Reports of 29202
MIF (General)
takafumi.ushiba - 13:04 Wednesday 13 November 2024 (31612) Print this report
Comment to Increasing the power on CARM out-of-loop PD and measuring CARM sensing noise (31601)

Komori-kun,

Did you change the whitening filter setting of PRD1 during this measurement?
Whitening filter of PDA1 was turned off after locking PRFPMI to avoid saturation during the lock acquisition.
So, if you did not change the whitening filter setting of PDA1, it might be limited by ADC noise.

Also, CARM IN1 gain during the OBSERVATION state is small, so sensing noise might be limited by not PDA1 noise itself but input noise of CMS.
So, it is better to also check the spectrum of K1:LSC-CARM_SERVO_MIXER_DAQ_OUT_DQ to confirm CMS input noise doesn't contaminate the signals.

FCL (Air)
shinji.miyoki - 11:52 Wednesday 13 November 2024 (31611) Print this report
Temp recovery at corner station

Because of miscommunication, the FFUs at SRM and SR3 were not operated for the OMC venting although the SR-C Daikin cooler was operated. Then the temp in the Corner station decreased by ~ 0.5C. I asked Hayakawa-kun to turn on all FFUs at SRM/SR3 around 9:30 to recover the temp.

In addition, I set 4 Sunrise heaters (near BS, SR2, PR3)at Level 3 from 12:00 to accelerate the temp recovery.

Images attached to this report
MIF (General)
takaaki.yokozawa - 11:11 Wednesday 13 November 2024 (31610) Print this report
Initial alignment 241113
I performed the initial alignment (XARM, YARM, PRMI) and performed the alignment for OMC (OMMT2 QPD centering, OMC QPD centering and record the actuator values for OMMT1, OMMT2 and OSTM).
Now we can use the X arm or Y arm with better alignment.
MIF (General)
kentaro.komori - 7:19 Wednesday 13 November 2024 (31601) Print this report
Increasing the power on CARM out-of-loop PD and measuring CARM sensing noise

[Tanaka, Komori]

Abstract:

We increased the laser power on REFL PDA 3 for out-of-loop CARM sensing and PDA 4 for MICH sensing, and measured the CARM sensing noise.
Our findings indicate that the frequency noise stabilized by the interferometer is not limited by the CARM shot noise below several hundred Hz, which we should address in the near future.

Detail:

The triger of this work is taking a look at the spectra of CARM in-loop (PDA 1) and out-of-loop (PDA 3) signals at 00:00 UTC on Nov. 11th and observing that the out-of-loop PD signal was too small to effectively monitor the frequency noise (Fig. 1, blue), where the laser power on PDA 3 was six times lower than on PDA 1.

Then, we came up with increasing the power on REFL PDs to improve the measurement of the CARM sensing noise, and we did that by adjusting the HWP before PDA 3/4.
The current power levels on PDA 1, 3, and 4 with a 1.3 W input under the PRM-aligned, others-misaligned state are 33 mW (unchanged), 24 mW, and 44 mW, respectively.

Please do not increase the IMC output power at this moment.
Kenta will reset the HWP angle later this week.

With the increased power, we measured the CARM error signals from PDA 1 and PDA 3 with the PRM aligned and other optics misaligned.
As described in the klog:29386, the measured spectra provide the CARM sensing noise, including both the CARM shot noise and the residual amplitude noise.

The results are shown in the upper left panel of Fig. 2 (red and blue lines), along with references to two dark noise spectra (brown and black).
The blue spectrum reveals several structures with significant coherence with the IMMT1_TRANS_QPD signal (bottom right), indicating that better centering on PDA 3 is needed in the future.
The red spectrum also shows an excess compared to higher frequencies (likely limited by shot noise), although it has low coherence with other signals (upper right panel), suggesting that the excess noise is due to amplitude modulation imposed by the IMC.

Some prominent peaks in the DARM spectrum, such as at 116 Hz and 350 Hz, are already present in this excess.
We will evaluate whether this excess noise contributes to the current DARM sensitivity and to what extent it can explain the current sensitivity.

Images attached to this report
Comments to this report:
takafumi.ushiba - 13:04 Wednesday 13 November 2024 (31612) Print this report

Komori-kun,

Did you change the whitening filter setting of PRD1 during this measurement?
Whitening filter of PDA1 was turned off after locking PRFPMI to avoid saturation during the lock acquisition.
So, if you did not change the whitening filter setting of PDA1, it might be limited by ADC noise.

Also, CARM IN1 gain during the OBSERVATION state is small, so sensing noise might be limited by not PDA1 noise itself but input noise of CMS.
So, it is better to also check the spectrum of K1:LSC-CARM_SERVO_MIXER_DAQ_OUT_DQ to confirm CMS input noise doesn't contaminate the signals.

VAC (General)
takahiro.yamamoto - 3:21 Wednesday 13 November 2024 (31608) Print this report
Preparation of DAQ for the gate valve readout

Abstract

EPICS gateway for the vacuum network was prepared.
It's available as /kagra/apps/epics-deb12/extensions/bin/linux-x86_64/gateway from Debian12 system.
It was also confirmed that vacuum-related channels that do not follow the DAQ definition due to technical issues can be obtained using the alias function.
We can start taking data by DAQ soon after VAC group decides a channel name for KAGRA DAQ system for each readout value.
 

Details

In vacuum network, some EPICS IOCs were installed for reading CC-10 readout and gate valve status. Because of the problem on a number of IP address, it's difficult to assign IP address for each IOC. So we decided to use one EPICS gateway for the vacuum network and only EPICS gateway would have an IP address for DGS network.

Built EPICS gateway for Gentoo and Debian10 system already exists in /opt/rtapps and /kagra/apps, respectively. But constructing EPICS gateway server as Gentoo system is not so good from the view point of maintainability and Debian10 system is already expired in the KAGRA system. So I newly built the EPICS gateway for the Debian12 system in /kagra/apps/epics-deb12 (it should also work well on RL9 system).

Because of the technical problem, EPICS channels in vacuum network are named as KGRVAC:FOO_BAR:BAZ. Though these channels can be seen on EPICS native tools such as MEDM, StripTool, etc., naming convention doesn't follow one on KAGRA DAQ system. We decided to solve this issue by using the ALIAS function on the EPICS gateway server. The ALIAS function can be used by setting by PV list file as follows.
----------
K1:HOGE-FUGA_PIYO ALIAS KGRVAC:FOO_BAR:BAZ
----------

The first and third column is alias name for DAQ and original name in vacuum network, respectively.

Fig.1 shows the test result of ALIAS function and it works well. Because the test server is not in vacuum network, I used K1:VAC-PRESSURE_CS_SRM as original channels instead of KGRVAC:... and alias name is set as X1:... in order to avoid any conflict.

Construction Memo
On Debian12 system, the version of libreadline is different from Gentoo and Debian10 system. So binary file for Gentoo and Debian10 cannot be executed on Debian12 system. In fact, creating libreadline.so.6 as an alias to libreadline.so.8 allowed to use old binary on Debian12 system. But it's not so good manner, so I newly built.

Building EPICS base and gateway with gcc v12 which is available on Debian12 has two compile errors and a code modification was required.
The first problem is related to the difference between ULong and size_t on base/src/libCom/test/epicsExceptionTest.cpp (https://github.com/cms-sw/cmssw/issues/41795).
The 2nd one is related to the scope of class variable (https://github.com/epics-modules/pcas/commit/56403e8e4774dccc3819cab27bc975f48ab5f988).
Both two problems didn't occur on Debian10 (gcc v10) and Debian8 (gcc v4), so it seems to be related to the compatibility between gcc v12 and epics codes.

Images attached to this report
MIF (General)
ryousuke.sugimoto - 2:53 Wednesday 13 November 2024 (31609) Print this report
Linear coupling investigation between geophone and OMC length error (and also DARM)

[Yokozawa, KTanaka, Komori, Sugimoto]

We projected the geophone noise onto the OMC length error signal using the transfer function and noise obtained in the previous measurement (31574). The results are shown in Fig. 1 and Fig. 2. At this time, we used the transfer function obtained with the speaker injection. Note that the coherence is low around 30-70 Hz in the transfer function measurement. It is highly likely that the peaks around 80-200 Hz are due to geophone noise.
We also projected these results onto DARM sensitivity using the transfer function from OMC length error to DARM sensitivity measured in klog31315. The results are shown in Fig. 3 and Fig.4. However, due to the low coherence of the transfer function measurement, it is not clear how reliable this result is.

Images attached to this report
PEM (Center)
tatsuki.washimi - 23:51 Tuesday 12 November 2024 (31606) Print this report
Acoustic injection to OMC area, 2024-11-11

Yokozawa-san performed a broadband acoustic injection for the OMC area, from 2024-11-11 02:04:00 UTC, with DAC output = 10,000 count.

I analyzed this data same as klog31293.

  • reference data: 128s from 2024-11-11 02:01:00 UTC
  • injection data: 128s from 2024-11-11 02:04:00 UTC

These results are attached:

  • Fig.1: spectrograms and ASDs around this time
  • Fig. 2: ASDs and Coherences with MIC, for each channel, ref and inj
  • Fig. 3: CF and Projection of MIC -> Geophone
  • Fig. 4: CF and Projection of MIC -> OMC error
  • Fig. 5: CF and Projection of Geophone -> OMC error
  • Fig. 6: ASDs and Coherences with MIC, for (OMC error)^2, ref and inj
  • Fig.7: Zooming up of Fig.6, at 80-200Hz
  • Fig.8: Coherence between the OMC trans PD and the OMC error (linear, squared)
  • Fig. 9: TF amplitude of OMC error -> OMC trans PD
  • Fig. 10: TF amplitude of (OMC error)^2 -> OMC trans PD
  • Fig. 11: Projection of the OMC error (linear, squared) -> the OMC trans PD
  • Fig. 12: Comparison between Oct.12 and Nov.11
Images attached to this report
MIF (General)
kenta.tanaka - 23:49 Tuesday 12 November 2024 (31604) Print this report
Phasing for in/out loop sensors for CARM

Komori, Tanaka

As posted by Komori-san (Komori-san will post the log later), PDA3 response about CARM seems to be difference from PDA1 one. So Ushiba-san already performed the phasing for PDA3 (klog31410) but we confirmed whether the phasing for PDA3 got bad or not. The green and brown line in Fig. 1 shows I and Q signal when Xarm locked and IMC excited with the CARM_SERVO_EXC_A_CALI channel at 1023 Hz.As you can see, the phasing seemed to be almost fine. We just adjusted the phase slightly to the peak in Q-phase was eliminated completely.

Then, we confirmed PDA1 phasing. PDA1 seems not to be performed the phasing. So we performed the phasing for PDA1 (fig.2).

After all of the measurements including to Komori-san's posted ones, we found that PDA1 is used for the DGCARM control. So we restored the demod. phase and the setting of whitening filters to the previous one.

Images attached to this report
MIF (General)
ryousuke.sugimoto - 23:35 Tuesday 12 November 2024 (31607) Print this report
Comment to TF measurement between the geophone and OMC length error (31574)

I also compared the measured geophone noise with the previous result obtained before the OMC stack was connected.
There were improvements in areas such as around 30-40 Hz and 75- 100 Hz. However, it also worsened in many regions.
Above about 280Hz, it was limited by the sensing noise.

Images attached to this comment
MIF (General)
ryousuke.sugimoto - 23:28 Tuesday 12 November 2024 (31605) Print this report
Comment to TF measurement between the geophone and OMC length error (31574)

I compared the transfer functions from the geophone to the OMC length error between those obtained using speaker injection and shaker injection.
Fig 1 shows the overall, and Fig 2 shows a zoomed view of 50–300 Hz, where coherence is observed (speaker: red, shaker: blue). While the results were mostly consistent, slight differences may provide insights into the noise path.

Images attached to this comment
DetChar (General)
Takahiro S. Yamamoto - 20:32 Tuesday 12 November 2024 (31603) Print this report
Comment to Violin modes moving (31594)
# Summary
(only violin modes within 160-200Hz)
I show the figures that the shift in the peak frequency (Fig1) and the change in the fitted width(Fig2) with respect to Oct15. Peak frequency is systematically shifted toward higher frequency. Width seems not be systematically changed.

Fig3 shows the estimated width. Some points indicate exact zero. These correspond to the peaks that are not identified by the monitoring tool (see below) but can be identified by the human eye.

# identification and ASD fitting

- Peaks in ASD are found by line monitor tool that is being implemented by Takahiro S Yamamoto and Hirotaka Yuzurihara.
- The tool generate ASD by using 86400sec data, tsft=1800sec, toverlap=900sec, window=hann. Also, the normalized periodograms are generated and used to identify the artificial lines.
- Line monitor tool can give a curve fit by the violin function and a Gaussian function. The violin function is defined by

$$ G_\mathrm{violin}(f; f_\mathrm{loc}, w, A) = \frac{A f_\mathrm{loc}^2 w^2}{(f^2 - f_\mathrm{loc}^2)^2 + w^2 f^2} $$

where $f_\mathrm{loc}$ is the peak frequency, $A$ is the amplitude and $w$ is the full-width-half-maximum (FWHM). The tool fit ASD by using `scipy.optimize.curve_fit`. The peak frequency is fixed, and $A$ and $w$ are optimized. The fitting range is crucial for the fitting. We start from the range of $[f_\mathrm{loc} - 2/1800(=0.0011\cdots)\mathrm{Hz}, f_\mathrm{loc} + 2/1800 \mathrm{Hz}]$. If the optimized $w$ is wider than the fitting range, we extend the fitting range by twice. We repeat this process and stop the loop when the optimized $w$ is narrower than the fitting range or the fitting range reaches 0.1Hz.

# not done
- The fitting range is not optimized by the statistics.
- The global fitting, which is carried out in the O3GK noise budget paper, is not done.
- Error bar is missing.

Images attached to this comment
VAC (OMC)
takashi.uchiyama - 16:48 Tuesday 12 November 2024 (31602) Print this report
Venting OMC and OMMT
2024/11/12

Kimura, Yasui, Uchiyama

We vented OMC and OMMT from 9:53 and reached atmospheric pressure at about 12:20.
We opened three flanges of OMC (2-4, 2-6, 2-8).
Images attached to this report
VIS (EY)
ryutaro.takahashi - 14:46 Tuesday 12 November 2024 (31600) Print this report
Comment to Drift of BF GAS (27941)

I changed the setpoint of the heater from 29.0° to 27.0° at 14:32 JST.

DetChar (General)
shoichi.oshino - 12:07 Tuesday 12 November 2024 (31599) Print this report
Comment to Restart Omicron process (31553)
It turns out that the k1sum1 hunged up because the Omicron process, which runs every 15 minutes, is stacking up.
This is because the new segment file creation script outputs the day's segment information every 15 minutes.
After discussion with Yuzuhara-san, it was decided that in the future a new script would be created to cut out segments every 15 minutes from the existing file.

As a first aid, the previously used script to create a segment every 15 minutes was modified to create a segment only for GRD_LOCKED.
MIF (General)
takahiro.yamamoto - 12:03 Tuesday 12 November 2024 (31595) Print this report
Comment to Increasing the laser power (31580)

Is "1.3W without norm" in the legend of Fig.2 a typo of "3.3W without norm" or does this mean current (with norm) UGF is different from one in the past 1.3W situation?
In the former case, it's fine for the calibration. But in the latter case, the front-end calibration is no longer correct.

IOO (OMC)
kenta.tanaka - 11:14 Tuesday 12 November 2024 (31597) Print this report
Comment to OMC DC PDs probably burned (31581)

We added some PD outputs (AS PDA1 RF17/DC, OMC QPD1,2 SUM) around the burned moment in order to look into the power monitor used as the protection trigger (fig.1). At the moment on the left cursor, DARM oscilation could be seen in the inputs of OMC TRANS PDs, then their inputs was satulated soon. After 76 ms, at the moment on the right cursor, AS PDA1 DC output in middle panel of  fig.1 drastically increased to 8 mW. The ususall RMS of AS PDA1 (< ~0.1 mW) seems to be much smaller than this power increasing. so we can use AS PDA1 DC output as the trigger channel.

## Note

OMC QPD SUMs have no fast channels. if fast channels are implemented, OMC QPD SUMs also can be used as the trigger.

Images attached to this comment
DetChar (General)
tomotada.akutsu - 10:45 Tuesday 12 November 2024 (31596) Print this report
Comment to Violin modes moving (31594)

Interesting! The line width has also changed? or maybe only ignorable amount.

DetChar (General)
Takahiro S. Yamamoto - 9:31 Tuesday 12 November 2024 (31594) Print this report
Violin modes moving
I compared the ASDs of Oct15 and Nov7,8. I find the violin modes are moving toward higher frequencies. It would be the effect of cooling the mirror.

Config: Starttime=14:00UTC, Duration=86400sec, tsft=1800sec, toverlap=900sec, window=hann, channel=K1:CAL-CS_PROC_DARM_STRAIN_DBL_DQ, IFOstatus= (K1:GRD-IFO_STATE_N==100) * (no IPC glitch)

Red: Oct15, Blue: Nov7, Green: Nov8

Fig1: 172-192Hz, Fig2: 390-445Hz
Images attached to this report
Comments to this report:
tomotada.akutsu - 10:45 Tuesday 12 November 2024 (31596) Print this report

Interesting! The line width has also changed? or maybe only ignorable amount.

Takahiro S. Yamamoto - 20:32 Tuesday 12 November 2024 (31603) Print this report
# Summary
(only violin modes within 160-200Hz)
I show the figures that the shift in the peak frequency (Fig1) and the change in the fitted width(Fig2) with respect to Oct15. Peak frequency is systematically shifted toward higher frequency. Width seems not be systematically changed.

Fig3 shows the estimated width. Some points indicate exact zero. These correspond to the peaks that are not identified by the monitoring tool (see below) but can be identified by the human eye.

# identification and ASD fitting

- Peaks in ASD are found by line monitor tool that is being implemented by Takahiro S Yamamoto and Hirotaka Yuzurihara.
- The tool generate ASD by using 86400sec data, tsft=1800sec, toverlap=900sec, window=hann. Also, the normalized periodograms are generated and used to identify the artificial lines.
- Line monitor tool can give a curve fit by the violin function and a Gaussian function. The violin function is defined by

$$ G_\mathrm{violin}(f; f_\mathrm{loc}, w, A) = \frac{A f_\mathrm{loc}^2 w^2}{(f^2 - f_\mathrm{loc}^2)^2 + w^2 f^2} $$

where $f_\mathrm{loc}$ is the peak frequency, $A$ is the amplitude and $w$ is the full-width-half-maximum (FWHM). The tool fit ASD by using `scipy.optimize.curve_fit`. The peak frequency is fixed, and $A$ and $w$ are optimized. The fitting range is crucial for the fitting. We start from the range of $[f_\mathrm{loc} - 2/1800(=0.0011\cdots)\mathrm{Hz}, f_\mathrm{loc} + 2/1800 \mathrm{Hz}]$. If the optimized $w$ is wider than the fitting range, we extend the fitting range by twice. We repeat this process and stop the loop when the optimized $w$ is narrower than the fitting range or the fitting range reaches 0.1Hz.

# not done
- The fitting range is not optimized by the statistics.
- The global fitting, which is carried out in the O3GK noise budget paper, is not done.
- Error bar is missing.

Images attached to this comment
DetChar (General)
Takahiro S. Yamamoto - 9:16 Tuesday 12 November 2024 (31593) Print this report
Sideband around lines appear
I compared the ASDs of Oct15 and Nov7,8. In Nov 7,8's ASDs, I found that sidebands are appeared around many lines. I'm not sure the reason of these sidebands. I have not checked the exact locations of the lines and the width of the sidebands. Once the system-b cluster is recovered, I will check them.

Config: Starttime=14:00UTC, Duration=86400sec, tsft=1800sec, toverlap=900sec, window=hann, channel=K1:CAL-CS_PROC_DARM_STRAIN_DBL_DQ, IFOstatus= (K1:GRD-IFO_STATE_N==100) * (no IPC glitch)

Red: Oct15, Blue: Nov7, Green: Nov8,

Fig1: 450Hz-500Hz. You can find lines around 460Hz, 467Hz, 473Hz, 487Hz, 495Hz (I have not checked the exact location of peaks). For Nov7 and 8, these peaks have sidebands while they don't in Oct15.

Fig2: Zoom in a line at 467Hz.

Fig3: You can find similar sidebands on lines in 1020Hz-1080Hz.
Images attached to this report
FCL (Air)
shinji.miyoki - 7:25 Tuesday 12 November 2024 (31592) Print this report
Comment to 3 Heaters stopped at EYC 1F area (31557)

Around 10 a.m., the tripped breaker was recovered, and two sunrise heaters were also recovered at level 2. On the other hand, a new voltage converter (200V—100V) was prepared for one sunrise heater, and it was also operated at level 2.

I changed level 2 to level 3 around 7 p.m. to accelerate the temperature recovery in the EYC 1F area.

For EYV temp adjustment, I tried level 2 (900W) and 3(1.2kW) heating power several times and concluded that level 2.5 is necessary to keep F0 GAS around zero. I will ask the technical staff for 150W heating power by using a small heater prepared in EYV.

Images attached to this comment
MIF (General)
kentaro.komori - 1:38 Tuesday 12 November 2024 (31591) Print this report
Comment to Sensitivity with 5 W input (31584)

When the guardian tried to lock the OMC LSC with the increased power, we encountered difficulties with undesired locking to the TEM00 mode at a power level of only ~5 mW.
This is most likely due to the f1 sideband, as this power level aligns with the current PRM, Schnupp asymmetry, and the sideband frequency of 17 MHz.
To prevent the OMC LSC from locking onto the sideband during high-power operations, we should adjust the threshold accordingly.

DetChar (General)
hirotaka.yuzurihara - 23:03 Monday 11 November 2024 (31590) Print this report
Comment to The time series of the inspiral range and ASD (31586)

This is a supplemental comment.

Initially, we investigated the time-variation of the trigger rate computed by Omicron triggers. We found the trigger clusters periodically appeared and disappeared in the band 400 to 2000 Hz in the Omicron trigger plot. Also, we found that the inspiral range has a coincident time variation with the trigger rate. It can be seen on page 2 of slide. Based on the scattered plot, they show a linear correlation.
Further investigation revealed that the ~10% decrease in the inspiral range was due to a worsening in sensitivity around 100 Hz, which Ishikawa-san reported above.

MIF (General)
takafumi.ushiba - 22:44 Monday 11 November 2024 (31589) Print this report
Comment to Sensitivity with 5 W input (31584)

Since current REFL power is not so large and the shot noise would not be small enough for O4b according to the result in klog31577, it might be better to reduce the CMS gain instead of reducing the power on REFL PD.

MIF (General)
ryousuke.sugimoto - 21:45 Monday 11 November 2024 (31588) Print this report
Comment to Sensitivity with 5 W input (31584)

(with Yokozawa-san)

I have noted the procedure for increasing laser power here.
To increase the laser power, we turned the HWP in the PSL room (K1:SYS-HWP_PSL_STEP_DEG) from 14 deg to 26 deg in a 1 deg step. We also adjusted the HWP before the REFL PD (K1:SYS-HWP_IFO_REFL_STEP_DEG) so that the REFL PD would not saturate with each 1 deg rotation of the HWP in PSL (to K1:LSC-REFL_PDA1_DC_OUT_DQ was made not to exceed the threshold value of ~3.56). K1:SYS-HWP_IFO_REFL_STEP_DEG was finally turned from 156 deg to 178 deg.

MIF (General)
kentaro.komori - 20:51 Monday 11 November 2024 (31584) Print this report
Sensitivity with 5 W input

[Tanaka, Sugimoto, Yokozawa, Dan, Yuzurihara, TYamamoto]

Abstract:

We increased the input power to 5 W, resulting in improved sensitivity at higher frequencies.

Detail:

We successfully increased the input power to the IFO up to 5 W, following the same procedure as described in klog:31580.
The detailed procedure will be reported later.
This measurement was conducted just prior to the incident where the PDs were damaged.

The attached figure compares the displacement sensitivity from this measurement with that of the previous month.
Since we changed the gain of LSC_OMC_DC and confirmed that the DARM openloop transfer function did not change, the same calibration factor can be used to estimate the sensitivity.
As expected, the sensitivity improved by a factor proportional to the square root of the power increase, in the frequency range from 500 Hz to several kHz, where the shot noise and PD dark noise were the dominant noise sources.

However, the sensitivity at frequencies in the range of several tens of Hz degraded.
Potential reasons for this degradation include changes in the IFO alignment due to the increased power, as well as changes in coupling from other degrees of freedom, such as pitch, caused by increased radiation pressure.

Images attached to this report
Comments to this report:
ryousuke.sugimoto - 21:45 Monday 11 November 2024 (31588) Print this report

(with Yokozawa-san)

I have noted the procedure for increasing laser power here.
To increase the laser power, we turned the HWP in the PSL room (K1:SYS-HWP_PSL_STEP_DEG) from 14 deg to 26 deg in a 1 deg step. We also adjusted the HWP before the REFL PD (K1:SYS-HWP_IFO_REFL_STEP_DEG) so that the REFL PD would not saturate with each 1 deg rotation of the HWP in PSL (to K1:LSC-REFL_PDA1_DC_OUT_DQ was made not to exceed the threshold value of ~3.56). K1:SYS-HWP_IFO_REFL_STEP_DEG was finally turned from 156 deg to 178 deg.

takafumi.ushiba - 22:44 Monday 11 November 2024 (31589) Print this report

Since current REFL power is not so large and the shot noise would not be small enough for O4b according to the result in klog31577, it might be better to reduce the CMS gain instead of reducing the power on REFL PD.

kentaro.komori - 1:38 Tuesday 12 November 2024 (31591) Print this report

When the guardian tried to lock the OMC LSC with the increased power, we encountered difficulties with undesired locking to the TEM00 mode at a power level of only ~5 mW.
This is most likely due to the f1 sideband, as this power level aligns with the current PRM, Schnupp asymmetry, and the sideband frequency of 17 MHz.
To prevent the OMC LSC from locking onto the sideband during high-power operations, we should adjust the threshold accordingly.

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