[Kataoka, Sugioka, Fujimoto, Ushiba, Hirose]

Overview

Since the MICH and SRCL signals at RF51 are likely to have similar demodulation phases, we wrote a Python script to measure the RF signals while sweeping the demodulation phase. The script was developed for DRMI commissioning based on the script of klog36343. (/users/cHirose/script/schnupp_asymmetry_measurement_DRMI.py)

1. RF51 demodulation phase sweep with MICH excitation 

We first measured the RF51 signal while exciting MICH.

• Excitation frequency: 210 Hz

• OSC CLK gain: 30000

• S/N ratio: approximately 3（When RF51 demodulation phase: −145 deg）

The measured signal did not show a clear sinusoidal dependence on the demodulation phase, possibly due to the low S/N ratio.
In addition, the excitation amplitude of 50000 was directly applied to the OUTPUT matrix, which may have been too large. The DRMI 1f lock was lost during the measurement.
Therefore, the phase sweep could only be performed from −180 deg to −23 deg (FIg1, FIG2).

2. RF51 demodulation phase sweep with SRCL excitation

Next, we measured the RF51 signal while exciting SRCL.

• OSC CLK gain: 5000

• S/N ratio: greater than 10（When RF51 demodulation phase: −180 deg）

The measured signal showed a clear sinusoidal dependence on the demodulation phase.
At the current RF51 demodulation phase setting for 3f (−145 deg), the Q signal was close to its minimum, as expected.(FIg3, FIG4)

3. RF135 demodulation phase sweep with MICH excitation 

Finally, we measured the RF135 signal while exciting MICH.(FIg5, FIG6)

• Excitation frequency: 210 Hz

• OSC CLK gain: 50000

• S/N ratio: approximately 10（When RF135 demodulation phase: −180 deg）

The S/N ratio of RF135 was better than that of RF51 under the same MICH excitation conditions. 
Currently, the RF135 demodulation phase is set to -119.8 deg, where the RF135 I signal is maximized for PRCL excitation. 
It seems difficult to achieve coupling between MICH and PRCL due to the phasing of RF135.

[Ushiba, Hirose, Aritomi, Fujimoto, Kataoka, Sugioka]

Abstract:

To construct input matrix for DRMI3F and decouple each signals, we measured coupling levels.
We then assessed the 3f signals and attempted the 1f-to-3f handover. 
The handover failed, and it is likely that the MICH signal is still not sufficiently decoupled.

Details:

We measured the MICH-, PRCL-, and SRCL-to-3f PD signal transfer functions (TFs) while DRMI 1f was locked. 
We injected a 150.125 Hz excitation into each DoF 1f control loop and measured the TF from the 1f IN1 signal to the 3f PD signal. 
Since the IN1 signal is calibrated in nanometers, the gain is calibrated in dBcnt/nm.

The measurements were performed with the REFL51 demodulation phase set to  145(Figure.1) and 130(Figure.2)(as detailed in klog37830).
The left/middle/right pads shows the measurements under PRCL/SRCL/MICH excitation, respectively.
In both demodulation phase cases, the MICH-to-REFL51Q gain was remarkably small even compared to MICH-to-REFL51I.
This might imply that MICH signal is either in phase or in antiphase with PRCL and SRCL.

Based on these measurements, we constructed the 3f control signal and evaluated it. This part was performed exclusively with a demodulation phase of 145°.
We constructed a 3*3 matrix with nine each measured TF gain, and used the inverse of this matrix for Input Matrix.
We utilized the CARM, DARM, and XARM IN1 channels—which are not currently used for control—as the 3f MICH,PRCL, and SRCL signals.
Then we injected 150.125Hz excitation to each DoF 1f contorl loop again, and measured TF from 1f IN1signal to 3f IN1 signal(Figure.3).
Figure.3 shows that 3f PRCL and SRCL signal is well decoupled.
Although the 3f MICH signal exhibits some coupling from PRCL and SRCL, its coherence is low.
We also measured the OLTF of these 3f signals while DRMI1f locked(Figure.4 for MICH, Figure.5 for PRCL, Figure.6 for SRCL) which generally matched to those of 1f.

Subsequently, we attempted the 1f-to-3f handover. 
First, we tried the MICH handover, but it was unsuccessful. 
Next, we attempted to hand over PRCL and SRCL first, followed by MICH control. 
The PRCL handover—which had already been achieved yesterday—was successful, but PRCL 3f was unstable, and the SRCL handover attempt was skipped.

Plans:

There are several potential approaches for DRMI 3f locking:

1. The surprisingly weak MICH signal in REFL51Q is unusual; therefore, further investigation was conducted, which will be posted by Hirose-san later.

2. Taking the SRCL signal from another port and using REFL51I for MICH should also be feasible.

3. There is a possibility that imperfect phasing and decoupling in 1f compromised the matrix adjustment. Consequently, further fine-tuning of the 1f control could serve as a solution.

[Kataoka, Sugioka, Hirose, Aritomi, Tanaka (online), Komori (online), Ushiba, Fujimoto]

Abstract

We performed decoupling and calibration of the DRMI 3f sensors.
We also attempted to lock the DRMI using the calibrated 3f signals. We successfully performed the 1f-to-3f transition for PRCL and SRCL individually.
However, the transition for MICH was unsuccessful. Further adjustments, such as optimizing the error signal offset and improving the sensor decoupling, are likely necessary.

Details: DRMI 3f sensor decoupling

Since we successfully locked the DRMI with 1f signals yesterday, we used the 1f-locked state to perform decoupling of the 3f sensors.

REFL135-I demodulation phase adjustment

While the DRMI was locked with 1f signals, we excited the PRM at a frequency outside the PRCL control bandwidth and adjusted the REFL135 demodulation phase to minimize the peak in the REFL135-Q spectrum.
The demodulation phase was changed as follows, and the resulting spectra are shown in Fig. 1.

• K1:LSC-REFL_PDA2_RF135_PHASE_R: 60.2 ⇒ -119.8

REFL51-I/Q demodulation phase adjustment

While the DRMI was locked with 1f signals, we excited the SRM at a frequency outside the SRCL control bandwidth and adjusted the REFL51 demodulation phase to minimize the peak in the REFL51-Q spectrum (i.e., to minimize the SRCL coupling).
The demodulation phase was changed as follows, and the resulting spectra are shown in Fig. 2.

• K1:LSC-REFL_PDA2_RF51_PHASE_R: -35 ⇒ 145

Reduction of PRCL-to-SRCL coupling

Since REFL51-I contains PRCL coupling, we decoupled the SRCL signal by subtracting REFL135-I from REFL51-I.

First, while the DRMI was locked with 1f signals, we excited the PRM at a frequency outside the control bandwidth and measured the transfer function from REFL135-I to REFL51-I at the excitation frequency.
We then entered the measured value into the input matrix to subtract the PRCL contribution from REFL51-I.
To check the spectrum of the decoupled REFL51-I signal, we routed it through the unused CARM filter bank and monitored its IN1 signal.

Fig. 3 shows the spectra of the raw REFL51-I signal and the decoupled signal (K1:LSC-CARM_IN1). The PRCL coupling was reduced by at least a factor of approximately 7.
The input matrix values were:

• REFL51-I to CARM: 1.0
• REFL135-I to CARM: -0.218

SRCL 3f calibration

We calibrated the decoupled SRCL 3f signal into nm, as for the 1f signal, by applying a constant scaling factor.

Specifically, while the DRMI was locked with 1f signals, we measured the transfer function from SRCL1_IN2 to CARM_IN1 to obtain the 3f OLTF.
We then adjusted the scaling factors in the input matrix so that the 3f OLTF matched the 1f OLTF.

Fig. 4 shows the 1f OLTF and the calibrated 3f OLTF for SRCL.
The input matrix values were:

• REFL51-I to CARM: 4.45
• REFL135-I to CARM: -0.969

Reduction of SRCL-to-PRCL coupling

Since REFL135-I may also contain SRCL coupling, we decoupled the PRCL signal by subtracting REFL51-I from REFL135-I.

First, while the DRMI was locked with 1f signals, we excited the SRM at a frequency outside the control bandwidth and measured the transfer function from REFL51-I to REFL135-I at the excitation frequency.
We then entered the measured value into the input matrix to subtract the SRCL contribution from REFL135-I.
To check the spectrum of the decoupled REFL135-I signal, we routed it through the unused CARM filter bank and monitored its IN1 signal.

Fig. 5 shows the spectra of the raw REFL135-I signal and the decoupled signal (K1:LSC-CARM_IN1). The SRCL coupling was reduced to the noise floor, corresponding to a reduction of at least approximately one order of magnitude.
The input matrix values were:

• REFL135-I to CARM: 1.0
• REFL51-I to CARM: -1.8

*Note: While writing this report, I noticed that the noise floor increased by approximately a factor of 2 after the subtraction. This is because the relatively noisy REFL51-I signal was used for the subtraction, adding noise to the decoupled signal.
However, as described below, we were able to lock PRCL with the 3f signal alone, so this increase in the noise level may not be a serious problem.

PRCL 3f calibration

We calibrated the decoupled PRCL 3f signal into nm, as for the 1f signal, by applying a constant scaling factor.

Specifically, while the DRMI was locked with 1f signals, we measured the transfer function from PRCL1_IN2 to CARM_IN1 to obtain the 3f OLTF.
We then adjusted the scaling factors in the input matrix so that the 3f OLTF matched the 1f OLTF.
Fig. 6 shows the 1f OLTF and the calibrated 3f OLTF for PRCL.

The input matrix values were:

• REFL135-I to CARM: 0.208
• REFL51-I to CARM: -0.375

Reduction of PRCL-to-MICH coupling

We decoupled the MICH signal by subtracting REFL135-I from REFL51-Q.

First, while the DRMI was locked with 1f signals, we excited the PRM at a frequency outside the control bandwidth and measured the transfer function from REFL135-I to REFL51-Q at the excitation frequency.
We then entered the measured value into the input matrix to subtract the PRCL contribution from REFL51-Q.
To check the spectrum of the decoupled REFL51-Q signal, we routed it through the unused CARM filter bank and monitored its IN1 signal.

Fig. 7 shows the spectra of the raw REFL51-Q signal and the decoupled signal (K1:LSC-CARM_IN1). However, the PRCL coupling was reduced by only approximately a factor of 2.
The input matrix values were:

• REFL51-Q to CARM: 1.0
• REFL135-I to CARM: -0.05

In this measurement, the peak in the REFL51-Q spectrum was only about 6 times higher than the noise floor. A larger excitation may allow more accurate adjustment in the next measurement.

MICH 3f calibration

We calibrated the decoupled MICH 3f signal into nm, as for the 1f signal, by applying a constant scaling factor.

Specifically, while the DRMI was locked with 1f signals, we measured the transfer function from MICH1_IN2 to CARM_IN1 to obtain the 3f OLTF.
We then adjusted the scaling factors in the input matrix so that the 3f OLTF matched the 1f OLTF.

Fig. 8 shows the 1f OLTF and the calibrated 3f OLTF for MICH.
The input matrix values were:

• REFL51-Q to CARM: 36.7
• REFL135-I to CARM: -1.84

Details: DRMI 3f lock trial

We attempted to lock the DRMI using the calibrated 3f signals described above, together with the filters, gains, and offsets previously used for the 3f lock. However, we could not acquire the lock at all.
Therefore, we investigated the problem by handing over one DOF at a time from 1f to 3f while keeping the other DOFs locked with 1f signals.

PRCL 3f handover (successful)

We successfully handed over PRCL from 1f to 3f using the same filters and gain settings as for the 1f lock.

SRCL 3f handover (successful)

When we attempted to hand over SRCL from 1f to 3f using the same filters and gain settings, the feedback signal saturated and the lock was lost.
We then reduced the SRCL1 gain from 1.4 to 0.7, which allowed us to complete the handover without any problems.

MICH 3f handover (unsuccessful)

For MICH, the feedback signal initially saturated, as in the case of SRCL.
We therefore reduced the ELP from 500 to 100 and the gain from 9.0 to 2.0.
With these changes, the feedback signal no longer saturated during the transition. However, AS DC gradually drifted, and the lock was eventually lost.
This suggests that we need to optimize the MICH offset for the 3f signal.
In addition, when we measured the PRCL-to-MICH coupling again after some time, we found that the coupling had become worse.
Furthermore, the gain and phase of the 3f OLTF had changed significantly compared with those measured during the calibration described above.
Further investigation is necessary for MICH.

Plans for tomorrow

When we first succeeded in locking the DRMI with 3f signals (⁠klog 37297), the sensor decoupling was not as well optimized as it is now.
Therefore, we would like to spend a little more time trying to achieve the 3f lock using the parameters adjusted yesterday.

• First, try handing over both PRCL and SRCL to 3f simultaneously.
• Find an appropriate MICH offset for the 3f signal, since an incorrect offset may cause a large MICH detuning during the handover.
• If we want to further improve the MICH decoupling, one possible approach is to choose a different REFL51-I/Q demodulation phase, as discussed in ⁠klog 37830.
• It may also be useful to diagonalize the MICH actuators using the DRMI sensors, as we did previously.

Concerns

Unexplained peak around 14 Hz in the OLTFs

All the OLTFs measured this time, for both 1f and 3f, show an unexplained peak around 14 Hz.
This peak was not present in the OLTFs measured during the recovery work in October (⁠klog 37681).
Although this peak is probably not causing control instability, its origin is still unclear and worth investigating.

Significant change in the MICH optical gain?

In this measurement, the input matrix coefficient required to calibrate REFL51-Q into the MICH error signal in nm was 36.7.
However, during the recovery work in October (⁠klog 37681), this coefficient was 4.8.
Thus, the required coefficient is now almost 7 times larger than before.
This suggests that the MICH optical gain (or possibly the actuator gain?) has decreased to approximately 1/7 of its previous value.
Such a large reduction is not expected from the IMC length adjustment alone, and the cause is currently unknown.

[Sugioka]

Abstract:

I measured the coupling of PRCL and SRCL into the MICH signal in DRMI 3f (REFL51Q) with various demodulation phases for REFL51.

Background:

As will be reported by Fujimoto-san later, we performed REFL51 phasing by minimizing the peak in REFL51Q while DRMI1f locked and SRCL was excited.
We also set the input matrix to minimize the peak in the MICH signal during PRCL excitation.
We then attempted the DRMI control handover from 1f to 3f; however, the MICH handover failed. 
This indicates that the MICH signal in 3f is not sufficiently decoupled.

Details:

According to Kawakami-kun's simulation (the figure on the right side of the 11th slide in the latter file of JGW-G2617586-v2), there should be an optimal REFL51 demodulation phase that minimizes the PRCL signal. Therefore,minimizing PRCL-to-MICH coupling via phasing and subtracting SRCL using INMTRX is a potential solution for achieving DRMI 3f lock. I measured the coupling of PRCL and SRCL into REFL51Q across various REFL51 demodulation phases.
As Fujimoto-san will post later, SRCL signal was minimized with the demodulation phase of 145 while exciting SRCL.
The three pads in the right side of Figure.1 comfirm this result.
Meanwhile, PRCL signnal was minimized with the demodulation phase of 130 while exciting PRCL, as the three pads in the left side of Figure.1 show.

Since the SRCL/PRCL IN1 is calibrated to nm, the SRCL/PRCL2POP51Q TF gain is also calibrated to dB cnt/nm.

The approximately 15 degree difference between the phases that minimize PRCL and SRCL coupling is consistent with Kawakami-kun's simulation.
However, the measured gain of the PRCL/SRCL2REFL51Q TF appears unreasonable.
PRCL2REFL51Q gain is approximately 4 times larger than that of SRCL2REFL51Q, whereas almost the same value in Kawakami-kun's simulation.

Plans:

There are 3 options for constructiong the MICH signal for 3f control.

1. Minimize the SRCL coupling by phasing and subtract PRCL coupling by INMTRX
With the demodulation phase of 145.
The handover failed using this method previously, but further matrix adjustment may help achieve 3f locking.

2. Minimize the PRCL coupling by phasing and subtract SRCL coupling by INMTRX
With the demodulation phase of 130.

3.Mitigate PRCL and SRCL both by phasing and also adjust INMTRX
With the demodulation phase of 130-140.
 

> Tomorrow, we plan to install and connect patch panels to the racks, as well as test the cables.

We have completed the installation and connection of the patch panels in the rack, as well as cable testing.
Connections:
From 2F EY1 (Fig. 1) to 1F EY0: 12-fiber MTP cable with 3 wires (Fig. 2); to EYA: 2 wires (Fig. 3)

Since the delivery was delayed, only the two wires for EYA have female plugs on both ends.
Ultimately, all connections will have male plugs (with guide pins) on both ends.

I changed the setpoint of the F0 GAS from 4300 to 4250.

This log summarizes the Guardian modifications made during the commissioning work reported in klog 37825.

1. DRMI Guardian updates

[DOWN]

• Set the demodulation phase of POP RF45 to 73.870 deg. We plan to move the DRMI-related settings to the DOWN state, but only this setting has been implemented so far.

[PREP_FM_FOR_DRMI]

• Set the demodulation phases for DRMI 1f locking as follows:

  • POP RF17: -139.60 deg

  • POP RF45: 73.870 deg

• During this commissioning, the demodulation phases were adjusted to maximize POP45I for PRCL and minimize POP17Q for SRCL.

[LOCKING_DRMI_1F]

The following settings were updated.

• Input matrix (INMTRX). To reduce the coupling between the longitudinal DOFs, the following elements were set:

  • POPA45I (MICH) → SRCL: -9.5

  • POPA17I (SRCL) → PRCL: -0.4

  • POPA45I (PRCL) → MICH: 5.3

• MICH offset. Changed the MICH filter OFFSET from -25.8 to -35.0. After this change, the AS port camera image became slightly darker.
• Output matrix (OUTMTRX). These values were taken from the PRMI and SRMI settings, respectively.

  • MICH → PRM: -0.0404

  • MICH → SRM: 0.23479

• PRCL gain. Set PRCL1_GAIN to 0.85 based on the OLTF measurement.

2. SRY initial alignment

[LOCKING_SRC_3F]

• Changed LSC_INMTRX['SRCL', 'POPA17I'] from 80 to -80. The original value of 80 was the same as that used for SRX, but SRY could not be locked with this setting. After reversing the sign, SRY was successfully locked. The reason why the opposite sign was required is still unclear.

[Ushiba, Hirose, Aritomi, Fujimoto, Kataoka, Sugioka]

Abstract:

We performed adjustments for DRMI 1f.

Details:

 We achieved DRMI 1f locking,and completed the phasing, decoupling, calibration, and UGF adjustments for DRMI 1f.

First, we performed phasing for POP90I/AS34I because they are used for thresholds in DRMI locking state.
Since there seemed low coherencein excitation measurement, we tuned the demodulation phase to minimize the offset in timeseries of POP90Q/AS34Q While PRMI3f/SRMI1f locked(Figure.1).
We also updated LSC_CUST_OUT_MTRX in DRMI to reflect the values from PRMI and SRMI.
Then, we achieved DRMI 1f locking.

After DRMI locked, we performed the phasing for POP17 and decoupled SRCL from PRCL IN1.
We injected 150.125Hz excitation to SRCL. Then we changed the demodulation phase from -149.6 to -139.6 to minimize the peak in POP17Q.
We also set the K1:LSC-PD_DOF_MTRX_4_9  -0.4 to minimize the peak in PRCL IN1(Figure.2).

Next, we performed the phasing for POP45 and decoupled PRCL from MICH IN1 and SRCL IN1.
We nnoticed that exciting IN1 causes the contamination by the different G in each control loop, so here we injected 150.125Hz excitation to K1:VIS-PRM_TM_TEST_L_EXC.
Then, the PD signal is just the product of excitation and A(Actuator efficiency) which is independent from control loop.
We changed the demodulation phase from 57.87 to 78.87 to minimize the peak in POP45Q.
We also set the K1:LSC-PD_DOF_MTRX_3_11 5.3 and K1:LSC-PD_DOF_MTRX_4_11 -9.5 to minimize the peak in MICH IN1 and SRCL IN1(Figure.3).

Then, we adjusted control gain.
We measured OLTF for MICH, PRCL and SRCL(Figure.4,5,6).
The UGF for each control was approximately 50Hz, 30Hz and 100Hz.
Out-to-In measurement was consistent with the suspension model, which verifies that the IN1 signal is calibrated to nm.

All of these parameter changes were updated in Guardian,and the specific Guardian modifications will be detailed in Hirose-san’s upcoming post.

YamaT-san, DanChen-san, Nakgaki-san, Infofarm(4 people), Ikeda

We installed fiber-optic cables from the 2nd floor of the Y End to the mini racks near DGS and EYA on the 1st floor.

Tomorrow, we plan to install and connect patch panels to the racks, as well as test the cables.

With Nakagaki-san

We carried out electrical safety improvements in both the EXA and EYA areas.

Work performed

• Replaced or corrected power cables that had been identified as issues in the fire safety assessment.

• Rearranged the cables and equipment so that the power distribution boxes could be properly closed. (pictures)

• Installed dust-proof safety plug covers wherever possible.

Impact on equipment

• The power cables for the network switches were also included in the replacement work. As a result, network communication with devices connected to the Pcal network switches was temporarily interrupted.

• The affected devices included Tcam and  a vacuum monitor in EYA

I offloaded the F0, F3, and BF GAS filters with the FRs.

I changed the setpoint of the F0 GAS from 4200 to 4300.

I measured the IP tilt, which depends on the IP position. The IP position was changed with the setpoint for the LVDT L. The IP tilt was measured using the DC feedback signal in the FLDACC H1 (aligned to L). The plot shows that the DC acceleration in the FLDACC is proportional to the IP position. The coefficient was 2.8μg/mm which corresponds to 2.8μrad/mm in tilt.

This log summarizes the Guardian updates described in klog37816. (SRY locking and the SRC initial alignment have not been tested yet.)

1. Updates to lsclib.py

• The lock threshold for SRMI 3f (is_srmi3f_locked) was added: ezca['LSC-AS_PDA2_RF34_I_NORM_MON'] > 0.05
  This is the same threshold as that used for SRMI 1f. Unlike PRMI, both SRMI 1f and 3f have the 1f sidebands resonating in the interferometer, while the carrier is dark at the AS port due to the Schnupp asymmetry. Therefore, the same 2f1 RFPD signal is used to determine the lock status for both SRMI 1f and 3f.
• The @check_srmi3f decorator was also added.

2. SRX 1f/3f commissioning

[PREP_FM_FOR_SRC]

This state is shared by SRX and SRY, although SRY has not been tested.

• The SRCL1 gain is set to 0.02 for 1f and 0.015 for 3f.

• The HWP angle is set to 146 deg.

[LOCKING_SRC_3F]

In the DOWN state, LSC_INMTRX['SRCL','REFL51I'] is set to 1 by default.

For 1f locking:

• The default SRCL -> REFL51I input matrix element is cleared, and SRCL -> POP17I is set to 80.

• ELP100 is enabled.

• The POP17 demodulation phase is set to 153.00 deg.

For 3f locking:

• SRCL -> REFL51I is set to 200.

• ELP500 is enabled.

• The REFL51 demodulation phase is set to 130.100 deg.

Previously, this state only checked is_src1f_locked. Since the same state is now used for 3f locking, the is_src3f_locked condition was also added.

3. SRMI 1f/3f commissioning

[PREP_FM_FOR_SRMI]

• The HWP angle is set to 140 deg.
• The demodulation phase is set to:  1f: -149.60 deg, 3f: 70.100 deg
  For 1f locking, MICH and SRCL are sensed using POP17Q and POP17I, respectively. Considering that the SRCL signal may be larger than the MICH signal, the demodulation phase was adjusted to minimize the SRCL contribution in POP17Q.
• For both 1f and 3f locking, the output matrix elements from MICH to BS and SRM are configured. MICH -> BS is already set to 1 by default. In this state, MICH -> SRM is additionally set to 0.23479. This value was estimated from the theoretical ratio and measured responses of BS and SRM during SRX commissioning, in order to predict the coupling between MICH and SRCL in SRMI. With this setting, the SRMI control loops were stable after lock acquisition. This is the same approach as that used when transitioning from PRY to PRMI in klog37812.

[LOCKING_SRMI]

• The default input matrix elements configured in the DOWN state are cleared before setting the SRMI input matrix.
  For SRMI 1f, the following elements are set: LSC_INMTRX['MICH','POPA17Q'] = 57.5, LSC_INMTRX['SRCL','POPA17I'] = 13.335
  For SRMI 3f, the following elements are set: LSC_INMTRX['MICH','REFL51Q'] = -176.4, LSC_INMTRX['SRCL','REFL51I'] = 66.976
• For both 1f and 3f locking, the following settings are applied:

  • MICH2: ELP100 ON and ELP500 OFF.

  • SRCL2: ELP500 ON.

  • MICH1 gain: 0.081.

  • SRCL1 gain: 0.297.

  • When the interferometer approaches resonance, the SRCL2 and MICH2 gains are set to -0.1 and 60, respectively.

• Previously, only is_srmi1f_locked was used to check the lock status. The is_srmi3f_locked condition was added to support SRMI 3f locking.

[SRMI_3F_LOCKED]

• The @check_srmi3f decorator was added to monitor the SRMI 3f lock status.

[Ushiba, Hirose, Kataoka, Sugioka]

Abstract:

We performed adjustments for SRMI 1f and 3f. SRMI1f adjustments were conducted in the same way as PRMI(klog 37812).
Then SRMI3f lock was achieved by copying the control conditions from that of 1f.

Details:

SRMI 1f

We achieved SRMI 1f locking,and completed the phasing, decoupling, calibration, and UGF adjustments for SRMI 1f.

First, we performed the phasing and gain adjustment for SRX(Figure.1).
We changed ELP500 filter to ELP100 in order to avoid the output signal saturation, and SRX was succesfully locked.

Next, we locked SRMI 1f and performed the phasing for POP17 by injecting a 110.125 Hz excitation into K1:LSC-SRCL1_EXC. 
We tuned the demodulation phase to minimize the peak in POP17Q(Figure.2). 

Then, we addressed the decoupling between SRCL and MICH. These channels exhibit an inherent MICH-to-SRCL actuator coupling. 
This cloupling is originated from using only BS as the MICH actuator, since moving BS inherently causes fluctuations in SRCL as well. 
To eliminate this fundamental actuator coupling, we decoupled the actuators by adjusting the output matrix. 
The value to be set in K1:LSC-OUTPUT_MTRX_6_1 represents the ratio of the SRCL length fluctuations caused by BS versus SRM. The actuator efficiencies were measured by taking transfer functions from excitations of SRM and BS to the SRX length with SRX locked(Figure.3). Since the difference between these responses was -6.586 dB, a value of 0.23479—accounting for an additional factor of 2 due to the difference in the BS position's impact on SRCL and SRY—was entered into K1:LSC-OUTPUT_MTRX_6_1.

We then performed OLTF measurements for calibration and UGF adjustments. Sensor calibration was conducted while monitoring the Out-to-In TF, whereas UGF adjustments were made by monitoring the OLTFs, for both MICH and SRCL(Figure.4,5). During the sensor calibration, we updated the INMTRX values and simultaneously adjusted the filter gains to maintain the overall control gain. For the UGF adjustment, we fine-tuned the filter gains,resulting in a UGF of ~20 Hz for MICH and ~40 Hz for SRCL. 

SRMI 3f

For SRMI 3f, we performed the phasing for REFL51 while SRCL1f was locked(Figure.6), and we copied the control conditions from SRMI1f.
We measured the TF from POP17I/Q-to-REFL51I/Q while exciting SRCL/MICH at 110.125Hz(Figure.7,8). 
Then we multiplied the inverse of TF gain to 1f-INMTRX in order to make the 3f-INMTRX.
Measured TF gain for I/Q was -14.374dB/-9.735dB, so we set 3f-INMTRX for SRCL/MICH 66.976/176.4 while 1f-INMTRX was 13.335/57.5.
We put -1 gain filter in MICH1 FM2 because the phase of TF POP17Q2REFL51Q was ~180degree.
Since the control condition for 3f is exactly the same as that of 1f, SRMI 3f control was achieved and OLTF measurement matched to that of 1f very well(FIgure.9,10).

All of these parameter changes were updated in Guardian,and the specific Guardian modifications will be detailed in Hirose-san’s upcoming post.

Here is a brief summary of the procedure for PRMI 3f locking.

First, we attempted to switch from PRMI 1f to 3f locking by adding the 3f signal ratios measured during 1f locking to the INMTRX. However, we could not achieve stable 3f locking with this method.

Therefore, we restored the gains, INMTRX, and demodulation phases to the settings that had successfully achieved PRMI 3f locking earlier in the morning. We also applied the same OUTMTRX settings as those used for PRMI 1f locking. With these settings, we successfully locked PRMI 3f.

After achieving the lock, we readjusted the demodulation phases (FIG1 and FIG2).

The OLTF measurements and decoupling adjustments are described in Sugioka-kun's klog37812.

These settings have been implemented in the Guardian, as described in klog37813.

This is a summary of the Guardian modifications described in klog 37812.

1. Changes to the Guardian paths

• The original path between DOWN and LOCK_PREP_FOR_OBSERVATION has been disconnected. This path was previously used for the transition from DOWN to PRMI_3F_LOCKED. The observation path in the VERTEX Guardian will be modified for DRMI locking in the future. The settings in the DOWN state have not been changed. The parameters used for PRMI 1f/3f locking are reset in the DOWN state. PRMI_3F_LOCKED can now be reached from LOCKING_PRMI, which is on the path DOWN → LOCKING_PRMI → PRMI_1F_LOCKED. The settings in LOCKING_PRMI are now selected depending on whether PRMI 1f or 3f locking is requested.

2. Changes to each state

[PREP_FM_FOR_PRMI]

• [Demodulation phases] The demodulation phases are set separately for PRMI 1f and 3f locking. For each degree of freedom, the demodulation phase was optimized so that the signal appears mainly in either the I or Q phase. Previously, the demodulation phases were adjusted for MICH and PRX 1f/3f locking. This time, the phases were re-optimized under PRMI locking conditions, and the values were updated accordingly.
• [Output matrix] The OUTMTRX coefficient was set to -0.0404 to send the MICH feedback signal to BS and PRM. The same coefficient is used for both PRMI 1f and 3f locking.

• [HWP setting] During PRMI 3f locking, the REFL optical power was too high. Therefore, the HWP angle was changed from 140 deg to 160 deg. The HWP is now set to 160 deg in this state.

[LOCKING_PRMI]

The input matrix and feedback gains are configured according to the requested locking mode.

For PRMI 1f locking (PRMI_1F_LOCKED request):

• INMTRX:

  • POP17Q, POP45I → MICH

  • POP45I → PRCL

• The gains of MICH1 and PRCL1 are applied first.

• Once the signals exceed the thresholds, the gains of MICH2 and PRCL2 are applied.

For PRMI 3f locking (PRMI_3F_LOCKED request):

• INMTRX:

  • REFL51I → MICH

  • REFL51I, POP135I → PRCL

• The gains of MICH1 and PRCL1 are applied first.

• Once the signals exceed the thresholds, the gains of MICH2 and PRCL2 are applied.

The same filters are used for both PRMI 1f and 3f locking.

[PRMI_3F_LOCKED]

• This state is now connected to LOCKING_PRMI. Previously, it was connected to LOCKING_PRMI_FOR_OBSERVATION. The state index remains unchanged.

[PRMI_3F_LOCKED_FOR_OBSERVATION]

• This is the former PRMI_3F_LOCKED state, which was connected to LOCKING_PRMI_FOR_OBSERVATION. The state index was changed from 450 to 460.

3. Current status

• PRMI 3f is currently locked using the VERTEX Guardian with the PRMI_3F_LOCKED request. At the same time, PRMI ADS is requested through the ASC_LOCK Guardian. The interferometer remains stable under these conditions. The Initial Alignment Guardian has not yet been tested. The HWP settings used in the PRMI path of the Initial Alignment Guardian and the VERTEX Guardian are identical. Therefore, no conflict due to the HWP settings is expected.

[Ushiba, Hirose, Kataoka, Sugioka]

Abstract:

We performed adjustments for PRMI 1f and 3f. Details regarding the PRMI 3f locking and phasing will be posted separately by Hirose-san.

Details:

PRMI 1f

For PRMI 1f, we completed the phasing, decoupling, calibration, and UGF adjustments.

 First, we performed the phasing for POP17 and POP45 by injecting a 100.125 Hz excitation into both K1:LSC-MICH1_EXC and K1:LSC-PRCL1_EXC. 
We tuned the demodulation phase to minimize the peaks in POP17Q and POP45I, which resulted in changing K1:LSC_POP_PDA1_RF17_PHASE_R from -141.0 to -96.0(Figure.1). 
The initial value for K1:LSC_POP_PDA1_RF45_PHASE_R (57.870) was found to be already optimized.

Next, we addressed the decoupling between PRCL and MICH. These channels exhibit sensor coupling alongside an inherent MICH-to-PRCL actuator coupling. 
The PRCL-to-MICH sensor decoupling was conducted by entering an appropriate value into K1:LSC-PD_DOF_MTRX_3_11. 
This value corresponds to the ratio of the peak heights in POP17Q and POP45I when exciting PRCL at 100.125 Hz.
The upper left pad in Figure.2 shows the spectrum of MICH signal before and after MTRX adjustment.

Coupling between the MICH and PRCL actuators was also observed, which originated from using only BS as the MICH actuator, since moving BS inherently causes fluctuations in PRCL as well. To eliminate this fundamental actuator coupling, we decoupled the actuators by adjusting the output matrix. The value to be set in K1:LSC-OUTPUT_MTRX_5_1 represents the ratio of the PRCL length fluctuations caused by BS versus PRM. The actuator efficiencies were measured by taking transfer functions from excitations of PRM and BS to the PRY length with PRY locked(Figure.3). Since the difference between these responses was -22 dB, a value of -0.0404—accounting for an additional factor of 2 due to the difference in the BS position's impact on PRCL and PRY—was entered into K1:LSC-OUTPUT_MTRX_5_1. We skipped the MICH-to-PRCL sensor decoupling because it was already sufficiently decoupled.

We then performed OLTF measurements for calibration and UGF adjustments. Sensor calibration was conducted while monitoring the Out-to-In TF, whereas UGF adjustments were made by monitoring the OLTFs, for both MICH and PRCL(Figure.4,5). During the sensor calibration, we updated the INMTRX values and simultaneously adjusted the filter gains to maintain the overall control gain. For the UGF adjustment, we fine-tuned the filter gains,resulting in a UGF of ~20 Hz for MICH and ~40 Hz for PRCL. 

All of these parameter changes were updated in Guardian,and the specific Guardian modifications will be detailed in Hirose-san’s upcoming post.

PRMI 3f

For PRMI 3f, we performed the decoupling, calibration, and UGF adjustments following the exact same procedure used for 1f(Figure.6,7,8). MICH was sufficiently decoupled from PRCL so we didn't perform the decoupling.