I checked the IM transfer functions in vacuum. The DC gain of all transfer functions was decreased by 3~5dB. The position change of the OSEMs was 200um maximum (H3 and V1). The measurement for the V1 failed. 

The log and fig made by Yu-san.

I checked the GAS transfer functions in vacuum. They were consistent with the references.

I checked the TM transfer functions in vacuum. They were consistent with the references.

I forgot to attach fig9 in the original post.
See attached figure.

[Kimura and Yasui]

 We have updated the Q-mass for IXC and the measurement PC on 2026/4/16.
We connected five Q-mass units to a single laptop and began continuous measurement of residual gas inside the BS,
IXC, IYC, EXC, and EYC chambers.
Five measurement graphs are attached. The horizontal axis represents time, and the vertical axis represents pressure (Pa).

[Kimura, Yasui and H. Sawada]
This document records the vacuum evacuation of the SRM and the opening of the gate valve between the SRM and SR2.
[SRM Vacuum Evacuation] 
Vacuum pressure inside the SRM and valve operations
2026/4/14
13:09       9. 8 x 10^4 Pa
13:12       Dry Pump Turned ON, Angle valve opening: 270 degrees
13:23       9.6 x 10^4 Pa
13:31       9.6 x 10^4 Pa -----> Angle valve opening: 90 degrees + 360 degrees
13:40       7.8 x 10^4 Pa
13:50       5.0 x 10^4 Pa
14:00       2.9 x 10^4 Pa
14:11       1.5 x 10^4 Pa
14:13       9.3 x 10^3 Pa
14:20       Angle valve opening: Fully open
14:30       4.5 x 10^3 Pa
14:40       2.3 x 10^3 Pa
14:50       1.3 x 10^3 Pa
15:00       6.8 x 10^2 Pa
15:10       4.1 x 10^2 Pa
15:20       2.7 x 10^2 Pa
15:30       1.9 x 10^2 Pa
15:50       1.1 x 10^2 Pa
16:00       8.8 x 10^1 Pa
16:10       7.5 x 10^1 Pa
 

2026/4/15
9:35       1.9 Pa [OMMT 1.1 Pa]
9:32?      GVommt Open ---> 2.1 Pa [OMMT 7.1 x 10^-1 Pa]
9:44        TMP Turned ON
9:54        9.4 x 10^-3 Pa [TMP in Normal Operation]
10:15       1.8 x 10^-3 Pa
10:32       1.3 x 10^-3 Pa
10:50       1.1 x 10^-3 Pa
11:13       9.7 x 10^-4 Pa
12:11       7.8 x 10^-4 Pa

2026/4/16
16:00       GVsrm Open

[About ion pump operation] 
  Approximately 2:50 PM, we turned on the ion pump power to activate the ion pump, at which point the SRM pressure rose to the 10^-3 Pa range.
We waited until 3:30 PM for the pressure to begin declining, but since it did not, I turned off the ion pump power.
The SRM pressure returned to the 10^-4 Pa range.
 Although this is a qualitative explanation, ion pumps near the cryostat tend to have higher outgassing rates compared to those near the ambient-temperature vacuum chamber.
Since the cryostat’s low-temperature pumping effect is orders of magnitude greater, we speculate that the amount of gas adsorbed by the internal getter in the ion pump near the cryostat is smaller.
 In contrast, we estimate that it takes 5 to 6 hours to activate the ion pump near the ambient-temperature chamber.
 
 

[Tanaka,Chen,Yu,Saito]

We fitted the beam profile measured after the first lens in klog:36752. The deviations of the fitted values from the calculated values were 0.2% for the waist position and 7% for the waist size. Next, we measured and fitted the beam profile after the second lens. The deviations from the calculated values were 0.1% for the waist position and 2% for the waist size.
We also measured the absolute frequency of the sub-laser using a wavelength meter.
 

• We fitted the beam profile measured after the first lens in klog:36752 (Fig. 1). The points represent the measured data, and the line represents the fitting result. The green and orange points were used for the fitting, while the blue and red points were not used. The origin corresponds to the position where the laser is emitted. Since the recommended measurement range of the beam profiler is a beam diameter of 45 μm to 4 mm, data points with a beam radius exceeding 2 mm were excluded from the fitting. The calculated values from klog:36739 and the fitting results are as follows:

  Calculated values: waist position = 3008.7 mm, waist size = 0.0112 mm
  Results (average): waist position = 3014.5 mm, waist size = 0.0120 mm

  The deviations of the averaged results from the calculated values were 0.2% for the waist position and 7% for the waist size. Since the errors were small, we proceeded to measure the beam profile after the second lens. First, we placed the beam profiler at the calculated waist position and adjusted it so that the waist size matched the calculated value. Then, we measured and fitted the beam profile after the second lens (Fig. 2). The calculated values from klog:36739 and the fitting results are as follows:

  Calculated values: waist position = 4066 mm, waist size = 0.054 mm
  Results (average): waist position = 4062 mm, waist size = 0.055 mm

  The deviations of the averaged results from the calculated values were 0.1% for the waist position and 2% for the waist size. Since the errors were small, the lens positions were finalized.
   

• To measure the absolute frequency of the sub-laser, we placed a wavelength meter on the transmission side of the beam sampler (Photo 1). The input power to the wavelength meter was adjusted to approximately 1 mW by tuning the HWP before the FI. The laser settings before the measurement were as follows:

  Current: 1.776 A
  Temperature: 24.75 ℃

  The absolute frequency of the sub-laser  was measured while changing the temperature in steps of 0.5 ℃ (Fig. 3). The origin of the vertical axis is 281630 GHz.
  After the measurement, the laser temperature was returned to its original value.

Abstract:

I tested the modal damping of GAS filters on SR3.
The modal damping seems to work wel but yet to be implemented into the guardian.

Detail:

Currently, GAS control of Type-B suspension has a large gain peaking, which is shaking the suspension around several Hz (klog36609).
It might disturb to lock the DRMI stably, I tested the modal damping control of GAS filters by using SR3.

First, I diagonalized the sensor by measuring the response of each LVDT to each resonance.
The data are stored at  /users/VISsvn/TypeB/SR3/Spectrum/2026/0416/.
Procedure is basically same as written in JGW-P1809347-v9 (DC response of actuator is measured by just pushing 5000 cnts from each modal actuator to save the time while it was measured with several tens of mHz transfer function in te document).

Figure 1 and 2 show the decoupled sensor and actuator matrices.
Figure 3 -5 show the suspension plant with modal actuators and sensors, which seems well decoupled.

Then, I designed the control filter and implemented it at FM1 of each modal filter bank.
Figure 6-8 show the measured OLTFs of each modal damping control.

Figure 9 shows the spectrum of IMV OSEM signals with current LOCK_ACQUISITIN state (blue), current OBSERVATION state (pink), and modal damping (brown).
The modal damping has a low noise at high frequency while maintaining the low frequency damping performance.
This control should be implemented into the guardian so that these controls are on at LOCK_ACQUISITION state.

Abstract:

I roughly centered the IR beam on OMMT2 trans QPDs by moving OMMT1.
The alignment doesn't seem to change so much.

Detail:

After GV between SR3 and SRM was opened, I tried to find the IR beam on OMMT2 trans QPDs.
Procedure is as follows.
1. XARM alignment with INITIAL_ALIGNMENT gurdian.
2. YARM alignment wit INITIAL_ALIGNMENT guardian.
3. Change PRM state to MISALIGNED_BF for increasing laser power.
4. Close GRX and GRY shutter.
5. Tweaking OMMT1 angle with coil-magnet actuators to find the beam on OMMT2 trans QPD.
6. Change OSTM state to MISALIGNED_FOR_LOCK_ACQ to avoid unnecessary flash of OMC.
7. Increase laser power for checking if the obtained beam on QPD is really IR beam.

The beam was found and I moved the OMMT1 OPTICALIGN offset for pitch and yaw from -4575 and -1842 to -25000 and -3700 cnts, respectively.
Figure 1 shows the QPD SUM, PIT, YAW, and IMC output.
 The QPD SUM is increasing as IMC output is increasing while pitch and yaw values are kept around zeros.
So, IR beam should be almost center on the OMMT2 trans QPD now.

Since the beam can be found by moving OMMT1 with just coil magnet actuators, the alignment to OMMT1 should not be moved so much.

I'm implementing the IP control with the FLDACCs. I tuned the coefficients for each FLDACC relative to ACC (geophone). Plot 1 shows the spectra of each ACC and FLDACC. Plot 2 shows the spectra of each virtual sensor (L, T, and Y). I measured the transfer functions from each virtual actuator to each virtual sensor (Plots 3, 4, and 5). The gains of the ACCs and FLDACCs are increasing toward DC below 70mHz for L and 50mHz for T.

[Kakei Yu, Kenta Tanaka, Dan Chen]

We measured the temperature dependence of the frequency of the main laser.

The laser beam was picked off in front of the PD used to monitor the laser output power. At this point, the laser power was approximately 57 mW. After inserting an ND filter with a transmission of about 1/200, a wavelength meter(HightFinesse WS-U) was placed for the measurement.

The initial laser settings before the measurement were:

• Current: 1.550 A
• Temperature: 41.85 °C

The laser frequency was measured while varying the temperature (results will be reported later).

After the measurement, the laser temperature was returned to the initial value. We then confirmed that PLLX, PLLY, PMC, and IMC were all successfully locked.

[Tanaka,Hirose,Saito]

Based on the optical layout plan in klog:36739, we installed mirrors, lenses, and a beam splitter.
To achieve mode matching, we measured the beam profile after the first lens.
In addition, two irises were installed to align the optical path of the sub-laser beam with IR laser on the POS table.
 

• Following klog:36746, we installed mirrors and lenses (Photo 1). We completed the installation of optical components required for mode matching and alignment of the sub-laser.
   
• To fine-tune the position of the first lens and match the waist after the first lens to the calculated result (klog:36739), we first placed a beam profiler at the calculated waist position and adjusted the setup so that the waist size matched the calculated value. Then, we measured the beam profile after the first lens. The fitting will be performed later.
   
• To align the optical path of the sub-laser beam with IR laser on the POS table, we installed two irises. The first iris was placed immediately after the first lens that the IR beam passes through after passing through the periscope on the POS table. The second iris was placed in front of the mirror used during the beam profile measurement. We plan to perform alignment so that the sub-laser beam passes through the irises, using the mirrors and beam splitter installed after the lenses for mode matching.

We connected two vacuum gauges and a GV controller to the OMMT-GV automatic closure device and confirmed that it is operating normally.

Monitoring is currently off (yellow light).

We will configure the operating thresholds and start monitoring at a later time.

[Takahashi, Ushiba]

Abstract:

We discussed how to unify the control schemes for the inertial damping of Type-A and Type-B suspensions.
Basically, we agreed that the inertial damping control scheme should align with the current Type-A control scheme.
One change to the Type-A control filter is increasing the pole frequency from 0.1 mHz to 0.5 mHz pole to convert acceleration and velocity to displacement.
This modification reduces the large transient signals while keeping small phase rotation above 30 mHz.

Detail:

Since SRM is not used for a long time, control strategy of SRM is completely different from the other susensions, so we started to unify the control strategy so that we can easily understand it.
For the first step, we discussed the control scheme of inertial damping controls.

Currently, each filter related to the inertial damping control is used for the following concept.
ACCINF: Calibrate raw geophone signals into velocity signals with 3-mHz second-order high pass filter.
FLDACCINF: Calibrate FLDACC local feedback signals into veocity signals with 0.1 mHz pole and 10 mHz second-order high pass filters.
ACCBLEND: Calibrate velocity signals from geophone and FLDACC into displacement with 0.1 mHz pole. Setting crossover frequency between geophone and FLDACC at 100 mHz including phase compensation and inter-calibration.

On the other hands, SRM filters are designed as follows.
ACCINF: Calibrate raw geophone signals into displacement signals.
FLDACCINF: Calibrate FLDACC local feedback signals into displacement signals.
ACCBLEND: only inter-calibration.

If we use SRM-type filter setting, we have no chance to measure the acceleration/velocity signals at DQ channels, which is very incomvenient for the suspension health check.
So, we decided to use control scheme used for Type-A suspensions as a default concept.

In addition, we slightly moodified the filter setting for Type-A suspensions; changing pole frequency from 0.1 mHz to 0.5 mHz, which is used for converting acceleration to velocity or velocity to displacement.
Owing to this modification, transient signals when starting suspension operation becomes small while maintaining the phase rotation at 30/50 mHz sufficiently small.

After the modification of the filter, I checked if the inertial damping control can be stably engaged or not.
Figure 1 shows the comarison between the spectra before (blue) and after (red) changing pole frequency.
Though I have no idea why the spectra around 0.25 Hz and at high frequency are significantly reduced in red, no significant degradation can be seen, so the modification itself should be fine.

[Tanaka,Saito]

Based on the optical layout plan in klog:36739, we installed a newly purchased FI, a beam sampler, and mirrors. The transmission of the FI reached approximately 85%.

• We replaced the contaminated FI reported in klog:36739 with a newly purchased one (Photo 1). This FI has an aperture of 3 mm. Since the laser beam radius at the planned position in the optical layout is about 1.2 mm, we placed the HWP, PBS, and mirrors upstream of the FI as close together as possible, reducing the beam radius at the FI position to approximately 0.8 mm. After alignment, the input power was about 154 mW and the output power was about 131 mW, corresponding to a transmission of approximately 85%. A beam sampler with a reflection-to-transmission ratio of 9:1 was installed after the FI. Six mirrors were placed on the reflection side of the beam sampler.

Unfortunately, since the right-side wall shown in Photo 1 cannot be removed, it is difficult to install an additional mirror and perform alignment.

I checked the geophone performance by FLDACC status. Plot 1 shows the spectra of the geophones in the SAFE state, where the FLDACCs were not locked but were free-running under DC actuation to the proof mass. Plot 2 shows the spectra of the geophones in the READY state, where the FLDACCs were locked in ~20Hz UGF. In this case, the geophone spectra have been smeared by the FLDACC's activity.

[Kimura, Yasui and M. Takahashi]

 The duct shield cryocoolers (Yea, Yer) and the cooling water circulation system at Y-end were shut down at 9:00 a.m. to perform repairs on the Y-end feedwater pump.
Since the repairs on the feedwater pump were completed, the duct shield cryocoolers (Yea, Yer) and the cooling water circulation system were restarted at 1:30 p.m.

While the cooling water circulation system was shut down, the SLACK alarm was temporarily disabled.