Abstract

Details

[Kimura and Yasui]

 We replaced the helium compressor from Xer to P-56 as a countermeasure against the temperature rise in the duct shielded cryo-cooler (Xer).
The compressor replacement took about 10 minutes from 10:40 am to 10:50 am.
After the replacement, the helium compressor was immediately started and cooling of the Xer duct shield resumed.
A trend graph of the pre- and post-operation temperatures is shown below.

 After restart, the temperature at the cold head of the cryo-cooler changed to a downward trend.
 We plan to keep the temperature at this level to check the lowest temperature reached at the cold head of the cryo-cooler.

[Carl, Haoyu]
We found the drift monitors on the VIS_ALL medm screen were not working.  We made a local copy of the VIS_ALL screen that can be acessed from the VIS_WORKSPACE screen.  To get the drift monitors working the following was done.  The temporary file is located /users/haoyu/20250130/VIS_ALL.adl. An example drift monitor output is attached.

Channel changes
K1:VIS-BS_TM_OPLEV_PIT_DIAG_DQ to K1:VIS-BS_TM_OLDAMP_P_IN1_DQ
K1:VIS-BS_TM_OPLEV_YAW_DIAG_DQ to K1:VIS-BS_TM_OLDAMP_Y_IN1_DQ
For each test mass with DIAG channels
K1:VIS-PR3_TM_OPLEV_TILT_PIT_OUT_DQ to K1:VIS-PR3_TM_OLDAMP_P_IN1_DQ
K1:VIS-PR3_TM_OPLEV_TILT_YAW_OUT_DQ to K1:VIS-PR3_TM_OLDAMP_Y_IN1_DQ
For each test mass with TILT channels
K1:VIS-IMMT2_TM_OPLEV_YAW_OUT_DQ to K1:VIS-IMMT2_TM_OLDAMP_Y_IN1_DQ
K1:VIS-IMMT2_TM_OPLEV_YAW_OUT_DQ to K1:VIS-IMMT2_TM_OLDAMP_Y_IN1_DQ
for test masses with OPLEV channels

Added
 . K1:VIS-BS_TM_OLDAMP_L_IN1_DQ K1:VIS-SRM_TM_OLDAMP_L_IN1_DQ K1:VIS-SR2_TM_OLDAMP_L_IN1_DQ K1:VIS-SR3_TM_OLDAMP_L_IN1_DQ
and 
 . K1:VIS-PRM_TM_OLDAMP_L_IN1_DQ K1:VIS-PR2_TM_OLDAMP_L_IN1_DQ K1:VIS-PR3_TM_OLDAMP_L_IN1_DQ
and 
 . K1:VIS-IMMT1_TM_OLDAMP_L_IN1_DQ K1:VIS-IMMT2_TM_OLDAMP_L_IN1_DQ
and
 . K1:VIS-MCI_TM_OLDAMP_L_IN1_DQ K1:VIS-MCE_TM_OLDAMP_L_IN1_DQ K1:VIS-MCO_TM_OLDAMP_L_IN1_DQ
added
 . K1:VIS-ITMX_TM_OLDAMP_L_IN1_DQ  K1:VIS-ETMX_TM_OLDAMP_L_IN1_DQ K1:VIS-ITMY_TM_OLDAMP_L_IN1_DQ K1:VIS-ETMY_TM_OLDAMP_L_IN1_DQ 

Removed
OLDCCTRL channels as there is no longer any optical lever DC control to the MN stage. 

[Yamaguchi, Oshima, Komori]

We excited roll resonances around 54Hz in MN, and measured the resonant frequency and Q-value of the roll in the CuBe wire between IM and MN.
We used the ports for exciting:
K1:VIS-ITMX_MN_TEST_R_EXC
K1:VIS-ETMX_MN_TEST_R_EXC

The starting times for ringdown and signals, which can be used for Q measurement, for each suspension are as follows:
ITMX:
01:50:45 UTC: K1:VIS-ITMX_NBDAMP_R2_OUT_DQ
ETMX:
02:44:25 UTC: K1:VIS-ETMX_NBDAMP_R2_OUT_DQ

We estimated the Q factors of the roll mode of the CuBe wires, corresponding to the Q factors derived from the ringdown measurement. The results are presented in the attached figure and summarized in the following list.
 

The estimation errors for the resonant frequency and the Q-value are 5 mHz and 0.1e3, respectively.
 

[Carl, Haoyu]

We propose that the violin modes could be actively damped.  Also that notching violin mode freqencies in control paths could reduce mode excitations.
This could potentionally give a factor of 10 improved sensitivity between 176Hz and 186Hz during some recent lock stretches.  First attached figure top panel shows violin mode spectrum during some recent lock stretches (Dec and Jan).  The blue trace shows a trace where a factor of 10 to 100 reduction in mode amplitude could gain significant bandwidth sensitivity in DARM. The most recent trace from 22 Jan is similar to the red trace with low violin mode amplitude.
The violin modes are often small in amplitude in the figure, however we identify several times when the amplitude of individual modes grows dramatically during lock. One such transient is shown as a sequence of PSD (fig 1 bottom panel).  It grows in amplitude in a few seconds then rings down over a minute of so (03:13:00 31/12/2024 UTC).
We guess this must be the result of some control loop driving the modes (or intentional driving), notching violin mode frequencies in control loops that actuate on IM (probably pitch vertical and roll) may be a way to avoid these transients in violin mode amplitude and active damping may be able to reduce amplitudes faster and to a lower level after excitation.

In klog31963 excitation and ring down measurements of violin modes is described.   We understand the drive signal to excite the modes is IM pitch.

We therefore propose that the DARM signal could be fed back to IM pitch to actively damp violin modes.
A model change would be required to send the DARM signal to a VIS model to damp one violin mode.  Cartoon of where this change would be required in the RCG is shown in the second attached figure. The VIS models would also require DARM from IPCx_PCIE if this is available on VIS computers.  This type of damping has been used at LIGO Livingston for violin mode and bounce and roll mode damping.   Also similar notching of control signals (in addition to existing notches in damping filters) may decrease excitation of lower frequency suspension modes from glitches.

Thank you for your suggestions.

In fact, we already have feedback paths from LSC/ASC signals to any stages/DoFs of Type-A payload.
So, please use NBDAMP blocks if you would like to try to test violin mode damping.

Note that NBDAMP filters are implemented into the different model, feedback signals will be delayed by 2 sampling for sending the signals between models (but hopefully not so problematic because the sampling rate is high enough compared with the violin mode frequency).

Thank you for the revisiting calculation. If the IMMT1T QPD is calibrated, the real readout noise spectral density could be compared with your calculation to confirm if limited by shot noise or not! Maybe RIN would be sufficiently suppressed when ISS on.

Abstract:

I calculated IMMT1T QPD fundamental noise.
In the current condition, IMMT1T QPD noise should be limited by shot noise, so SNR will be improved if we increase the laser power to 10W.

Detail:

To investigate the better parameter for IMMT1T QPDs, I calculated the fundamental noise level with current parameter.
What I used for the calcuation is following documents:
QPD circuit: JGW-D1402411-v3
QPD characteristic: S5981 datasheet
OPamp characteristic: LT1114 datasheet

Total output noise of the transimpedance amplifier can be calculated as the summation of the following 5 noises:
1. Voltage noise of OP amp
2. Current noise of OP amp
3. Thermal noise of transimpedance resistance
4. Dark noise of QPD
5. Shot noise of QPD

Voltage noise of OP amp:

According to the datasheet of LT1114, maximum input voltage noise is 2.8e-8 V/rtHz above 10Hz.

Current noise of OP amp:

According to the datasheet of LT1114, maximum input voltage noise is 0.03 pA/rtHz above 10Hz.
Since curret transimpedance resistance is 20k Ohms, output voltage noise due to OP amp current noise is 0.03 pA/rtHz * 20k Ohms = 6.0e-10 V/rtHz

Thermal noise of transimpedance resistance:

The transimpedance resistance (R) is 20k Ohmas and temperature is about 300 K, so the thermal noise of the resistance is sqrt(4*k_B*T*R) = 1.8e-8 V/rtHz, where k_B and T are the Boltzman constant and absolute temperature of the resistance, respectively.

Dark current noise of QPD:

According to the datasheet of LT1114, maximum dark current (Id) of QPD is 4 nA, so the shot noise of the dark current is sqrt(2*e*Id) = 3.6e-14 A/rtHz, where e is an elementary charge.
So, the output voltage noise due to the dark current is 3.6e-14 A/rtHz * 20k Ohms = 7.2e-10 V/rtHz.

Shot noise of QPDs with the current (future) configuration:

If we use 1W (10W) input, IMMT1T trans QPD2 obtained 1W (10W) * 3000 ppm (IMMT1 transmission) * 0.1 (IMMT1T POM transmission) * 0.5 (BS before IMMT1T QPDs) = 1.5e-4 (1.5e-3) W.
According to the datasheet of LT1114, optical efficiency of the QPD is about 0.25 A/W @ 1064nm.
So, the photocurrent (Ip) of the QPD is 0.25 A/W * 1.5e-4 (1.5e-3) W = 8.75e-5 (8.75e-4) A.
Therefore, the shot noise of photocurrent is sqrt(2*e*Ip) = 3.5e-12 (1.1 e-11) A/rtHz.
Since the transimpedance resistance is 20k Ohms, output voltage due to the shot noise of photo current is 3.5e-12 (1.1e-11) A/rtHz * 20k Ohms = 6.9e-8 (2.2e-7) V/rtHz.

Summary:

Since photo current shot noise is the largest in both cases, current IMMT1T QPD noise seems to be limited by shot noise.
So, if we increase the laser power, SNR wll improve by sqrt(10).

According to the figure attached in previous post, GRY TR NORM fluctuation seems large though GRY TR NORM value seems not so small.
So, please check GRY NORM TRANS fluctuation when GRY PNC fringe was large.
Since GRY NORM value depends on the GRY condition (polarization of GRY fiber output?), it might happen that the GRY alignment becomes bad even though GRY TRANS NORM is close to 1.
Please see klog30234 to know how to perform GRY alignment with PICO motor.

With Shingo Hido

Background

As reported, we evaluated parameters for the photon calibrators (Pcals).
Based on the results, we updated these parameters in the real-time system.

Summary

• The values of 1/rho_TS, TS/GSK, and GSK/WSK were set to 1.
• The values of WSK/TxPD1, WSK/TxPD2, and WSK/RxPD were set to be the evaluated rho of each power meter (integrating sphere).
• The final displacement value with the HIGH_POWER_RX_MON state changed by approximately 1% for each Pcal, which is within expectations.
• The SDF was cleared in the SAFE state after all changes.

Details

Parameter Inputs

XPcal rho [V/W]

• TxPD1: -1.89662
• TxPD2: -2.57611
• RxPD: -0.66582
• Optical efficiency Path 1:
  • Measured total: 0.96760
  • Input at each Tx/Rx side: 0.98380
• Optical efficiency Path 2:
  • Measured total: 0.95152
  • Input at each Tx/Rx side: 0.97576

YPcal rho [V/W]

• TxPD1: -2.99776
• TxPD2: -1.11362
• RxPD: -0.54349
• Optical efficiency Path 1:
  • Measured total: 0.98271
  • Input at each Tx/Rx side: 0.99135
• Optical efficiency Path 2:
  • Measured total: 0.9720
  • Input at each Tx/Rx side: 0.98600

Notes

• During the update of the PcalX parameters, we mistakenly entered the reciprocal values for the conversion factors of TxPD1, TxPD2, and RxPD. These values were subsequently corrected.
• Since the evaluated rho values above have units of V/W, their reciprocals needed to be input into the real-time system.

Fig. 1 show the fringe when GR locked with only Y-arm during the lock trial and after the initial alignment in last night. Current, the fringe amplitude is ~1000, this is about smaller than the previous one (~4000) in klog30303.

On the other hand, We also confirmed that PNCX frige. Fig.2 show the fringe when GR locked with only X-arm during the initial alignment in last nigh. In GRX case, the fringe amplitude (~640) seems to be slightly lower than the previous one (~720) in klog29848.

> However, when we read the numpy binary, including the trend data, It didn't work for some reason. I need to update the manual. At least, when we read the numpy file, we need the allow_picke option, such as `np.load(fname, allow_pickle=True)`.

This issue was caused by how to pack the numpy binary file and was unrelated to the jupyter notebook. I fixed it. Using the manual, you can read the binary file, including the trend data.

Thank you for your comments, Ushiba-san and Akutsu-san.

We have the small visibility issue in the PNC of GRY.
The GRY trans. power is still around 1.0, so we think the green power at the output of the fiber or the input alighnment of the green have not been degraded.
Therefore, we have a plan to enter the mine to recover the visibility in the afternoon at this moment.

Just for memo (repeating what I mentioned in this morning): it might be also worth checking what is the green light power at the output of the fiber on the POP table, if the max of the PNC Michelson fringe readout would reduce compared with that of the previous healthy days.

>On the other hand, according to Ushiba-san, there are a high pass filter in the IP_BLEND_ACC{L,T,Y} filter after ACCBLEND_FLDACC{L.T,Y}_OUT so the large DC value in those OUT should be cause of the saturation of IP controls. However, the cutoff frequency (80mHz) of high pass filters seems to be faster that the one (0.1 mHz) of the integrater so the DC value seems to remain in IP_BLEND_ACC{L,T,Y}_IN1. So if the guardian go to LOCK_ACQUISITION even though the DC value in IP_BLEND_ACC{L,T,Y}_IN1 still large, the saturation of IP controls will occur.

Even though IP_BLEND_ACC{L,T,Y}_IN1 is large at DC, it should be fine because there are high-pass filters at IP_BLEND_ACC{L,T,Y} filter banks and DC values are cut.
However, since high-pass filter cutoff frequency is 50/80mHz and not so fast, if we requested LOCK_ACQUISITION soon after the suspension is tripped, IP_BLEND_ACC{L,T,Y}_OUT values can be still high, which causes large feedback signals to IP when switching IP caontrol to inertial damping.
So, we need to wait engaging inertial damping control of IP until IP_BLEND_ACC{L,T,Y}_OUT values become small enough (enough longer than the time constant of high-pass filter).
Now, new function was implemented into the guardian (klog32491), this problem can be avoidable.

We don't have pico motors to align PNC remotely (we have pico motors for green beam but they moves not only reflected beam but also injection beam to the arms),
So, the alignment of PNC is really bad, it is necessary to manually align the optics at POP/POS table.

I'm not so sure the current situation but PNC fringe can be often recovered by just performing initial alignment to recover the GRX/Y alignment.

Komori, Tanaka

## What we did

• We measured the TF from the TM actuator to TM oplev by injecting a white noise from CHARD_{P,Y}_SM_EXC. At that time, in order not to excite the MN stage, we turned off MN_LOCK_OUTSW_{P,Y} in advance.
• This time, we adjusted the OUTMTRX element value for ITMX, ITMY, and ETMY, respectively from the ratios between ETMX and the others at 0.1 Hz in the P case or at 1 Hz in the Y case which frequencies are near each UGF so that each DC gain get the same.
• Then, we measued the TF from the MN actuator to TM oplev with current LOCK filters by injecting a white noise from CHARD_{P,Y}_SM_EXC. At that time, in order not to excite the TM stage, we turned off TM_LOCK_OUTSW_{P,Y} in advance.
• We adjusted the overall gain of MN_LOCK filters to make the crossover frequency 0.1 Hz. Fig. 1 (PIT) and Fig.2 (YAW) show the results. The cross over seems to be 0.1 Hz, the DC gain seems to be almost the same. We use these actuators to try to lock ASC.

## Note

I made a mistake to apply too large excitation (~6000 cnts) to the MN stage in performing the above TF measurement. And then, ITMX and ITMY got tripped because the NBDAMP_Y4 with TM oplev signal kicked BF YAW due to TM oplev got out of range by exciting MN largly and reached the BF RMS to the WD threshold.

After this RMS calmed down, I requested the LOCK_ACQUISITION to ITMX and ITMY guardians but they stopped in the CALM_DOWN state maybe because the IP control seems to be saturated. At once, we set ITMY and ITMX to SAFE state

ACCBLEND_FLDACC{L.T,Y}_OUT and IP_FLDACCINF_H{1,2,3}_OUT seems to be stored much larger value than usual due to this trip. I and Yokozawa-san tried to clear their integrator history and then we could restore ITMX and ITMY to LOCK_ACQUISITION.

On the other hand, according to Ushiba-san, there are a high pass filter in the IP_BLEND_ACC{L,T,Y} filter after ACCBLEND_FLDACC{L.T,Y}_OUT so the large DC value in those OUT should be cause of the saturation of IP controls. However, the cutoff frequency (80mHz) of high pass filters seems to be faster that the one (0.1 mHz) of the integrater so the DC value seems to remain in IP_BLEND_ACC{L,T,Y}_IN1. So if the guardian go to LOCK_ACQUISITION even though the DC value in IP_BLEND_ACC{L,T,Y}_IN1 still large, the saturation of IP controls will occur. So we ask Yamamoto-san to implement the waiting state to calm down the input value and Yamamoto-san implemented it as reported in klog32491.

[Tanaka, Komori]

Today, we encountered difficulties in the IFO acquisition due to unstable PNC control and frequency kicking of the PRM during PRMI 3F locking.
The instability in PNC control is probably caused by a significant reduction in fringe amplitude, which has dropped below 1000, much lower than the nominal value of above 3000, as shown in klog:30303.
We plan to address and resolve this issue tomorrow by moving picomotors.

[Takidera, Sugioka, Sugimoto]

We also tried to perform a similar CuBe wire ring down measurement on ITMY, but we couldn't excite it well and ran out of time.
Tomorrow, we plan to try again to excite the resonance peak with the candidate frequencies that we couldn't try today.

[Kimura and Yasui]

 We are in the process of installing data loggers to monitor He compressor temperatures.
A data logger has been installed in the center machine rooms.
The temperatures to be monitored are the inlet and outlet temperatures of the He gas heat exchanger and the inlet and outlet temperatures of the circulating oil for cooling. 

[Kimura, Yasui, M.Takahashi and H.Sawada]

 A He compressor and a  valve unit were carried into the X-end machine room.
This is preparatory work for repairing a duct shield cryo-cooler (Xer) that has a tendency to rise in temperature.
The time required for each replacement is estimated to be about one hour.

[Yamaguchi, Oshima, Komori]

We excited pitch resonances around 44Hz in MN, and measured the resonant frequency and Q-value of the pitch in the CuBe wire between IM and MN.
We used the ports for exciting: 
K1:VIS-ETMX_MN_TEST_P_EXC
K1:VIS-ITMX_MN_TEST_P_EXC
K1:VIS-ETMY_MN_TEST_P_EXC

The starting times for ringdown and signals, which can be used for Q measurement, for each suspension are as follows:
ETMX:
01:30:05 UTC: K1:VIS-ETMX_NBDAMP_P3_OUT_DQ
ITMX:
07:04:00 UTC: K1:VIS-ITMX_NBDAMP_P3_OUT_DQ
ETMY:
07:39:15 UTC: K1:VIS-ETMY_NBDAMP_P3_OUT_DQ

We estimated the Q factors of the pitch mode of the CuBe wires, corresponding to the Q factors derived from the ringdown measurement. The results are presented in the attached figure and summarized in the following list.

The estimation errors for the resonant frequency and the Q-value are 10 mHz and 0.1e3, respectively. 

The Q-values are measured from the line widths of the spectra in klog25931; ETMX was measured at 80 K, and ITMX and ETMY were measured at 250 K. In comparison, all measurements today were made at 80K.
Q-value of ETMX changed compared to previous measurements under the same conditions as this one.The fact that the Q-value measurement results have changed from the past means that the spectrum has become thicker, so the resonance frequency may have changed during the measurement.
ITMX had a higher Q value at 80K than at 250K, while ETMY had a lower Q value at 80K than at 250K.