[kTanaka, Ushiba]

Conclusion:

Measurement with time span of 64 s (corresponding to a bandwidth of 0.015625 Hz) with the ADS gains increased by a factor of 3 from their nominal values, except for PRM yaw, appears to provide good results for the sensing matrix measurement.

Detail:

We reviewed the sensing matrix measurement results today (klog37289) and found that the coherence was very low for some degrees of freedom (DoFs).

To investigate the cause, we measured the RF PD spectra while exciting the BS with an amplitude of 30000 counts from ISC_INF.
We found large side lobes located approximately 0.05-0.1 Hz away from the excitation frequency.
Since the sensing matrix measurement had a frequency resolution of 0.125 Hz, these side lobes were not sufficiently separated from the excitation lines.

To mitigate the side lobes, we implemented a second-order boost filter in the MICH filter bank, extending the bandwidth from 1 Hz to 0.1 Hz.
However, the situation did not improve significantly.
Therefore, the side lobes do not appear to originate from residual MICH motion.

We then investigated whether the side lobes were caused by angular motion by examining the OpLev signals and the ASC-MICH_{P,Y} signals.
Since the ASC-MICH_{P,Y} signals exhibit peaks around 0.09 Hz, it is likely that the side lobes originate from angular motion.
Furthermore, the coherence between the ASC signals and the OpLev signals is high for SRM, PRM, and IMMT2, all of which are controlled by ADS.
Therefore, we suspected that the ADS control was producing the peak around 0.09 Hz, which in turn generated side lobes in the LSC signals when the BS was excited at 150.125 Hz.

To address this issue, we increased the ADS gains for IMMT2 pitch/yaw, PRM pitch, and SRM pitch/yaw by a factor of 3 in order to increase the ADS UGFs.
Since the PRM yaw loop became oscillatory when its gain was increased by a factor of 3, the PRM yaw ADS gain was left unchanged.

Figure 1 shows the RF PD spectra measured while DRMI was locked and the BS was excited at 150.125 Hz.
The coherence between the MICH and RF PD signals is high, indicating that the measurement quality is improved compared to the previous measurement.
When comparing the new results with the previous measurement, several values changed by significant factors, suggesting that the previous measurement may not be accurate sufficiently.
Therefore, it would be preferable to repeat the sensing matrix measurement.

[Tanaka, Hirose]

This is continued from klog37279.

While locked at DRMI 1f, we measured the sensing matrix for the 3f sensors. 

The sensing matrix is as follows in Table 1. (Values marked with an asterisk (*) have a coherence below 0.85.) We excited the PRM, BS, and SRM of the PRCL, SRCL, and MICH actuators, respectively, at 150.125 Hz. (Figures 1, 2, and 3)

We normalized the results in the table below so that the reference value for the degree of freedom is 1 for each sensor. (Table 2)

Based on the measurement results above(Table 2), we considered the sensor coefficients(Table 4) to achieve the signal response shown in the table below(Table 3).
Table 3 is based on the equations in Fig. 4. 

Table 4 shows the sensor coefficients. The error signal for each degree of freedom is obtained by multiplying each sensor signal by its coefficient and summing the results. These coefficients will be used in the Input Matrix on the MEDM screen.

Table 5 summarizes the calculated coupling of each degree of freedom in the error signals obtained using the sensor coefficients in Table 4. The calculated coupling ratios are close to the ideal values shown in Table 3. 

Next time, we'll insert in this coefficient and try 3f lock.

Replacement of the Shim Plates for the Y_minus Pylon and Rough Measurements in the x and y Directions

Replacement of the Shim Plates

Measurement of the Pylon Height

Rough Measurements in the x and y Directions

Two optical benches (1.8m x 1.2m) were installed in the SK-KAGRA room 2.

The construction of the clean booth will follow at the beginning of August.

I offloaded the BF and F2 GAS filters with the FRs.

Installation of the Y+ Pylon

move and installY+ Pylon

Measurement of the Pylon Height

Hirose, Yokozawa, Saito, Kawakami, Tanaka

We calibrated the 1f signals to nano-meter unit by comparing TFs from actuators to 1f sensors with ones from actuators to LEN OPLEVs. We stopped today's commissioning due to the large earthquakes at Kumamoto, unfortunately.

## What we did

• We tried to calibrate by comparing the response from {SRCL,PRCL] feedback to 1f sensor (K1:LSC-{SRCL,PRCL}1_IN1/K1:LSC-{SRCL,PRCL}2_OUT) with the response from {SRM, PRM} TEST to {SRM, PRM} LEN oplev (K1:VIS-{SRM, PRM}_TM_OLDAMP_IN1_DQ/K1:VIS-{SRM, PRM}_TM_TEST_L_IN2), which was measured in Health check (PRM in klog33132, SRM in klog36856).
  • The measured frequency range of the 1f sensor response (10-100 Hz) differs from the range of the OPLEV response (0.01 - 7 Hz). But above the resonant frequency, which is less than 1 Hz, the frequency response is f^-2. So we estimated the Oplev response value around several tens Hz from the value around several Hz.
    • PRM: Oplev response at 3 Hz = -80 dB, that is, the response at 30 Hz = -120 dB. On the other hands, PRCL 1f sensor response at 30 Hz = -80 dB (green line in right upper panel in fig.1). So we obtained the calibration factor of the 1f sensor,  -120 - (-80) = -40 dB = 0.01 um/cnts. Also, we converted from um to nm, 0.01*1000 = 10 nm/cnts.  The relative phase from oplev to sensor is 180 deg. However, we found that the PRCL -> PRM element in LSC_OUTMTRX is -1. In this case, The actual direction of PRM Longitudinal direction is inverse that the we assumed. So the sign of the input element value should be positive in terms of the "VIS" geometry.
    • SRM: Oplev response at 4 Hz = -101 dB, that is, the response at 40 Hz = -141 dB. On the other hands, SRCL 1f sensor response at 40 Hz = -92 dB (green line in right upper panel in fig.2). So we obtained the calibration factor of the 1f sensor,  -141 - (-92) = -49 dB Also, we converted from um to nm, -49dB + 60dB = 11 dB = 3.5 nm/cnts. The relarive phase is 0 deg. So we applied the sign of the input value to positive.
  • Then, we modified the LOCKING_DRMI_1F state in the VERTEX guardian to input these calibration factors into the LSC INPUT MATRIX.
  • Moreover, we adjusted the each setpoint of MICH, PRCL, and SRCL and the filter gains in FM4 of {MICH, PRCL, SRCL}2  because we changed each unit. 
• After that, we measured the OLTFs and we confirmed the overall gains were not changed (PRCL:fig.1, SRCL:fig.2).
• Then, we tried to measure the sensing matrix of 3f signals but the large earthquake occured at Kumamoto. So we gave up today's commissioning.

## Note

After today's work, I heard the reason why the sign of the value in OUTMTRX from PRCL to PRM is -1 from Yamamoto-san. It is because the definition of the sign of the cavity length change is that the direction which the cavity length expands is postive. So, the positive direction in terms of "LSC" is inverse from the VIS geometry. Therefore, we should change the sign of PRCL, SRCL factors from positive to negative.

[Yokozawa, Hirose]
We performed the initial alignment Xarm, Yarm and DRMI.
And we investigated the coupling to the 3f LSC sensors while the DRMI 1f LSC and ADS loops were both engaged. To avoid the influence of the control loops, we injected a 100 Hz excitation, which is outside the LSC control bandwidth. Both the PRCL (REFL-RF135I) and SRCL (REFL-RF51I) sensors showed strong coupling to the excitation.
However, the PRCL and SRCL excitation signals were visible in REFL-RF135I and REFL-RF51I, respectively, but not in REFL-RF135Q or REFL-RF51Q. Therefore, it appears difficult to separate PRCL and SRCL solely by adjusting the I/Q demodulation phases of the RF135 and RF51 sensors. We plan to perform simulations which sensors show responses to each degree of freedom.
FIG1, FIG2, FIG3: Responses of each sensor when MICH/SRCL/PRCL were excited. (Note: Excitation was performed with the DRMI1f locked.)

Details of the NCal pylon installation

Before starting the installation, we transported the required tools and equipment from the central area to Xend, including a steel ruler, a laser level, slings, and a chain block. We also removed the floor mat in the anteroom of the EXC clean booth and cleaned the floor.

One NCal pylon was moved today. In front of the C-chamber anteroom, the pylon was lifted from its pallet using a tripod and placed on a Bishamon lift table. It was then transported into the anteroom. The protective plastic covering was removed, and both the pylon and the lift table were carefully wiped and cleaned.

Inside the clean area, we moved a workbench that had been located between the anteroom and the installation position. We used some C-clamps, slings, and chain blocks to a beam of the clean booth, and slings and chain blocks were connected to it. The pylon was then moved into the clean booth.

At the installation position, we removed the tape covering the anchor holes and cleaned the area. We also removed the waterproof sheet. We found that there is a boundary or gap in the floor near the installation position, which needs to be considered carefully when adjusting the balance of the pylon.

The pylon was suspended from two directions and moved above the installation position. Shim plates equivalent to those used under the cryocoolers in the cryogenic area were inserted between the floor and the pylon to adjust the inclination.

During this work, we found that the prepared M16 bolts were too long, and therefore the pylon could not be completely fixed to the floor. At present, the pylon is temporarily held by the long bolts and the lifting equipment.

Height and inclination adjustment

The pylon height and inclination were adjusted using a laser level. The reference height was the mark labeled “Cryogenic center,” which was created on August 22, 2017, and reconfirmed on May 3, 2021. We also confirmed that this reference point is approximately consistent with the center of the arm pipe.

This reference point appears to be the one described in klog16644. According to that klog, ETMX was located 8.5 mm below this reference height. However, we have not yet checked whether this relation was modified in later work. For the NCal installation, the important quantity is not simply matching the ETMX height, but accurately determining the relative position between the NCal and ETMX.

A steel ruler was placed on the 640-mm-diameter intermediate positioning plate on top of the pylon. The laser height was measured at four positions corresponding to the (-y), (+x), (+y), and (-x) sides relative to the pylon center.

The final ruler readings today were:

(-y, +x, +y, -x) = (127.5, 127.5, 126.0, 126.0) mm.

Assuming that ETMX is located at the reference height, the nominal design value is approximately 125 mm. However, future fine height adjustment is planned to be performed using shim plates underneath the NCal unit itself rather than underneath the pylon. Therefore, we decided to keep the current readings slightly larger than 125 mm.

Remaining work

• Replace the currently used M16 bolts with shorter bolts. Suitable shorter M16 bolts were found in the central area.
• Replace the current shim plates, whose lateral dimensions are too large, with smaller shim plates. Suitable plates were also prepared in the central area.
• Complete the fixing and alignment of this pylon.
• Install the second pylon on the (+y) side.

The work was not completed today and will continue tomorrow.

Pictures will appear here: link

For the DRMI commissioning, I modified the guardian so that the REFL 3F PD demodulation phases are automatically changed to the optimal values for DRMI 3F lock, as measured in klog37228.
These demodulation phases are currently restored to their default values in the DOWN state so that PRMI can still be locked using the 3F signals.

In addition, I modified the guardian so that the MICH IN1 signal is roughly calibrated in units of nanometers when DRMI is locked using the 1F signals.
To achieve this, the guardian sets the MICH input matrix element to −8.4.
I also changed the gain of FM4 in the MICH2 filter bank from −15 to 1.8 so that the OLTF of the MICH control loop remains unchanged for the DRMI 1F lock.

Figure 1 shows the OLTF of the MICH control loop with the DRMI 1F lock engaged.
The red and blue traces represent the results after and before the above modifications, respectively.
Although the transfer function from OUT to IN1 was increased, the OLTF gain was kept essentially unchanged.

Figure 2 compares the measured plant after the modification with a plant model estimated from the OpLev response.
The measured plant is in reasonable agreement with the model.

Note:

The calibration does not currently take into account the 45-degree incidence angle of the BS. Therefore, the calibration factor should be corrected by approximately 1.4.

Takahashi-san reported that the gradual increase of temperature in the corner station and warned of the limitation of the height adjustment of GAS systems.

Then Hayakawa-kun and I performed the following adjustment on July 24 (Friday),

• IXV: Off the Delonghi heater: 600X -> 0W
• In the corner station
  • Precision cooler temp setting: 20C -> 18C
  • Reduction of number of operated FFUs: SR-area SR3: 2 -> 1
    BS-SR2: 3 -> 2
    BS-BS:  5 -> 4
    BS-PR2: 3 -> 2
    PR-PR3: 3 -> 2
    PR-PRM: 3 -> 2

Then, the temp in IXV decreased by ~ 0.5C, and the temp around PR/BS decreased by ~ 0.3C. We need the GAS adjustment, especially for IX.