured LSC length-error amplitude and the corresponding RF peak amplitude, we estimated the conversion from the measured MICH/SRCL length error to AS RF34 and POP RF90.

These measurements will be used for evaluating how longitudinal motion excited by ADS can couple back into the angular control signals.

[Yasui, Nakagaki]

We installed LAN cabling for CC-10 reading.

#1: IXC (inside clean room) – KEK booth
#2: IYC (inside clean room) – IYA (inside clean room) 

With Yokozawa-san

Initial alignment for Xarm, Yarm, PRMI, SRM were performed.

With Kenta Tanaka, Hiroki Fujimoto, Takaaki Yokozawa

Summary

We investigated the BS and SRM ADS during the DRMI 1F LOCK. Adjusting the relative ADS gains showed that increasing the BS gain caused oscillation, while reducing the SRM gain stabilized the BS motion. However, an offset remained in the SRM ADS Y error signal and caused continued drift. With only the BS ADS engaged, the DRMI could be locked relatively stably.

Details

• We tested the relative ADS gains of BS and SRM. (fig_001.png)
  • Increasing the BS gain caused oscillation.
  • We then reduced the SRM gain relative to BS.
  • With (BS PIT, BS YAW, SRM PIT, SRM YAW) = (0.3, -0.3, -10, -30), the BS motion became stable.
  • However, an offset was visible in the SRM ADS error signal in YAW, and the SRM continued to drift.
• We then engaged the ADS only for BS.
  • The BS ADS error stayed around zero, and the DRMI was comparatively stable.
  • Even after the DRMI lock was temporarily lost and re-locked, BS returned to approximately the same alignment.
  • After the re-locking, the DRMI remained locked for about 8 minutes.
  • IMMT2, PRM, and BS alignment values could be recorded before the lock loss.
• ASC_LOCK.py was updated so that ENGAGE_ADS_FOR_DRMI.main() sets the SRM ADS oscillator clock gains to 300:
  • ADS-PIT_SRM_OSC_CLKGAIN = 300
  • ADS-YAW_SRM_OSC_CLKGAIN = 300

with Yokozawa-san

Since this morning, the interferometer could not reach DRMI_1F_LOCKED for several hours.

We first performed the initial alignment for XARM, YARM, OMC, PRMI, and SRY. Although the RF90 signal was improved after adjusting PRM, the DRMI still could not lock.

After further investigation, we found that some resG filters remained ON in the LSC filter banks even after going to DOWN. This prevented the DRMI from locking properly.

After turning off the resG filters in the MICH and PRCL loops, the DRMI could lock again.

To avoid the same issue, we modified the VERTEX Guardian so that the following filters are turned OFF in the DOWN state:

• MICH1 FM2 (resG_test)
• PRCL1 FM6 (resG_test)

SRCL1 FM4 (resG_22-24) was already configured to be turned OFF in DOWN.

The DRMI lock was recovered, although the lock stability still needs further improvement.

Fujimoto, Hirose, Tanaka

## SRM ADS

SRM ADS also improved AS34. It seems to be reproducible yesterday's setting (fig.1). We implemented it to the ASC_LOCK guardian

## BS ADS trial

### change dither frquency

#### from 22.125 Hz (PIT) and 24.125 Hz (YAW) to 36.125 Hz (PIT) and 38.125 Hz (YAW)

BS oplev seems to have a peak at 24 Hz even though we don't inject any excitaion to BS (fig.2). So we decided to change the dither frequencies. We looked into the frquency region. There are no peaks both in POP90 and in AS34 above 35 Hz. We changed the dither frequencies from 22.125 Hz (PIT) and 24.125 Hz (YAW) to 36.125 Hz (PIT) and 38.125 Hz (YAW). We used the ADS-{PIT,YAW}_{TMSX, TMSY}_DEMOD_SIG_OUT channels as AS34 and ASDC signals. We measured the demod. phases by POP90 (fig.3), AS34(fig.4), and ASDC(fig.5) several times. And we remeasure the deomod. phases every lock restorements. As for ASDC, AS34, there seem to be low coherence about BS alignments even though peaks are observed in ASDC or AS34.  On the other hands, in POP90, there are some coherences. However, YAW phasing seems to be no reproducibility. Therefore, there seems to be other coupling, for example, L to Y. 

Unfortunately, Since MICH Lenght control UGF is close to these dither frequencies, we could not engage resG filters. We considered that L2Y coupling can be decreased by changing the rotation center of BS but this adjustment depends on the beam position on BS and the position is changed by the alignements of DRMI. Therefore, we changed the dither frequencies again to lower frequencies and tried to decrease the L2Y coupling by implementing resG filters in MICH loop. 

### from 36.125 Hz (PIT) and 38.125 Hz (YAW) to 16.125 Hz (PIT) and 14.125 Hz (YAW)

We looked into the frequency region again. Then, around 14 Hz, 16 Hz, and 18 Hz, there seems to be no peaks. So we tried to implement YAW and PIT ADSs with 14.125 Hz and 16.125 Hz, respectively. We confirmed the reprocibility of phasing if we use the resG filters in MICH filters. I tried to engage the BS ADS but PO90 decreased (fig.6). Also, SRM seems to move the opposite direction when BS ADS was engaged 

Following Fujimoto-san's result in klog:37384, the FSR index assignment was changed to a method based on the frequency differences between the measured resonance peaks. With this revised method, the deviations from the design values became 3.01(18) cm for SRX and 2.385(42) cm for SRY. Compared with the results of klog:37250 and klog:37260, namely 2.80(13) cm for SRX and 1.757(50) cm for SRY, the SRX result is considered consistent, while the SRY result is closer than the previous value reported in klog:37381 but still shows a small discrepancy. Using the same procedure as in klog:37381, the SRC length and Schnupp asymmetry derived from SRC were also calculated, yielding 66.61828(92) m and 3.33605(185) m, respectively. Compared with the klog:37260 results of 66.61409(70) m for SRC and 3.34023(139) m for the Schnupp asymmetry derived from SRC, the agreement improved relative to klog:37381, although small differences remain. Furthermore, the beat frequency closest to 0 Hz, as obtained from the fitting results, was found to be approximately four times larger than that obtained in klog:37250 and klog:37260. Since this value should ideally be 0 Hz, the larger offset observed here is unexpected, and its cause is currently unknown.
 

• Following Fujimoto-san's result in klog:37384, the FSR index assignment was revised. The peak near −1.6 GHz was assigned an FSR index of 0, and the frequency difference between adjacent peaks was divided by the design FSR. The resulting values were rounded to the nearest integer to assign the FSR indices. The measured frequencies were then fitted with AN+B where A and B are fitting parameters and N is the FSR index. The fitting results are as follows.

  SRX (Fig. 1)
  A: 2.195115(57) MHz
  B: −1603.604(57) MHz

  SRY (Fig. 2)
  A: 2.307862(15) MHz
  B: −1600.5506(94) MHz

  Since A corresponds to the FSR, the cavity lengths become:

  SRX
  Fitted length: 68.2863(18) m
  Design length: 68.2562 m
  Difference (fitted − design): 3.01(18) cm

  SRY
  Fitted length: 64.95025(42) m
  Design length: 64.9264 m
  Difference (fitted − design): 2.385(42) cm

  Compared with the klog:37250 and klog:37260 results of 2.80(13) cm for SRX and 1.757(50) cm for SRY, the SRX result is considered consistent. The SRY result is closer than the value reported in klog:37381, although a small discrepancy remains.
   

• Using these results, the SRC length and Schnupp asymmetry were calculated following the same procedure as in klog:37381.

  SRC
  Calculated length: 66.61828(92) m
  Design length: 66.5913 m
  Difference (calculated − design): 2.698(92) cm

  Schnupp asymmetry
  Value derived from SRC: 3.33605(185) m
  Design value: 3.3298 m
  Difference (derived − design): 0.625(185) cm

  Compared with the klog:37260 results of 66.61409(70) m for SRC and 3.34023(139) m for the Schnupp asymmetry derived from SRC, these values are closer than those reported in klog:37381, although small differences remain.
   

• In addition, in the previous fitting (klog:37381), adding +1 to the FSR indices of the two positive-frequency peaks, or subtracting 1 from the FSR indices of the two negative-frequency peaks, reproduces the same results obtained here. This indicates that the FSR indices of two resonance peaks had been assigned incorrectly for both SRX and SRY in the previous analysis.
   

• Following this revision, the analyses in klog:37250 and klog:37260 were also rechecked. No changes were found in any of those measurement results, indicating that the FSR indices used in klog:37250 and klog:37260 had been assigned correctly.
   

• Finally, the beat frequency closest to 0 Hz was calculated from the fitting results for both the present analysis and the results of klog:37250 and klog:37260, yielding the following values.

  Present results
  SRX:1.025065 MHz
  SRY:1.105628 MHz

  klog:37250 and klog:37260
  SRX:0.25572 MHz
  SRY:0.24769 MHz
  PRX:−0.034825 MHz
  PRY:−0.042492 MHz

  Ideally, these beat frequencies should be 0 Hz, but the offsets in the present measurements are substantially larger. The reason for this discrepancy remains unknown.
   

This is additional information related to klog37380.

• REFL QPDA1 RF17

Figure 1 shows the power spectra of REFL QPDA1 RF17. No excitation was applied in this measurement. I compared the QPD signals before phasing (0 deg) and after phasing (+75 deg). In both cases, the QPD signals show correlation with the PR3 OPLEV signals, and no clear change was observed after phasing. (FIG1)

• AS QPDA2 RF28

I also checked the power spectra of AS QPDA2 RF28 and the transfer functions between the QPD and OPLEV signals. I compared three demodulation phases: [-46.6 deg, 0deg, +46.6deg]. The transfer functions were measured when BS was excited and when SR3 was excited. (Figure 2 shows the results with BS excitation, and Figure 3 shows the results with SR3 excitation.)
The demodulation phase plots in klog37368 were made by plotting the I and Q signals before phasing as the real and imaginary parts, respectively.
Based on these plots, I estimated how the signal should change when the demodulation phase is rotated. The table below compares this expectation with the results obtained after actually changing the demodulation phase.

・I also plotted the BS and SR3 signals measured before phasing. The two results show a relatively large difference, so it is not clear whether the measurement has good reproducibility (FIG4).

・Changing the demodulation phase corresponds to rotating the real and imaginary axes. Therefore, the I-phase and Q-phase signals after phasing should be the projections of each degree-of-freedom signal onto the rotated axes. However, from the current results, it is not clear whether the signals measured at +45 deg and -45 deg are consistent with the projections expected from the signals before phasing. Therefore, the difference between the expected and measured values may not be explained only by the demodulation phase rotation. The reproducibility of the measurement should also be checked.

・Since I am not sure whether the demodulation phase plots are reproducible, I think we should reduce the coupling independently of the demodulation phase, for example by using multiple QPDs to cancel the coupling from other degrees of freedom, or by making the ASC of the other degrees of freedom more robust.

Note 

I will upload photos of the parts that were changed for MICH ASC this time.(FIG5, FIG6, FIG7)